# Why dont we all want rocket mass heaters?



## electrathon (Jan 19, 2017)

I have wondered this for some time.  I just saw a rocket stove (different than a rocket mass heater, but similar) pic posted in another thread and figured I would ask the question.

Do rocket mass heaters actually work or are they a temper mental nightmare?  If they do work why are they not common?  I do not see them talked about often here, is there a reason?  People afraid of the inside the house fire going to burn your house down?  Too long to get them to temperature?  Not enough firewood consumed?  Just looking for input.


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## bholler (Jan 19, 2017)

electrathon said:


> Do rocket mass heaters actually work or are they a temper mental nightmare?


By rocket mass heaters are you talking about the european style masonry heaters?


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## electrathon (Jan 19, 2017)

bholler said:


> By rocket mass heaters are you talking about the european style masonry heaters?


Sort of.  They look to me to get lit off and work as a blast furnace, allowing the draft to run the fire very, very hot.  Think of a constant rush of a chimney fire.  They burn small wood, and just feed off the end of the pieces as they burn.  https://richsoil.com/rocket-stove-mass-heater.jsp  There is usually mass around them, gravel, clay, etc that heats, then you let the stove go out after an hour or two and the thermal mass radiates.


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## bholler (Jan 19, 2017)

nevermind i just looked up the term and yeah I know what they are.  The problem is that it is a huge site built structure that really is not approved at all.  They can be safe but no inspector or insurance company is going to know what to make of them.  Also they typically have small fireboxes that need lots of loading.  Yes you only burn them a few hours a day if it is sized right for your house but are you going to want to stand there and feed wood in for a couple hours?  Not me.   Masonry heaters are much more effective and practical but either way you need a foundation for it and it will take up allot of space.


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## husky345 vermont resolute (Jan 19, 2017)

Who wants to looks at a rusty old barrel in they're house 


Sent from my iPhone using Tapatalk


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## bholler (Jan 19, 2017)

husky345 vermont resolute said:


> Who wants to looks at a rusty old barrel in they're house


They dont have to have the barrel visible or even use a barrel.  There is a very nice looking one in a cool earth sheltered home that we work in.  But they dont use it they had us install a traditional wood stove instead they said it is much easier to use.


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## jatoxico (Jan 19, 2017)

We do, but you know who won't like it.


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## bholler (Jan 19, 2017)

jatoxico said:


> We do, but you know who won't like it.


Why would you want one of them over a traditional wood stove or a masonry heater?  They do work but they take all but constant feeding while you are burning.  If they were more user friendly there would be groups designing them and getting the designs approved like the masonry heater association.  There just is not enough demand.


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## jatoxico (Jan 19, 2017)

bholler said:


> Why would you want one of them over a traditional wood stove or a masonry heater?



Wasn't really a serious comment holler. They are cool but not very practical as you outlined.


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## electrathon (Jan 19, 2017)

OK, the constant feed part makes since.  I was wondering how fast the consumption was when they were rocking.  I do see that they are allowed in Portland Oregon, a good example here of what is safe, allowable or legal in one place but not elsewhere.  If you read through some design plans, the concept can be pretty small, likely only a few hundred pounds.  That small though and it nullifies the idea of only a fire every day or two.


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## bholler (Jan 19, 2017)

jatoxico said:


> Wasn't really a serious comment holler. They are cool but not very practical as you outlined.


fair enough sorry


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## electrathon (Jan 19, 2017)

bholler said:


> Why would you want one of them over a traditional wood stove or a masonry heater?  They do work but they take all but constant feeding while you are burning.  If they were more user friendly there would be groups designing them and getting the designs approved like the masonry heater association.  There just is not enough demand.


There are groups designing them and they are being approved, that was why I was questioning why they are not more talked about here.  The stated advantage over conventional wood stoves is a fraction of the wood use.  They have minimal heat lost to exhaust, kind of like a pellet stove exhaust..


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## bholler (Jan 19, 2017)

electrathon said:


> I do see that they are allowed in Portland Oregon, a good example here of what is safe, allowable or legal in one place but not elsewhere. If you read through some design plans, the concept can be pretty small, likely only a few hundred pounds. That small though and it nullifies the idea of only a fire every day or two.


The problem is what standard are they built to to ensure they are safe?  They are site designed and built they are only as safe as the person building it makes them.  The same goes for an open fireplace but the dig difference is that there is a standard to build to to ensure you have proper thicknesses and clearances.  There is absolutely no inherent safety issue with the concept but there is allot of room for major safety issues.


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## bholler (Jan 19, 2017)

electrathon said:


> The stated advantage over conventional wood stoves is a fraction of the wood use. They have minimal heat lost to exhaust, kind of like a pellet stove exhaust..


Yeah according to the guys promoting them.  What they claim and what you get in the real work are very different.  And no matter how hot you burn that fire unless you keep the exhaust above the condensation point till it exits the house you will have creosote buildup.  There is no way around it when burning wood.


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## electrathon (Jan 19, 2017)

husky345 vermont resolute said:


> Who wants to looks at a rusty old barrel in they're house
> 
> 
> Sent from my iPhone using Tapatalk


they do not have to be a rusty barrel.  They can be stainless, can be rolled steel, etc.    This is sort of like saying we do not want a wood stove in the house because they are made out of rusty barrels.  They can be, but they can be made from other things too.


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## branchburner (Jan 19, 2017)

electrathon said:


> I do not see them talked about often here, is there a reason?  People afraid of the inside the house fire going to burn your house down?



Like bholler says... code and insurance. I'm sure more DIYers would consider them if it weren't for that.


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## sportbikerider78 (Jan 19, 2017)

I have no idea what we are talking about...but I love the idea of saying I have a rocket stove.


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## electrathon (Jan 19, 2017)

bholler said:


> Yeah according to the guys promoting them.  What they claim and what you get in the real work are very different.  And no matter how hot you burn that fire unless you keep the exhaust above the condensation point till it exits the house you will have creosote buildup.  There is no way around it when burning wood.


That was what I was wondering.  What the real world issues were compared to the people talking of them.  I do know that it is possible to burn a wood fire so that there is less/little creosote build up.  I have not cleaned my shop stove ever in 25 years and there is zero build up (I check every so often).  Also some stoves burn clean, some dirty, I suppose it is possible that they are burning clean.


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## bholler (Jan 19, 2017)

electrathon said:


> . I do know that it is possible to burn a wood fire so that there is less/little creosote build up. I have not cleaned my shop stove ever in 25 years and there is zero build up (I check every so often). Also some stoves burn clean, some dirty, I suppose it is possible that they are burning clean.


Yes your stack is clean because you are putting enough heat up the stack to carry it all out.  When burning wood the exhaust temps need to stay above the condensation point so basically above 220 till it exits the chimney.


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## electrathon (Jan 19, 2017)

sportbikerider78 said:


> I have no idea what we are talking about...but I love the idea of saying I have a rocket stove.


I have to agree.  If you renamed it a candle flame heater it would be far less appealing.  Kind of like calling an older woodstove a smoke dragon, like a racial slur for stoves.  We don't necessarily know that they are bad stoves, just that they have not joined into the EPA club many of us now live in.  Rocket mass heater sounds like an awesome wood burner.


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## peakbagger (Jan 19, 2017)

Take a look at a Jetstream or Dicks Hills design, Its basically rocket mass heater with much large capability to heat a large thermal mass as it has an external storage tank. Incredibly clean burn and super efficient. .


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## ddddddden (Jan 19, 2017)

Here's your rocket stove forum.
https://permies.com/mobile/f/125/rocket-stoves

I guess we're not cööl enough to have a röcket forum.

But yeah, as you noted, hundreds of lbs isn't going to get it done. You need thousands of lbs of thermal mass to capture enough heat to keep a house comfortable for a day after the fire is out. Unless they're building a sod house, I agree that most folks looking for this kind of heat would go with a traditional masonry heater, which burns the inferno in a proper firebox and captures the heat in a convoluted exhaust path.

https://en.m.wikipedia.org/wiki/Masonry_heater


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## iamlucky13 (Jan 19, 2017)

I hadn't seen this variation on a rocket stove before, but looking at it, it does make sense as a scaled up and improved rocket design.

I'm not really convinced they outperform the better firebox stoves and avoid the potential for creosote issues, and the installation planning seems like it would be far more complicated.

I also see a lot of utterly absurd claims being made about them. The first site I found claimed 10x the efficiency of a 75% rate woodstove. Even they knew that was an absurd claim, though, and qualified it in their FAQ's, concluding that aside from laboratory conditions, "An excellent operator might be able to get about 35% efficiency. Most people run their '75% efficient wood stove' at 3% to 15% efficiency."

That's interesting then, because by my calcs, at 30 degrees outside temperature, I should need to be burning somewhere between 200 pounds if I'm an "excellent operator" and 2250 pounds of wood per day to keep the house at 70 degrees. I've never tried to weigh my use, but I seriously doubt I've ever exceeded 100 pounds, which based on my estimated heat loss would be in the ballpark of 70% efficiency.

I'd love to know who they found who was burning over 1/2 a cord per day!


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## byQ (Jan 19, 2017)

Hi electrathon, I'm in Idaho but have spent most of my life in Oregon. I just built a big masonry heater, https://www.hearth.com/talk/threads/mh-puzzling-together.155464/#post-2089184.

I think the attraction to rocket/rocket mass heaters is that someone can build one themselves, and do it cheaply. Masonry heaters scare do-it-yourselfers due to their perceived complexity and cost. I know there are some masonry heater builders who are delving into rocket mass heaters because many people are interested in them. It all starts with a coffee can and takes off from there.

In your area a class is taught in Eugene by Max Edleson http://www.firespeaking.com/

Another masonry heater builder teaches a class on RMH's in Minnesota, Eric Moshier http://solidrockmasonry.com/. He says masonry heaters are far superior - they burn hotter, less fuss, and are more durable. But there is an interest in rocket heaters so he teaches a class.

I don't think open fireplaces are allowed in new construction in Oregon. But you say RMH's are? My sister lives in Portland and wants a masonry heater. I gave her all the hardware for one and plans. We'll see......


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## electrathon (Jan 20, 2017)

byQ said:


> .
> https://www.hearth.com/talk/threads/mh-puzzling-together.155464/#post-2089184
> ...
> 
> ...


I saw on the site that they said that some areas are allowing them.  Portland was used as an example place.  It is possible it is not true.  I am not sure about fireplaces, I will have to ask our inspector about that.


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## electrathon (Jan 20, 2017)

byQ said:


> .
> https://www.hearth.com/talk/threads/mh-puzzling-together.155464/#post-2089184
> 
> I don't think open fireplaces are allowed in new construction in Oregon. But you say RMH's are? My sister lives in Portland and wants a masonry heater. I gave her all the hardware for one and plans. We'll see......


I saw on the site that they said that some areas are allowing them.  Portland was used as an example place.  It is possible it is not true.  I am not sure about fireplaces, I will have to ask our inspector about that.


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## tpenny67 (Jan 20, 2017)

I've got to wonder how any heater that relies on thermal mass would work in New England where 40 degree temperature changes in one day are common.  Unless the house is uber-insulated, it seems that by the time the time the thermal mass is warm enough for a sub-zero night it will be baking the house the next day when a warm front comes in.

Also, from the little I've read online, one potential problem with a rocket heater is back drafting on a windy day at the beginning and end of the fire.


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## electrathon (Jan 20, 2017)

tpenny67 said:


> I've got to wonder how any heater that relies on thermal mass would work in New England where 40 degree temperature changes in one day are common.  Unless the house is uber-insulated, it seems that by the time the time the thermal mass is warm enough for a sub-zero night it will be baking the house the next day when a warm front comes in.
> 
> Also, from the little I've read online, one potential problem with a rocket heater is back drafting on a windy day at the beginning and end of the fire.


I could see the thermal mass issue being a problem with overheat or too long to heat up.  I would guess it is similar to having a floor heat system that has cement as a floor.   As to back drafting, it seems that it would not be that different from a conventional stove.  I was curious on how hard it was to get the draft started they seem to have a complicated chimney path.


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## tpenny67 (Jan 20, 2017)

electrathon said:


> I could see the thermal mass issue being a problem with overheat or too long to heat up.  I would guess it is similar to having a floor heat system that has cement as a floor.   As to back drafting, it seems that it would not be that different from a conventional stove.  I was curious on how hard it was to get the draft started they seem to have a complicated chimney path.



My understanding (could be wrong) is that rocket stoves have a much cooler exhaust and sometimes don't even have a conventional chimney at the end.  They rely on a raging fire in the vertical section to keep the air moving, and when that raging fire dies down...

Also, since standards are lacking and most rocket stoves are individually designed and built, there's plenty of room to make a bad design.


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## electrathon (Jan 20, 2017)

tpenny67 said:


> My understanding (could be wrong) is that rocket stoves have a much cooler exhaust and sometimes don't even have a conventional chimney at the end.  They rely on a raging fire in the vertical section to keep the air moving, and when that raging fire dies down...
> 
> Also, since standards are lacking and most rocket stoves are individually designed and built, there's plenty of room to make a bad design.


I have read that the exhaust is very cool, much like or even exceeding a modern wood stove.  The wood, wood gas, creosote is almost all burned.  As long as there is a vertical stack the draft should continue.  This does rely on a lot of other factors though, mainly positive verses negative pleasure in the house.  If there is not an outside air source I could see someone turning on a bathroom fan or similar and reversing the draft.  We already have that issue with our stoves though, as you said, worse during start up or shut down cycles.


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## Poindexter (Jan 20, 2017)

I looked into this a few years ago.  

My blazing success was a 'pocket rocket'.  5 gallon metal bucket with 48" of four inch exhaust stack, maybe 18" of 6" swsp as the fuel magazine and a 9" cone of orange glow at the top of the stack.  If id had a safe platform to stand on a couple feet above grade i could grill some killer crusts onto some ribeyes with that.

I built several J stoves, all outdoors in the snow.

Throat diameter is the key dimension.  J stoves with a 4" throat will not run dependably on cord wood no matter how small it is split, at least with my local trees.  Twist and bow in the splits causes the a:f ratio in the burn chamber to vary.

I did get a couple 6" throat J stoves running pretty good in cord wood, but even then something like 80% of my cordwood is too twisty to bother splitting smaller.

If the wife and i sell our big house on the small lot and move to a small house on a big lot i will probably put a sofa shaped rmh on an outdoor patio.

A lot of the threads on permies, when i was active there were "i bought the book, didnt follow the directions and now my stove doesnt work right."

If you are really curious, the pdf for a pocket rocket was free.  Build one of those first.  Crazy amount of heat out of a few little sticks, right now.

Second, google up ' dr peter rocket stove', should get some links to a phd in holland...

Third, buy the book from permies, 16 bucks i think for the pdf, but rtfm and follow the proportions.


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## electrathon (Jan 20, 2017)

Poindexter, thank you for the input.  I will read up more.  " Crazy amount of heat out of a few little sticks, right now".  This is what got me really curious.  If altering the way we are burning gets more heat it seems it would be a very good thing.  How much did you have to tend to the stove?  Constantly, off and on or about what happens with a wood stove?  It seems that if the main concern with them is having a fire going inside your house you could have the initial firebox opening outside, then have the thermal mass inside the house.  Possibly having to go outside to tend to it would be uncomfortable.


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## Poindexter (Jan 20, 2017)

electrathon said:


> Poindexter, thank you for the input.  I will read up more.  " Crazy amount of heat out of a few little sticks, right now".  This is what got me really curious.  If altering the way we are burning gets more heat it seems it would be a very good thing.  How much did you have to tend to the stove?  Constantly, off and on or about what happens with a wood stove?  It seems that if the main concern with them is having a fire going inside your house you could have the initial firebox opening outside, then have the thermal mass inside the house.  Possibly having to go outside to tend to it would be uncomfortable.



I don't know that it gets more heat, just the rapid primary and secondary burn can get all the BTUs out in a hurry.  Just like a raging fire in a masonry heater.

The RMH basically uses adobe instead of stone as the mass storage device.

I have thought for years it would be handy for "someone" to get a firebox and secondary burn chamber of a typically sized masonry heater through the EPA testing process so home builders could just install a EPA approved masonry heater and then box out the smoke path however works on the floor plan.  Heaven forbid the EPA spend my tax dollars on that.  

Once the critical dimensions are known, the developer who sunk a million bucks into testing will never sell another one and will never break even on the "approved" design.


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## bholler (Jan 20, 2017)

Poindexter said:


> I have thought for years it would be handy for "someone" to get a firebox and secondary burn chamber of a typically sized masonry heater through the EPA testing process so home builders could just install a EPA approved masonry heater and then box out the smoke path however works on the floor plan. Heaven forbid the EPA spend my tax dollars on that.


Uhhh the epa would not be spending any money on it at all it would be the manufacturer who spent the money on development and testing.  And the smoke path would have to be predetermined as well that has a lot to do with how the stove would operate.


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## begreen (Jan 20, 2017)

The Alliance for Green Heat instrumented a kachelofen and a dragon rocket heater for 3 days of testing at the first stove decathalon in D.C. The masonry heater performed very well and Matt's modified rocket stove impressed the judges. 
http://www.forgreenheat.org/stovedesign/finalists.html
http://forgreenheat.blogspot.com/2013/12/a-brief-analysis-of-stoves-at-wood.html
@John Ackerly can provide more details on the testing. John, do you know what Matt is up to lately?


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## Poindexter (Jan 20, 2017)

bholler said:


> Uhhh the epa would not be spending any money on it at all it would be the manufacturer who spent the money on development and testing.  And the smoke path would have to be predetermined as well that has a lot to do with how the stove would operate.



While I agree the former is the standard operating procedure, I find it unfortunate.  I have no idea what the EPAs budget was last year, but I bet it was enough for a couple guys to log off facebook long enough to build and test a couple prototypes through certification.  

For the latter, any vehicle owner in the US, last I knew even in California, can install any exhaust they want from the outlet of the catalytic converter on back.  Subject to state and local noise regulations of course, but as long as the emissions equipment is unaffected custom "cat backs" are federal legal.  A well designed masonry heater should be the same.  Once the primary and secondary burns are complete in the first two chambers, the exhaust gas should be legal and the rest of the piping between the secondary chamber outlet and chimney cap is of no concern to the emissions regulators.

What I would like my tax dollars to be spent on, and what my tax dollars are actually spent on are two entirely different realities.


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## electrathon (Jan 20, 2017)

Poindexter said:


> .
> 
> What I would like my tax dollars to be spent on, and what my tax dollars are actually spent on are two entirely different realities.


You do have to be careful about this sort of thinking.  As of today, you my be happy about the results.  As of yesterday you may not have.  They could have taken your dollars and used the money to attack wood burners like they used your dollars to try to put the coal industry under and force an entire part of the country onto public assistance.  Sometimes it is better if the people do things without the "help" of government.


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## jetsam (Jan 20, 2017)

Rocket stoves are a big deal for cold people who have access to stone or clay and wood. It's at least an order of magnitude more efficient than an open fire.

I won't be swapping out my BK for one, but it is good to know the principle. I'll be surprised if I don't find an ad hoc use for a cinder block rocket at some point.


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## bholler (Jan 20, 2017)

Poindexter said:


> A well designed masonry heater should be the same. Once the primary and secondary burns are complete in the first two chambers, the exhaust gas should be legal and the rest of the piping between the secondary chamber outlet and chimney cap is of no concern to the emissions regulators.


The difference is that the venting system of a wood burner determines the draft and on a masonry heater if the internal heat exchange passages are not designed correctly regardless of how good the combustion box design is it will not work.  If you think that nothing past the combustion chamber has an effect on the emissions you have allot to learn about wood stoves.




electrathon said:


> like they used your dollars to try to put the coal industry under


The economics of coal mining and the availability of cheap natural gas is what put the coal industry under.  It was on its way out long ago.  Believe me I live in coal country the coal industry died on its own.


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## bholler (Jan 20, 2017)

Poindexter said:


> I bet it was enough for a couple guys to log off facebook long enough to build and test a couple prototypes through certification.


Do you really think that the epa has stove designers on staff?


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## Poindexter (Jan 21, 2017)

Had a bit of a bad dream over night.  The hotrodders putting cat back on modern vehicles, in general, are looking to maximize airflow for best acceleration.

@bholler is correct that hanging enough pipe or masonry, on an otherwise clean burning fire box,  can turn it into a heavy smoker.


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## Poindexter (Jan 21, 2017)

jetsam said:


> Rocket stoves are a big deal for cold people who have access to stone or clay and wood. It's at least an order of magnitude more efficient than an open fire. I won't be swapping out my BK for one, but it is good to know the principle.



Pretty simple, but I agree burn a small of wood or dry grass hot and fast in the rocket stove portion of the assembly and then store the heat in a mass of adobe or stone.  I won't be swapping out my BK either. 

It would be handy for me to have a masonry stove of some kind with one surface taking up a  section of the garage wall.  When my wife gets home from work with her cold car I could fire thing hot and fast and use at least some of that heat to warm the garage and her car back up without having to burn oil to do it. 



jetsam said:


> I'll be surprised if I don't find an ad hoc use for a cinder block rocket at some point.



The cinder block rocket doesn't work for beans.  What you see in the youtube is about all it can do, no secondary burn.  I experimented quite a bit last summer.

My church is one of many that sends teams annually to knows how many orphanages there are in Haiti.  Our particular group of kids is running out of wood to cook what food they have.  While everybody else in the congregation was praying for a solution, I decided to build a cinderblock rocket to see if I could get it running on dry grass. 

Got some dry hay from a neighbor with a couple horses, and split some of my straighter cord wood pretty small.  I built the first one as shown on youtube, and WYSIWYG, no secondary.  The throat on that thing is in the wrong place for starters, and the vertical isn't tall enough for another.

I dug my bentonite clay out of the tool shed (handy stuff, bentonite) and got to sculpting and sealing.  At the extreme I filled the elbow with enough bentonite to put the throat where it belongs and fabbed up a P-channel out of sheet metal to introduce preheated turbulent air just down stream from the throat where secondary burn should be igniting.  If you get one working good with a dependable secondary burn going on please do send me a PM or start a new thread.

The pocket rocket will work, very well, the first time.  Here is the exhaust cone on mine.





I am not finding the exact .pdf I built from this morning, but any of these should work well.

https://canadiandirtbags.wordpress.com/2010/12/05/how-to-build-a-pocket-rocket/

http://homesteadlaboratory.blogspot.com/2014/01/pocket-rocket-stove.html

http://www.rocketstoves.com/pdf/pocketrocket.pdf

If the neighbors aren't pulling back the curtains to see the jet airplane crashing into your back yard, well, you don't have enough draft and it isn't really a rocket stove yet.


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## HisTreeNut (Jan 21, 2017)

I made a tin can rocket stove after watching a plethora of on-line videos.  The stove does generate a serious amount of heat.  Looking at a few other videos in my research, a rocket stove is imho a mini-forge.  You could melt metal with this thing if you wanted to.  

You can also use the stove to boil water.  Watching videos, the stoves will need a gas stove burner grate [or something to that effect to allow gases & heat to escape]. If you don't, your fire will not burn correctly and/or die out.  That being said, a properly built & vented stove will boil a couple of cups of water in 2 - 4 minutes.  A gallon of water boils in 8-12 minutes in the same situation.  Covering the pot allows for faster boil times.  
Once I got mine working, and the novelty wore off, I used it as a marshmallow roaster.  About 10 minutes to get hot, and it roasts marshmallows in about 5-10 seconds.

I made a video of the rocket stove in my fireplace before we installed the Buck.  At this moment, i cannot figure out how to upload or post it.  Anyone know how to post an old iPod video?

Mistakes I have seen in people's videos:

1) In most of the videos of the tin can stoves do not have enough height in the chimneys.  You should see virtually no smoke coming from the top of the stove and without out height, the gases do not re-burn well, much less re-burn at all.  Most videos show a raging fire and smoke billowing everywhere.  That is not what you want at all.

2) In a lot of the videos, you see flame coming out of the top of the cans.  If you see flame coming from the top of the cans, there is too much wood in the stove or the wood has not burned down enough to cook and so on.

3) Even though I "insulated the can with ash," the can still gets ridiculously hot...I used duct tape for the test because I couldn't find my aluminum tape anywhere [in a a box.  It started melting after about 30 minutes & I sprayed the tape with a water bottle to slow the inevitable melting process...the water that hit the metal evaporated almost instantly.  If you were to build one of these things, I would not set up the stove on top of a table directly, but I would place it on some bricks or stone of some kind.

FWIW, it is a neat "technology" and something fun to play with.


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## mjstef (Oct 24, 2017)

I ran one in my greenhouse in Montana.  Gotta find the pics.   Most all heat is absorbed in the mass and nothing but vapor out the flue.   I could get to the entire loop in my greenhouse through 3 cleanouts.   Being it's so efficient it burns very little wood and never got more than a cup or so of creosote ect out of 40' of pipe.

Anyways when i get my hunting cabin built i will likely do one their. Wife likes something like this.....   https://i.pinimg.com/736x/7a/c2/07/...610b6b9b--rocket-mass-heater-thermal-mass.jpg

http://www.terre-et-flammes.fr/portfolio/seine_et_marne/


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## putttn (Oct 24, 2017)

mjstef said:


> I ran one in my greenhouse in Montana.  Gotta find the pics.   Most all heat is absorbed in the mass and nothing but vapor out the flue.   I could get to the entire loop in my greenhouse through 3 cleanouts.   Being it's so efficient it burns very little wood and never got more than a cup or so of creosote ect out of 40' of pipe.
> 
> Anyways when i get my hunting cabin built i will likely do one their. Wife likes something like this.....   https://i.pinimg.com/736x/7a/c2/07/...610b6b9b--rocket-mass-heater-thermal-mass.jpg



That is a Rocket Mass Heater. Probably very similar but he does not use any stone or mass to retain the heat.


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## georgepds (Oct 25, 2017)

electrathon said:


> OK, the constant feed part makes since.  I was wondering how fast the consumption was when they were rocking.  I do see that they are allowed in Portland Oregon, a good example here of what is safe, allowable or legal in one place but not elsewhere.  If you read through some design plans, the concept can be pretty small, likely only a few hundred pounds.  That small though and it nullifies the idea of only a fire every day or two.




Is it because it's always raining in portland?


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## begreen (Oct 25, 2017)

Moved the Liberator to its own thread so that this one can stay on the topic of rocket *mass* heaters. 

https://www.hearth.com/talk/threads/liberator-rocket-heater.163878/


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## paul wheaton (Nov 6, 2017)

I just found this thread.   There are some links to my stuff earlier in this thread.   I am not one of the top five brains in rocket mass heaters, but I think I might make the top ten list.  

Here is my feeble attempt to answer some questions ...

> Do rocket mass heaters actually work or are they a temper mental nightmare?

They do work.   I have one in my three bedroom house in montana.  I heated my house last winter with 0.60 cords of wood (I measured VERY carefully last winter).   I would usually go to bed with the house at 70 degrees and wake up to the house at 68 degrees.  I would usually start a fire when it got to 66 degrees and stop feeding the fire when it got to 72 degrees.   This was usually a 90 minute burn every other day.  There were some sub-zero days where I would do a three hour burn every day.   

> If they do work why are they not common?

I think there are hundreds of thousands of them in existence now.   But that is just a guess.

I am surprised that people still buy any sort of wood stove when they could have a rocket mass heater.

> The problem is that it is a huge site built structure that really is not approved at all. 

It is mostly a DIY sort of thing.  

Approved in portland and ... last I heard ... about a dozen other cities.   I've been told that a lot of insurance companies are coming around too.

The thing is that nine years ago they were pretty rough.  But they have come a LONG way in the last few years.  As of last year there is now an excellent book and ...  I put out some DVDs, so my judgement of the DVDs would be very biased.

> they typically have small fireboxes that need lots of loading. 

The batch box rocket mass heaters have really big fireboxes.  The J-tube style has a super tiny firebox.   The one in my house is a j-tube style - and it is smaller than average too.   But as I said earlier, most of the winter I burn a 90 minute fire every other day.   So I start the fire, go work in my office, go back every 20 minutes to add wood until I forget and the fire goes out.   

I lived in a similar sized house with a conventional wood stove, and I remember feeding it a mountain of wood throughout the day on days where it wasn't all that cold outside.   The loading of a rocket mass heater is a dream in comparison.

> are you going to want to stand there and feed wood in for a couple hours? Not me.

I don't know of anybody with a rocket mass heater that does that.

> Masonry heaters are much more effective and practical but either way you need a foundation for it and it will take up allot of space.

Rocket mass heaters have a lot in common with masonry heaters.   Rocket mass heaters tend to heat a space with less wood, are built in a weekend (instead of three months) and cost a few hundred dollars (instead of $10,000 and up).


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## paul wheaton (Nov 6, 2017)

> Who wants to looks at a rusty old barrel in they're house

I have a stainless steel barrel for mine.   And I have seen people use a fabricated barrel shape.   And we have a tiny cabin here with a rocket mass heater that is all masonry, no barrel or barrel-like thing.  

> The stated advantage over conventional wood stoves is a fraction of the wood use.

Typically one tenth the wood.   In other words, people that have replaced a conventional wood stove with a rocket mass heater have reported that they are more comfortable and are heating with one tenth the wood.

Some people choose to build a rocket mass heater that is designed more for "ease of use" than for efficiency, and they tend to get closer to one fifth or one eighth the wood.  

> They have minimal heat lost to exhaust

Usually about 70 to 140 degrees F.   Most conventional wood stoves are required by law to exhaust at 350 or higher.  That's a lot of heat going outside.

> There is absolutely no inherent safety issue with the concept

Which will always be the case with anything new.  

At the same time, the new book is quite excellent at covering safety.   This makes for a wood heater that is far safer than a conventional wood stove.   And one of the big reasons for that is that we burn so much less wood.   While the house next door is burning all day, we burn for just an hour or two.  


> What they claim and what you get in the real work are very different.

Really?   I think we are really good about sharing our numbers.   And I very, very carefully measured exactly how much wood I used last winter and what the indoor and outdoor temperatures were.  

> And no matter how hot you burn that fire unless you keep the exhaust above the 
> condensation point till it exits the house you will have creosote buildup. There is 
> no way around it when burning wood.

Unless, of course, we have a way around it.   

Most wood stoves burn at about 1000 degrees F.   We shoot for temperatures over 1800 degrees F.   Thus burning the creosote.

We insulate the burning area to force a much higher burn temperature, and THEN we harvest the heat.

Rocket mass heaters don't have creosote.


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## paul wheaton (Nov 6, 2017)

> one potential problem with a rocket heater is back drafting on a windy day at the beginning and end of the fire.

I have not ever seen that problem.   The barrel acts as a sort of upside-down hot-gasses p-trap.  

> I could see the thermal mass issue being a problem with overheat or too long to heat up.

I have not experienced overheat, but there are cases where if you have been away for several days, it can take a while to get the mass hot.   We can have an issue that we call "a cold plug" under the right conditions.

> If there is not an outside air source I could see someone turning on a bathroom fan or similar and reversing the draft.

Once my rocket mass heater is running, I have turned on the kitchen fan, both bathroom fans and the clothes dryer and it still runs hard in the correct direction.

Of course, if the mass is cold and I want to start the fire, and all four of those things are running - I can feel the air blowing the wrong way.   Just as I have experienced the exact same problem with conventional wood stoves.

>  My blazing success was a 'pocket rocket'. 

Pocket rockets are pretty interesting.  I now choose to never use them.  The design of the pocket rocket typically results on the insides melting/burning/spalling out.

> J stoves with a 4" throat will not run dependably on cord wood no matter how small it is split

For a long time a lot of the pros said that 4 inch was a novelty for outdoors only.   But now a lot of the issues have been resolved and people are creating some rather excellent 4 inch systems.


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## paul wheaton (Nov 6, 2017)

> you could have the initial firebox opening outside, then have the thermal
> mass inside the house. Possibly having to go outside to tend to it would
> be uncomfortable.

Bingo.   Many people have tried this path and found it to be rather annoying.

> I made a tin can rocket stove ...

The rocket mass heater is built on rocket stove philosophies.  But we are struggling with people that are worried that everybody in the house will die if you put in a rocket mass heater.  It turns out they thought we were talking about running an outdoor cook stove inside of a house.   So we are working to stop saying "rocket stove".  A "rocket stove" is designed for outdoor use.   A "rocket mass heater" is designed for indoor use and the exhaust is routed outside.  

I'm not saying that you suggested the two are in any way similar.   I just want to point out this important difference in vocabulary.


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## bholler (Nov 6, 2017)

paul wheaton said:


> I just found this thread.   There are some links to my stuff earlier in this thread.   I am not one of the top five brains in rocket mass heaters, but I think I might make the top ten list.
> 
> Here is my feeble attempt to answer some questions ...
> 
> ...



Ok how many btu s are you inputting with that .6 cord.  You must have a very low btu load to be able to heat with that little wood.

What is the difference between a batch box rocket and a masonry heater?

If they are only approved in a dozen or so cities they have a long way to go before they are a viable solution for most people.

What type of stove were you using?  There are stoves out that can burn 48 hours on a single load.  And the majority go 8 hours on a load.

You say no one loads wood for a couple hours.  But you also said you sometimes burn for 3 hours.  And you load every 20 mins.  To me between loading and getting the wood to load that sounds like a lot of work that I have no interest in doing.

If you are building a simple masonry heater diy there is no reason for it to take 3 months or $10000.  In fact 3 of us built one in a friends shop in a weekend for about $1200.  Granted we were all chimney masons though.

I see nothing wrong with rocket mass heaters and I hope they get developed more and get more approval.  But honestly the claims of efficiency gains sound pretty far fetched.  There is only a certain ammout of btu s available in wood and no matter how you burn it you cant change that.


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## paul wheaton (Nov 6, 2017)

I am burning pine, fir and larch.  


> What is the difference between a batch box rocket and a masonry heater?

A batch box rocket mass heater has a very specific shape to the wood feed - and is generally fed through a door, a lot like a conventional wood stove.  It is now the most popular design for rocket mass heaters, although I think it still has a few kinks to work out.  

A batch box rocket mass heater will have a vertical port in the back that is an exact shape and size, and a low air intake on the door that cannot be plugged.  It has an insulated vertical riser that is typically about four feet tall.

It tends to burn cleaner and hotter than a masonry stove, and the exhaust temp tends to be lower.


> If they are only approved in a dozen or so cities they have a long way to go before they are a viable solution for most people.

Nearly everybody can build them outdoors (greenhouses are quite popular).   And it seems that the way to get them approved in cities is to have people build them, without permission, in cities where they are not allowed, and then do a huge amount of documenting before doing the work to get them added to the city codes.  A path only for the most durable people.   Since the exhaust is nearly invisible, I have heard of people building and operating them without permits - just for the sake of heating so cheaply.    And, of course, there are places where there are no building codes and there are places where people have a cabin where codes appear to not apply.

There are a lot of people actively working on getting them into the codes of more places.   The lawmakers appear to be quite keen on rocket mass heaters, so I have heard it has not been too difficult.   But I confess that this is not an area I have put much of my time into.


> What type of stove were you using?

Hmmmm, here is one I was using about nine years ago when I first learned about rocket mass heaters.  








I took the picture because I caught two mice with a bucket.  

I remember feeding a LOT of wood into the stove and it just never seemed like enough.


> You say no one loads wood for a couple hours. 

I don't understand what you are saying.   

For a lot of the winter, I will go a couple of days between fires.

> But you also said you sometimes  burn for 3 hours. And you load every 
> 20 mins. To me between loading and getting the wood to load that sounds 
> like a lot of work that I have no interest in doing.

On a regular winter day with temps below freezing at night and above freezing during the day, I will run a fire every other day for about an hour and a half.  

On a really cold winter day, with temps holding below zero  all day, I will run a three hour fire every day.

Since the wood feed on my j-tube style rocket mass heater is pretty small, then I reload it every 20 minutes or so.   My wood feed is about 7 inches by 5 inches and 17 inches deep (to take standard firewood).  So it isn't much of a load.  

There are people with a similar sized batch box wood feed would guess about how much heat they want for the day and load it once every other day.


> Granted we were all chimney masons though.

There's the catch.  

Even still, that has to be some sort of record.  Three experts to build it in one weekend.   I would have thought three experts working 12 hours a day and 100% of the materials on hand ...  pushing to build as fast as they can .....   in a shop instead of a house ....   I would have put my money on five days.  

In a house with one pro and a non-pro assistant ...   I think you will agree with three months and a $10,000 minimum.

> But honestly the claims of efficiency gains sound pretty far fetched. 

You are not the first to doubt.   Here is me and several experts talking about this very topic:




> There is only a certain ammout of btu s available in wood and no matter how 
> you burn it you cant change that.

There is also the question of how well you keep the heat in the house instead of putting it out the chimney.

I think that if I get insulated curtains, but a mudroom/enclosed-porch on the front of my house and make three changes to my rocket mass heater, I can go from 0.60 cords of wood for winter down to 0.4.


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## bholler (Nov 6, 2017)

Ok so how many btu s are in your .6 cord of wood?

How can you compare efficiencies if you don't know what wood stove you had or how much wood you used?

And as far as a masonry heater goes no it should never take 3 months of work at all.  And most of the cost is in the finishing materials.  Now for our build it was in a shop with a thick enough floor so no foundation needed.  And he had precast a couple refractory panels for certain parts 2 in a day 2 weeks earlier.  But the rest was all built by 3 of us in 2 10 hour days and honestly not working any harder than a normal day.  Yes it was a relatively small simple unit but you claim of 3 months is completely off base.


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## paul wheaton (Nov 6, 2017)

> How can you compare efficiencies if you don't know what wood stove you had or how much wood you used?

You will note that I did not compare the efficiency of the stove in the picture with what I have now.  Other than to say that I have a LOT of experience in feeding a LOT of wood (many cords) to conventional wood stoves.   You asked what stove was I using - I assumed you wanted to hear about what sort of conventional wood stove I used previously.  So I shared one I happened to have a picture of. If you recognize the brand and whatnot - more power to you.  

I have not personally racked up several years with a wood stove in one house and then replaced it with a rocket mass heater and then racked up several years with a rocket mass heater.    I have, however, racked up many years in many homes with conventional wood stoves, and then when I arrived here I installed a rocket mass heater.  Several, actually, in several buildings.   

At the same time, i have visited with a lot of people who have racked up years with a conventional wood stove and then switched to a rocket mass heater.  One case:


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## bholler (Nov 6, 2017)

And honestly after watching that video it makes me doubt you claims even more.  There was an absurd amount of disinformation about wood stoves in it and no real discussion of efficiency of rocket mass heaters


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## paul wheaton (Nov 6, 2017)

bholler said:


> And honestly after watching that video it makes me doubt you claims even more.  There was an absurd amount of disinformation about wood stoves in it and no real discussion of efficiency of rocket mass heaters



Share your list of misinformation.

Are you saying the part about how peter and donkey talked about using testo meters and see an average of 93% efficiency?  And that triggers "no real discussion of efficiency"?  How about the part where these numbers have been verified by more than one third party?


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## bholler (Nov 6, 2017)

I am not wasting any more of my time discussing this with you.  You are making absurd claims about wood stove efficiencies that have no basis at all in reality so why would I believe any of your claims about rocket stoves.


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## paul wheaton (Nov 6, 2017)

I think you are not going to believe anything I say because you choose to not believe anything I say.  And that's fine. 

Others are going to believe it because of the massive body of evidence from those that have chosen to try it and have reported excellent results.  And others still because they have looked up the scientific measurement done and looked up the repeatability from others on those numbers.  

If you are happy with what you have, then by all means, continue to be happy.  This path is not for you.  

This path caught my attention, so I now have a rocket mass heater in my house, another in my shop, another in my garage/pantry, another outside, one in a tipi, one in an experimental log structure, one in a tiny cabin near my house (for guests), one in an even tinier cabin on skids (also for guests), one in my backyard that is also a smoker, plus a rocket oven, a rocket kiln, two rocket hot water heaters and two indoor rocket cookstoves (one of which just came online today).   A total of fifteen contraptions using these general designs.   And that's just at my place.

There are the global experts that have traveled from as far away as australia, the netherlands and alaska to be here for our gatherings.  And the students from israel, the check republic, borneo, mongolia and more.   There are the hundreds of people I have visited with about their successes.  

We are all bonkers about rocket mass heaters.  So I guess this path is for us.  And just because we are having a great time does not imply that this path is a fit for you.

It does seem that some folks here have some questions, so I am trying to help.


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## georgepds (Nov 6, 2017)

I'd like to see a better discussion of efficiency, the bit of 1/10 the wood is hard to believe. Just how big is your house that it takes 6 chords to heat (10*0.6)  with a wood stove? I heat mine with 2 chords and a soapstone stove.

.. thanks for the info


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## electrathon (Nov 7, 2017)

How hard is it to start the draft when the stove is cold?  The sideways up and down direction seems like it could be tough.


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## paul wheaton (Nov 7, 2017)

georgepds said:


> I'd like to see a better discussion of efficiency, the bit of 1/10 the wood is hard to believe.



We start with very little wood being used for folks to be very comfortable.   And the large body of anecdotal evidence from people that have shifted from a conventional wood stove to a rocket mass heater.   Years ago, the claims averaged "one eighth the wood" but more recently (from design improvements) people have been sharing "one tenth the wood".  

There have been hundreds of discussions on how and why.  At the top of the list is simply exhaust temperatures for rocket mass heaters are much lower - we are keeping more heat inside.  

There are a few dozen more items, and let's skip past the stuff about conductive and radiant heat and focus just on convective heat.  

A few people in our community insist that a lot of it has to do with the temperature differential.  A rocket mass heater tends to heat a room much slower than a conventional wood stove.   Some people will run a conventional wood stove to the point that it is over 80 in the house - 10 degrees warmer than "minimal winter comfy".  This creates a greater temperature differential between what is inside and outside.  The greater the differential, the more heat will be leaking outside.

Next up is the part where people will do things to try to get the fire to go all night.   This usually leads to the stove running inefficiently.   And as is pointed out in the first video, if the dampers are open, then when the fire goes out, your convective heat is taken outside.

So, a 75% wood stove is actually 59% efficient and is typically operated at 35% efficiency at best, 3% efficiency overnight and in rare cases, negative efficiency as the fire is out and the residual convective heat is being carried outside.   A rocket mass heater typically operates at 93% efficiency (on average).  

So it isn't just one thing.   It's a list of things.  And this, is the beginning of the list.  




> Just how big is your house that it takes 6 chords to heat (10*0.6) with a wood stove? I heat mine with 2 chords and a soapstone stove.



This is a 1300 square foot double wide.  The insulation is not great, and I really need to add a an enclosed front porch and winter curtains.  

The rocket mass heater I have is designed to be "easy to use" instead of "efficient".   So a few design changes would probably get me to less than half a cord.  

And this is montana.   And last year was a colder than average winter.   Not that we hit any record lows, but that we spent a lot more time below freezing than most winters.


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## paul wheaton (Nov 7, 2017)

electrathon said:


> How hard is it to start the draft when the stove is cold?  The sideways up and down direction seems like it could be tough.



It depends on the stove and what the indoor temperature is and what the outdoor temperature is.  

If the rocket mass heater design is "easy to use" it will probably be easy to start.  If it is designed to be more efficient, then it could be picky and people have tricks to help it through the first fire of the season.


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## bholler (Nov 7, 2017)

paul wheaton said:


> We start with very little wood being used for folks to be very comfortable.   And the large body of anecdotal evidence from people that have shifted from a conventional wood stove to a rocket mass heater.   Years ago, the claims averaged "one eighth the wood" but more recently (from design improvements) people have been sharing "one tenth the wood".
> 
> There have been hundreds of discussions on how and why.  At the top of the list is simply exhaust temperatures for rocket mass heaters are much lower - we are keeping more heat inside.
> 
> ...


You really need to learn more about modern wood stoves if you are going to be comparing the two most of us do not struggle at all to burn overnight in fact most of us don't do anything differently at all for overnight.  So your claims of reduced efficiency are invalid.  And there is no way it should ever take 6 cord to heat a 1300 square ft house in Montana with a modern wood stove.  I would expect 3 at most.


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## paul wheaton (Nov 7, 2017)

bholler said:


> You really need to learn more about modern wood stoves if you are going to be comparing the two most of us do not struggle at all to burn overnight in fact most of us don't do anything differently at all for overnight.  So your claims of reduced efficiency are invalid.  And there is no way it should ever take 6 cord to heat a 1300 square ft house in Montana with a modern wood stove.  I would expect 3 at most.



earlier you said "I am not wasting any more of my time discussing this with you. " - I take it you changed your mind?  

Are you saying that your wood stove is "conventional"?  And the the woods stoves favored on these forums are "conventional"?  

My guess is that your wood stove is somehow better than conventional.  And that most of the stoves discussed here are better than conventional.  

At the same time, I would think that if you switched from whatever wood stove you have now to a rocket mass heater designed for efficiency (rather than ease of use) that you would probably be just as comfortable in the same structure with one fifth the wood.   Pure speculation on my part, based on visits with a lot of people that had some good skill at wood heat with a fancy wood stove that made such a transition.


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## electrathon (Nov 7, 2017)

@paul wheaton What is the primary difference to a stove designed for efficiency and one designed for ease of use?


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## paul wheaton (Nov 7, 2017)

electrathon said:


> @paul wheaton What is the primary difference to a stove designed for efficiency and one designed for ease of use?



There can be a few things.  Plus there have been quite a few interesting innovations over the last four years or so.  But I would say that the #1 thing is how much heat you allow up the vertical exhaust.  

A youtube channel person came by my house last fall and took this video.  You can see that the vertical exhaust is quite close to the barrel.   So rather than trying to keep my exhaust temp under 100 degrees (which is what an efficient system would do) I'm hitting about 140 to 150.   So my vertical exhaust ends up being a tertiary thermosiphon.


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## georgepds (Nov 7, 2017)

I want to talk about efficiency a bit, and the perception of heat. I know in my house when it's 72 with the heat pump on , you wear a sweater, when it's 72 with the soap stone stove on , you strip to your skivies. A bit of an exaggeration, but it points to the perception of heat. A radiative surface , like a hot stove, just warms up every solid object in the vicinity.. including you. 

The rocket mass heaters have a very large radiative surface that covers the horizontal exhaust pipe ( not to mention the drum itself) .. sometimes it's a couch, and sometimes it's a bed. If you sit on that massive hot object that holds the heat, you are going to feel warm .. warmer than a room with equivalent air temperature but no hot objects in it . Think of that seat heater in a Chevy Volt

Now a wood stove has more radiation than a heat pump ( but you'll never sit on it) , and a large warm mass has (perhaps) more radiation  than a wood stove. In any event, making your bed on the hottest thing in the room (even if the room is  a TeePee), is just going to make you feel warm. ( I can feel my bum tingling now, just thinking about it)

We need an ASHRE guy to chime in


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## paul wheaton (Nov 7, 2017)

radiant heat is more efficient than convective heat.  And conductive heat is more efficient than radiant heat.

If we can mysteriously convince people to stay in contact with the warm surface of a rocket mass heater to continually harvest the conductive heat, I think it is possible to express that the people of the house could be heated with one hundredth of the wood.   But ...  it is quite rare for that to be even remotely the case.  

But when people are warmed through radiant or conductive heat, the air temperature can be quite low and the people feel "too warm".


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## bholler (Nov 7, 2017)

paul wheaton said:


> earlier you said "I am not wasting any more of my time discussing this with you. " - I take it you changed your mind?
> 
> Are you saying that your wood stove is "conventional"?  And the the woods stoves favored on these forums are "conventional"?
> 
> ...


Nothing fancy at all just a 10 year old recency 3100.  The same stoves you guys are talking about in the 70 to 80% range.  It seems you are comparing to old non secondary combustion stoves which havnt been on the market in years and are in the 20 to 30% range.  Like I said you need to learn allot more about modern wood stoves before you can compare them.


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## SuperJ (Nov 7, 2017)

georgepds said:


> I want to talk about efficiency a bit, and the perception of heat. I know in my house when it's 72 with the heat pump on , you wear a sweater, when it's 72 with the soap stone stove on , you strip to your skivies. A bit of an exaggeration, but it points to the perception of heat. A radiative surface , like a hot stove, just warms up every solid object in the vicinity.. including you.
> 
> The rocket mass heaters have a very large radiative surface that covers the horizontal exhaust pipe ( not to mention the drum itself) .. sometimes it's a couch, and sometimes it's a bed. If you sit on that massive hot object that holds the heat, you are going to feel warm .. warmer than a room with equivalent air temperature but no hot objects in it . Think of that seat heater in a Chevy Volt
> 
> ...



This is all true, and some good points.  I work in HVAC controls can definitely attest to the fact the people are satisfied with much lower ambient room air temperatures when the room is heated thru radiant floor heating.  With a generic RTU people often want 72F or higher to make the complaints stop, but with a infloor heat sometimes mid to high 60's is totally ok. 

I agree with Bholler too, that the 10:1 extreme is probably with some old cobbled together non secondary system run with poor wood, under poor control, to a best case scenario rocket mass.

But, I do have a coworker with an Austrian version of a rocket mass heater who has since substantial reduction in his wood consumption.  In his case it has been about a 30% reduction (10 cords to 7 cords) over the last couple years, but he still runs a wood stove and makes maple syrup with wood so his experience is anecdotal.

Nevertheless, I think it's a great discussion on a different style of wood burning heater.  It would be a shame to see it completely derailed over the specific numbers.


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## bholler (Nov 7, 2017)

SuperJ said:


> This is all true, and some good points.  I work in HVAC controls can definitely attest to the fact the people are satisfied with much lower ambient room air temperatures when the room is heated thru radiant floor heating.  With a generic RTU people often want 72F or higher to make the complaints stop, but with a infloor heat sometimes mid to high 60's is totally ok.
> 
> I agree with Bholler too, that the 10:1 extreme is probably with some old cobbled together non secondary system run with poor wood, under poor control, to a best case scenario rocket mass.
> 
> ...


And I can believe numbers like that.  I agree it is a very valid concept with allot of promise but the experts spouting completely unrealistic numbers doesn't help them forward the concept at all.


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## maple1 (Nov 7, 2017)

0.6 cords of pine is around 15MBTU. Spread that over half a year and it's 50,000btu/day assuming 100% efficiency. That is very little heat load. There is only so much heat in a certain amount of wood - some claims & numbers I'm reading here are rather out to lunch. To suggest it would take 6 cords of wood to heat a place with a wood stove for the winter, that only needs 50,000 btu/day, is kind of out there.


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## georgepds (Nov 7, 2017)

maple1 said:


> 0.6 cords of pine is around 15MBTU. Spread that over half a year and it's 50,000btu/day assuming 100% efficiency. That is very little heat load. There is only so much heat in a certain amount of wood - some claims & numbers I'm reading here are rather out to lunch. To suggest it would take 6 cords of wood to heat a place with a wood stove for the winter, that only needs 50,000 btu/day, is kind of out there.




just for fun.. that works out to be ~14.6 kwh/day


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## maple1 (Nov 7, 2017)

georgepds said:


> just for fun.. that works out to be ~14.6 kwh/day



Which is only a small 1000 watt resistance heater running for 14 hours a day.

I have no doubt they are efficient units, but they aren't magic.


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## georgepds (Nov 7, 2017)

Doesn't seem like it's enough to heat a double wide through a Montana winter.. and that little electric heater is 100% efficient.

Anyone care to do a manual j calculation... just where is that ASHRE expert?


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## paul wheaton (Nov 9, 2017)

In my first post I said "I am not one of the top five brains in rocket mass heaters, but I think I might make the top ten list".  And there were a lot of questions about numbers, efficiency, etc.   So I present Peter van den Berg - definitely in top 3.  Arguably, the top guy.   Maybe the numbers he mentions here will quench some of the curiosity expressed here?


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## georgepds (Nov 9, 2017)

Thanks

Couldn't help notice the wool cap,flannel shirt, and turtleneck... the stove must have been off 


Do you know what device he used to measure co? Saw several lines on the graph but couldn't make out what they mean


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## paul wheaton (Nov 9, 2017)

I think the stove was running (down to a few coals), but Peter was outside working in freezing temps when we asked him to come in for this bit of video.  Plus, we are in the shop and a lot of that day the shop doors are wide open as a couple of dozen people were coming and going.   This was in the middle of our "innovators event" and I think there were five builds happening simultaneously.


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## bholler (Nov 9, 2017)

paul wheaton said:


> I think the stove was running (down to a few coals), but Peter was outside working in freezing temps when we asked him to come in for this bit of video.  Plus, we are in the shop and a lot of that day the shop doors are wide open as a couple of dozen people were coming and going.   This was in the middle of our "innovators event" and I think there were five builds happening simultaneously.


I would still like to know what stoves you are comparing to that you can save 10 times the wood.  What type of burn technology are you comparing your stoves to?


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## electrathon (Nov 9, 2017)

@paul wheaton   Again, I really like the concept here.  I would love to see some information that is not just anecdotal.  People sitting in a room talking about the stove feels warm and fuzzy, but specific drawings and design layout would be very helpful.   I still don't see how you can get the draft started when the stove is cold (or reverse drafting).  A wood stove with a stack going up can be hard enough, your stove goes up, down, sideways and then up.  Once it is pulling it makes since, I am curious about starting it without flooding the house with smoke.  What keeps fly ash out of the main heating chambers?  The turbo action should be drawing a lot of ash forwards and into areas that are not really accessible.  Combustion chamber and orifice size will make or break this concept, even the angle could affect the burn.  Details would help.


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## Woodsplitter67 (Nov 9, 2017)

To answer the op... i dont want a rocket mass heater because... i love the stove i have.. it looks prettier... my stove is very efficient to begin with.. and lastly i wouldn't one in my living room...


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## bholler (Nov 9, 2017)

paul wheaton said:


> In my first post I said "I am not one of the top five brains in rocket mass heaters, but I think I might make the top ten list".  And there were a lot of questions about numbers, efficiency, etc.   So I present Peter van den Berg - definitely in top 3.  Arguably, the top guy.   Maybe the numbers he mentions here will quench some of the curiosity expressed here?



The only numbers he gave were for a 5 min period of a burn for co emissions.  If you want to convince us of anything you are going to have to give us some real efficiency numbers compared to a modern woodstove using the same fuel and testing procedures.  

He mentioned that there is no smoke.  On any modern woodstove if it is being run correctly there will be no smoke either.


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## georgepds (Nov 9, 2017)

Woodsplitter67 said:


> To answer the op... i dont want a rocket mass heater because... i love the stove i have.. it looks prettier... my stove is very efficient to begin with.. and lastly i wouldn't one in my living room...




I used to want a masonry stove ( a rocket mass stove is close to a masonry one). Once I got a modern soap stone stove, I was content, and the desire to fill my life with extra large hot stone objects went away, except for the soapstone stove

I'm interested in low wood use, but  I find the numbers for the rocket hard to believe. I do not doubt the enthusiast impression/ experience that it works well, but there is a big difference between works well and ten times better. I'm with @bholler I'd like to see less squishy numbers , and better description of what is being compared. Is it 10x better than an open fire? probably. Is it 10x better than a modern EPA stove? Until I see the test data, my guess is probably not.


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## georgepds (Nov 9, 2017)

Wood stove

For those who like details I found a technical article describing wood stove emission measurements. The two stoves tested measured 77% and 79% efficient,  comparable to EPA stoves

It is physically impossible to be 10 times better with any device that is not a heat pump To be 790% efficient you are no longer extracting heat from wood, but using the energy to run a heat pump, and that is not what a Rocket mass stove does

Anyway here us the link to stove testing article

http://www.sciencedirect.com/science/article/pii/S187661021403481X


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## RobbieB (Nov 9, 2017)

I agree.  It is easy to be 10X open fire efficiency 80% vs 8%, but not a modern stove which is already 70-80%


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## electrathon (Nov 9, 2017)

RobbieB said:


> I agree.  It is easy to be 10X open fire efficiency 80% vs 8%, but not a modern stove which is already 70-80%


I think the squishy math works like this (from what I have been able to read and see online).  Modern stove 80% efficient at full raging burn.  A few hours later it is stepping back to 50%  By six hours into the night it is at 20%  By morning the fire is out, stove is cold and the draft is pulling, negative 5%. 

Enter the rocket stove with LOTS of biomass.  Starts out raging at 85% for 30 minutes.  Fire goes out and you have mass storage heat for 6 house, 400% efficient factoring that part in.  8 times or so more efficient, depending on your exact numbers.

I think Paul Revere heard similar discussions when he welded together a bunch of plate steel and built a box in the middle of the room instead of a raging fire in the fireplace.  Common since said if a stove worked better than a fireplace we would have been using them thousands of years earlier.


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## bholler (Nov 9, 2017)

electrathon said:


> I think the squishy math works like this (from what I have been able to read and see online).  Modern stove 80% efficient at full raging burn.  A few hours later it is stepping back to 50%  By six hours into the night it is at 20%  By morning the fire is out, stove is cold and the draft is pulling, negative 5%.
> 
> Enter the rocket stove with LOTS of biomass.  Starts out raging at 85% for 30 minutes.  Fire goes out and you have mass storage heat for 6 house, 400% efficient factoring that part in.  8 times or so more efficient, depending on your exact numbers.
> 
> I think Paul Revere heard similar discussions when he welded together a bunch of plate steel and built a box in the middle of the room instead of a raging fire in the fireplace.  Common since said if a stove worked better than a fireplace we would have been using them thousands of years earlier.


The problem is that those numbers are not the least bit accurate if you have a good modern stove that is run correctly.  The lesson to be learned is that if you make up fake numbers for the other guy it is really easy to beat them.  

I really think that it is a promising technology that could work for some people.  But they need to be realistic with their numbers if they want to be taken seriously.


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## georgepds (Nov 9, 2017)

Here is a good discussion on system efficiency. They distinguish between combustion efficiency (% of energy extracted from wood) and transfer efficiency (%of energy transferred to the room)

The basic idea is rocket mass heaters are better than wood stoves because the transfer efficiency is so high

https://permies.com/t/55938/rocket-mass-heater-works-efficiently

Sfaik, The claims about transfer efficiency are not based on measurements


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## georgepds (Nov 9, 2017)

electrathon said:


> I think the squishy math works like this (from what I have been able ...
> 
> I think Paul Revere heard similar discussions when he welded together a bunch of plate steel and built a box in the middle of the room instead of a raging fire....



I think that was Ben Franklin



1728: Cast iron stoves begin to be made in quantity in the US. These first stoves of German design, are called Five-plate or Jamb stoves.



1744: Benjamin Franklin develops his own cast iron stove design. His Pennsylvania fireplace surpassed the efficiency of other inventions, and is still a popular heating stove today.
1763: Frederick the Great of Prussia stages a competition for a "room stove which would consume the least wood".


1772: David Rittenhouse added an 'L' shaped chimney to the Franklin Stove to prevent smoke from venting into the room. His design is what is known as a "Franklin Stove" today.


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## bholler (Nov 9, 2017)

georgepds said:


> Here is a good discussion on system efficiency. They distinguish between combustion efficiency (% of energy extracted from wood) and transfer efficiency (%of energy transferred to the room)
> 
> The basic idea is rocket mass heaters are better than wood stoves because the transfer efficiency is so high
> 
> ...


That is the problem they bash the woodstove numbers as being inaccurate.  Yet they don't provide hard numbers of their own.


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## electrathon (Nov 9, 2017)

georgepds said:


> Here is a good discussion on system efficiency. They distinguish between combustion efficiency (% of energy extracted from wood) and transfer efficiency (%of energy transferred to the room)
> 
> The basic idea is rocket mass heaters are better than wood stoves because the transfer efficiency is so high
> 
> ...


That is a good explanation, sort of what I was thinking, only smarter.


georgepds said:


> I think that was Ben Franklin


Yea, him.  But my answer was more funny.


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## Heftiger (Nov 9, 2017)

electrathon said:


> I think the squishy math works like this (from what I have been able to read and see online).  Modern stove 80% efficient at full raging burn.  A few hours later it is stepping back to 50%  By six hours into the night it is at 20%  By morning the fire is out, stove is cold and the draft is pulling, negative 5%.
> 
> Enter the rocket stove with LOTS of biomass.  Starts out raging at 85% for 30 minutes.  Fire goes out and you have mass storage heat for 6 house, 400% efficient factoring that part in.  8 times or so more efficient, depending on your exact numbers.
> 
> I think Paul Revere heard similar discussions when he welded together a bunch of plate steel and built a box in the middle of the room instead of a raging fire in the fireplace.  Common since said if a stove worked better than a fireplace we would have been using them thousands of years earlier.



You’re giving 400% credit for the heat storage in the biomass, but not giving any credit to the biomass heat storage of the wood stove. My cast iron jacketed stove continues to be warm after the fire is out.


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## electrathon (Nov 9, 2017)

Heftiger said:


> You’re giving 400% credit for the heat storage in the biomass, but not giving any credit to the biomass heat storage of the wood stove. My cast iron jacketed stove continues to be warm after the fire is out.


I just guessed at numbers that I think is how they come up with the huge efficiency variations.


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## RobbieB (Nov 9, 2017)

My nat gas furnace is 95% efficient.  It's a modern condensing unit that needs a draft inducer, a condensate collection trough and extracts so much heat that the flue is 2 inch PVC pipe.  Now that's pretty good extraction, but not the best.  The modulating units will hit 98%.

But the old (non condensing) units ran at 80%.  I am amazed that modern wood stoves can hit this.

And you are comparing blower driven transfer to "hot rock" storage and I imagine that few people really want a big stack of hot rocks in the middle of their house.  

Maybe good for cavemen.


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## georgepds (Nov 10, 2017)

Here is an example of rocket mass heater math.... explains a bit how they get their numbers... they assume woodstove efficiency is really 3% to 15%

https://www.richsoil.com/wood-heat.jsp#efficient-heat

"First, "75% efficient" isn't really 75% efficient. 16% is allowed for heat going up the chimney, so it is actually 59% efficient. And that was from the best burn in a lab under optimal conditions. An excellent operator might be able to get about 35% efficiency. Most people run their "75% efficient wood stove" at 3% to 15% efficiency."



To me this is gobbledygook.. how do they know most people operate at so low efficiencies?


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## bholler (Nov 10, 2017)

I also have to question the wood around their thermal masses.  I heard several times that the thermal mass is uncomfortable to touch.  That could easily mean it is into pyrolysis teritory. Wood is also pretty close to the burn chamber on both example we see in the videos.


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## peakbagger (Nov 10, 2017)

Funny thing is the world most efficient "wood stove" (most folks would call it a boiler)was designed and sold 35 years ago. It was a short burn very high temperature combustion that put out little or no emissions mostly water vapor. The major difference was that the designer developed it for space heating a conventional home so it used water for thermal storage instead of masonry. http://people.umass.edu/dac/projects/Hills_Furnace/Hills_Furnace.html. There are a few Jetstream owners on Hearth. Tom In Maine a member of hearth has designed and built a similar unit that uses pellets for fuel but due to the cost of certification and production he is unable to sell it commercially. (he worked with Dick Hill for years).

FYI few folks like to talk about NOx emissions, burn hot and fast like a rocket stove and NOx goes way up but CO goes down. The only way to keep NOx down is staged combustion or put in ammonia injection and NOx catalysts.


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## maple1 (Nov 10, 2017)

Too bad they have to make up smoke & mirrors numbers to try to make 'the others' look bad, in order to try to make 'their own' look better. As I said before I am sure it is a very efficient unit but the comparison claims being put forward are just silly stupid wrong. I am willing to bet that if this heater can heat this double wide on 0.6 cord, a properly sized and installed wood stove would burn no more than 2 cord, at the very most, all else being equal, and being generously estimated in favor of the rocket. And the home would likely be warmer.

One simple thing I would be curious to see is flu pipe or chimney temp readings on one of these units both through an entire burn and also through an entire 'coasting' session when the fire is out. Should be an elementary exercise but I haven't seen any flue temp data at all yet - but I have not searched for it. I would think it would be readily available and posted already in this thread if it was there. I am sure there is some heat leaking up the chimney after the fire goes out - which is kind of an efficiency hit. My storage tanks only leak heat within the building envelope after my fire is out - they don't have a pipe to the outdoors.


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## NateB (Nov 10, 2017)

What is the cleaning schedule for a rocket thermal mass stove?  And how often do you have to replace the exhaust pipe?


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## maple1 (Nov 10, 2017)

NateB said:


> What is the cleaning schedule for a rocket thermal mass stove?  And how often do you have to replace the exhaust pipe?



..and how do you clean it?


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## georgepds (Nov 10, 2017)

Here is a screen grab of Peter Berg's measurements. I get the impression efficiency (red %n)  is deduced from ppm CO, %O2, and temperature deg F.  I'm reading %n as efficiency, but this may be incorrect, he does not identify the axis otherwise.

My understanding is efficiency is deduced from the other measurements. If any one knows how this is done, or can point me to a reference,  please let me know (*).. The science direct articles notes _"The purpose of the performance analysis was to determine the combustion efficiency and the losses associated with different batches of the combustion tests. The efficiency of the wood stoves was calculated as described in the European standard EN 13229 that takes thermal, chemical and radiation heat losses into consideration [12]. The thermal heat loss is calculated on the basis of the temperature difference between the flue gas and indoor air with the specific heat of the flue gas. The chemical heat loss is calculated from the CO and CO2 concentrations of the flue gas. Radiation heat loss is taken as 0.5 % according to the standard."_

(*) I looked up EN 13229, and it costs $166, so i'm looking for cheaper info)


If the science direct article is correct, Peter's graph is missing the needed CO2 concentration for the efficiency calculation ( He may have measured it and just not posted it, remember we are comparing a peer reviewed paper from science direct to Peter talking on you tube, the documentation requirements are different) . The other thing to note is the Belgian stove paper computes efficiency over the batch burn, Peter seems to do it continuously)

The temperatures are so low they must be at the chimney outlet , though this is not stated , though the science direct paper on Belgian stoves  states it is 1.8 m above the stove

Also attached is a screen grab from the science direct article on the high efficiency Belgian stoves (_"The flue gases were sampled by the steel probes from the stack at about 1.8 m above the stoves." _This may account for the differences, the RMH has the outlet buried in the couch)

IIRC,  Somewhere in his presentation Peter notes that the CO concentration for the RMH  is less than 5 ppm, and that is notable. But, my reading of the Belgian stove graph is the
concentration is often less than 5 ppm in the middle of the burn.  Comparing the two graphs it looks like the Belgian stoves have high CO at the beginning of the burn, whereas the RMH achieves a low value fast. At the end of the burn the increase in CO seems compareable ( a slow steady rise to about 7 for the Belgian stove and about 10 for the RMH)

No good conclusions here.. just more wood for the fire










(*) I looked up EN 13229, and it costs $166, so i'm looking for cheaper info. I found an article by Petrocelli ** who shows how to do it.. but it will take a closer read



**  http://iopscience.iop.org/article/10.1088/1742-6596/655/1/012021/pdf


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## maple1 (Nov 10, 2017)

I'm not sure how you could accurately measure overall efficiency. With a boiler, you can get it pretty close by measuring water flow, and temps in & out over the course of a burn. Not sure how you can accurately measure how much heat gets transferred into the heat sink to be released later? Given its size and what would likely be unequal transfer throughout.


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## paul wheaton (Nov 12, 2017)

In 2008 I was heating my home with the wood stove pictured above.  A guy was sitting at my kitchen table telling me about rocket mass heaters.   For the first 20 minutes it just sounded like he had to be on drugs or something.  None of it added up.   But he was a really sharp guy, and I knew him reasonably well, so it didn't seem like the sort of thing he would make up, or exaggerate.   In time I became curious enough that I bought a ticket to a rocket mass heater workshop in january of 2009. 

The things I saw, heard, felt and learned turned my wood heat world upside down.  

We built a rocket mass heater in about a day.  In the evenings, we used the existing rocket mass heaters.  There was snow on the ground outside and all of the houses were very drafty.  Single pane glass with gaps around the edges.   The doors were made from a single layer of wood with gaps all around the doors.   The concept of "weatherstripping" wasn't even considered in this place.  

So very different.  

One big thing was that rather than measure the difference in burn efficiency, the metric was cords of wood from the wood shed.  

There are certainly downsides/tradeoffs - so it isn't perfect, and it isn't a slam dunk.  But you do heat a home with very little wood.  

And a lot of the details don't fit into your head until you actually see it and maybe run one for a day or two.  Or, at least, that's the way it was for me and I suspect that it will be this way for others.  

When I first heard about rocket mass heaters, I struggled to understand the stuff about how the fire burns sideways (and sometimes upside down).   So I tried to find video or pictures on the internet.   Nothing.   So at that january, 2009 event, I took video and pictures and posted what I saw.  

I bought land and one of the very first things I did was have a rocket mass heater workshop where we built a rocket mass heater in a tipi.  







A couple stayed there the first winter.  They woke up one morning, got out of bed, changed their clothes and went outside to where it was 26 degrees below zero (F).  The fire went out the night before at about 9pm.   When they changed their clothes they said it felt like 50 or 55.  You have to go by "felt like" because a thermometer would measure air temperature without regard for radiant or conductive heat. 

This is where it is really different.  

And when I carefully measured how much wood I used in my house last winter, I made sure to carefully document a thermometer around the corner so it would be measuring ONLY convective heat.  

It is different.  Really different.  Amazingly different.   Wonderfully different.  

People are typically MORE comfortable with (typically) one tenth the wood.   It seems there are about six factors that people have come up with on how this can be.  I suspect that the math and the body of evidence will become more significant over the next ten years.   For now this path has been about nine years long and I have seen interest in rocket mass heaters grow exponentially.  And the quality of the final product has grown exponentially also.  










At the innovators event this year, there were some new designs and improvements on old designs.   This whole field has a HUGE area for optimization.   I think we are just getting started.

I suspect that most of you will ignore it for several years, but a few of you will go out of your way to see one and maybe even build one in the next year.  Maybe, in time, even become the person that puts together the numbers to make folks more comfy.


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## paul wheaton (Nov 12, 2017)

> I still don't see how you can get the draft started when the stove is cold (or reverse drafting).



There is an insulated chimney in the barrel.  It is about four feet tall.  We call it "the heat riser".  When starting a rocket mass heater, you must prime it.  Different folks prime it in different ways.   I usually put some paper under it and then ignite the paper.  While the prime is burning, I add the rest of my paper and kindling to start the rest of the fire.  

Once the heat riser is primed, we have a pretty good push in the right direction.




> What keeps fly ash out of the main heating chambers?



Nothing.  Which is why we have cleanouts.   We clean out the fly ash about once a year.




> To be 790% efficient you are no longer extracting heat from wood, but using the energy to run a heat pump, and that is not what a Rocket mass stove does



We usually see efficiency of about 93%.  Sometimes more, sometimes less.   

And, we are more comfortable with one tenth the wood.   

Therefore, the numbers from the woodshed are not dependent on the efficiency of the burn alone.  There is a richer story.  




> I really think that it is a promising technology that could work for some people. But they need to be realistic with their numbers if they want to be taken seriously.



And these are our numbers.    And a few of you will look into and decide to try it out.   And then they will report similar numbers. 

Those of us that have taken the leap are very happy.  And when we share our enthusiasm, it is as frustrating to us as it is to you.

Maybe over the winter you will find yourself visiting somebody that has one and you can experience it for yourself.


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## paul wheaton (Nov 12, 2017)

> One simple thing I would be curious to see is flu pipe or chimney temp readings on one of these units both through an entire burn and also through an entire 'coasting' session when the fire is out.



The super efficient rocket mass heaters have an exhaust temp of about 70 to 120 while burning.   The easy to use rocket mass heaters are closer to 90 to 160.

When the fire goes out, the barrel acts a bit like an upside down p-trap, stopping/slowing the air from continuing to move through the system.


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## paul wheaton (Nov 12, 2017)

> What is the cleaning schedule for a rocket thermal mass stove? And how often do you have to replace the exhaust pipe?



We typically need to clean out ash from the burn tunnel daily or once a week.  But we pop off the barrel and open the access panels about once a year to clean out ash.

The oldest rocket mass heater still running is over 20 years old.   My understanding is that nothing has needed to be replaced yet.


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## paul wheaton (Nov 12, 2017)

> The temperatures are so low they must be at the chimney outlet , though this is not stated , though the science direct paper on Belgian stoves states it is 1.8 m above the stove



Every time I have seen the testing performed, they have drilled a hole into the exhaust about five feet up from ground level.  Once in a while I have seen people test the exhaust at the roof, but that seems to be more the exception than the rule.


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## paul wheaton (Nov 12, 2017)

> Given its size and what would likely be unequal transfer throughout.



This is where the cob mass really shines.   Because of conductive heat, the heat starts off spotty, but once the fire is out, the heat continues to move through the mass with conduction and ends up pretty even all over.


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## electrathon (Nov 12, 2017)

On the stoves in the pictures, does the wood burn in the hole near to the metal drum?  Where is the door to put in a prime fire to start the draft? 

Why is Cobb the choice for building these?  Is it because it is cheap and available?  It seems that a stone slab outer surface filled with small stone chips would be a better heat mass storage product.  A stone stove surface would look pretty.  Many of these stoves look like they were built by the Indians a few hundred years ago.  Except of course that a 55 gallon drum seems to be a product of choice.  It seems that loosing that for a stone heat chamber or if metal is needed a stainless barrel could be easily made that was far more attractive.  A lot of the objections I see are related to the appearance of the cobbled together designs.


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## paul wheaton (Nov 12, 2017)

Here is a still from my dvd set






This is a style that I invented called "pebble style".  Rather than cob, the mass is filled with pebbles.  So a different aesthetic.  A wood box with a granite top.  Pretty much exactly what you are suggesting.

Some alternatives to the barrel:
















And from this year's innovators event that just wrapped up a few weeks ago, here is the "cyclone rocket mass heater" for a tiny house.   It has no barrel:


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## bholler (Nov 12, 2017)

paul wheaton said:


> There is an insulated chimney in the barrel.  It is about four feet tall.  We call it "the heat riser".  When starting a rocket mass heater, you must prime it.  Different folks prime it in different ways.   I usually put some paper under it and then ignite the paper.  While the prime is burning, I add the rest of my paper and kindling to start the rest of the fire.
> 
> Once the heat riser is primed, we have a pretty good push in the right direction.
> 
> ...


So again what stoves are you comparing to when you come up with the 10x number?

How is that stove being run and with what fuel?

You just keep giving us feel good stories but really hanvt given us any real info at all.

And i have a very serious safety question what is the max temp that wood is exposed to that is surrounding your thermal mass.  If the top is hot enough to be uncomfortable to touch it is to hot for wood to be in contact with it.


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## georgepds (Nov 12, 2017)

OK I don't know why, but this pic gives me 70's flashbacks..

Hum with me

"Gimme head with hair
Long beautiful hair
Shining, gleaming,
Streaming, flaxen, waxen

"Give me down to there hair
Shoulder length or longer..








OK I do know why.. it's the yurt and the yoga mats and the strong whiff o smug.. They seem to be thinking  "Just where did I put my chakra" 

What are those holes near the drum?? Gopher holes? I take it the drum is the point of this pic in a wood stove thread. If so, you buried the lead.  The visual message is "you too can have a flat belly and a healthy 20 something companion", if only you get your own RMH


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## twd000 (Nov 12, 2017)

Matt Walker is another rocket mass heater designer that I have a lot of respect for.
http://walkerstoves.com/index.html

We had a good exchange in this thread about the woodstove decathlon : http://donkey32.proboards.com/thread/1908/woodstove-decathalon-washington?page=2
His takeway , based on running both types of stoves side-by-side for a week, was that a modern catalytic stove (Blaze King, Lopi, Woodstock) had equal or better overall efficiency than the best current RMH designs, with slightly lower emissions. 

If inquisitive people continue innovating on the RMH design, I would not be surprised if they catch up to steel stoves. You never know where the next great idea will come from.


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## maple1 (Nov 12, 2017)

Catch up? They're already 10 times better.


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## paul wheaton (Nov 13, 2017)

twd000 said:


> Matt Walker is another rocket mass heater designer that I have a lot of respect for.
> http://walkerstoves.com/index.html
> 
> We had a good exchange in this thread about the woodstove decathlon : http://donkey32.proboards.com/thread/1908/woodstove-decathalon-washington?page=2
> ...



That was two years ago.  Matt is still doing a huge amount of work in the world of rocket mass heaters.  

If you wish to measure just in terms of efficiency of the stove and are not concerned about what happens in the woodshed, then go for it.  I think Matt and the other rocket mass heater folks are looking at what is happening in the woodshed and continuing to focus on rocket mass heaters.



I very carefully measured the wood used in our rocket mass heater last winter.   0.60 cords of wood on a particularly cold winter.   I think that with a few modifications and a warmer winter, I could get that down to 0.35 cords of wood.  


And if you don't believe my numbers, cruise the internet and find the experiences of others.  And now that the idea is in your head, it is possible you will mention it to somebody in the next month or two and find yourself visiting with somebody that put one in and can tell you their experiences.


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## bholler (Nov 13, 2017)

paul wheaton said:


> That was two years ago.  Matt is still doing a huge amount of work in the world of rocket mass heaters.
> 
> If you wish to measure just in terms of efficiency of the stove and are not concerned about what happens in the woodshed, then go for it.  I think Matt and the other rocket mass heater folks are looking at what is happening in the woodshed and continuing to focus on rocket mass heaters.
> 
> ...


Again what type of stoves are you comparing to when you figure your 1/10th.  Because it makes a huge difference if you are compaing to pre epa stoves or not


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## bholler (Nov 13, 2017)

paul wheaton said:


> That was two years ago.  Matt is still doing a huge amount of work in the world of rocket mass heaters.
> 
> If you wish to measure just in terms of efficiency of the stove and are not concerned about what happens in the woodshed, then go for it.  I think Matt and the other rocket mass heater folks are looking at what is happening in the woodshed and continuing to focus on rocket mass heaters.
> 
> ...


And i would still like to know how you determined the wood is safe where it is.  The fact is as a pro i cannot put one of these in wothout them being spproved in some way.  And the same goes for anyone who will need an inspection or insurance.


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## RobbieB (Nov 13, 2017)

I'll say one thing that strongly favors the mass heaters efficiency claims and I see it here often.

"Help my stove is cooking me out of my house"  And here's the common response "Open the windows"

Now if you are venting all the excess heat to the outdoors you are not too efficient no matter what the stove spec is.

I don't think the rocket mass heater guys suffer this problem.


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## bholler (Nov 13, 2017)

RobbieB said:


> I'll say one thing that strongly favors the mass heaters efficiency claims and I see it here often.
> 
> "Help my stove is cooking me out of my house"  And here's the common response "Open the windows"
> 
> ...


If it is oversized for the house there is no reason it couldnt overheat things.  That issue comes down to sizing the appliace correctly and knowing how to run it for your situation.  For example i just bought a new house and i have had it to warm a few times because i am learning how much heat is needed.  I will have it down after a season and wont have much of an issue.  The difference between the two is with a mass heater if you make to much heat it is going to be to hot for a long time.  While with a stove it will be at most 6 to 8 hours till things cool down


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## georgepds (Nov 13, 2017)

RobbieB said:


> I'll say one thing that strongly favors the mass heaters efficiency claims and I see it here often.
> 
> "Help my stove is cooking me out of my house"  And here's the common response "Open the windows"
> 
> ......



or don't put so much wood in to it


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## Squisher (Nov 13, 2017)

Or enjoy some fresh air. 

I think this stuff looks interesting.....in someone else's home. But I don't see it catching on in any large capacity due to certification/code and insurance as bholler mentioned. To me it seems it will always be a fringe thing, someone is going to have to really want this and be very dedicated to having it. Because a professional company is unlikely to come and Service it or try to inspect it for insurance or safety. 

Wood heating isn't rocket science(see what I did there? he he he).  I am quite comfortable with the amount of wood I use. So that being said why would I ever want some giant questionably attractive heating device in my home?


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## bholler (Nov 13, 2017)

Squisher said:


> Or enjoy some fresh air.
> 
> I think this stuff looks interesting.....in someone else's home. But I don't see it catching on in any large capacity due to certification/code and insurance as bholler mentioned. To me it seems it will always be a fringe thing, someone is going to have to really want this and be very dedicated to having it. Because a professional company is unlikely to come and Service it or try to inspect it for insurance or safety.
> 
> Wood heating isn't rocket science(see what I did there? he he he).  I am quite comfortable with the amount of wood I use. So that being said why would I ever want some giant questionably attractive heating device in my home?


I personally am not willing to give up that massive ammout of space in my home.


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## Squisher (Nov 13, 2017)

Myself either, and homes and decorating are personal preference and not to be insulting but I just don't see this spreading across North America like warmth through a mass heater.

It's good to be enthusiastic about things and that's what it's going to take for someone to do this I think.  I don't think any wood savings and let's be realistic here.  I'm not going to argue that the OP didn't use .6 of a scientifically accurate measured cord to heat his dwelling but could never see that equating to 6 cords using a stove to heat the same space. I just don't see 'wood savings' being a big enough motivator to make someone want something like this over a modern stove.

Stoves are easy peasy. People like easy.


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## twd000 (Nov 13, 2017)

bholler said:


> I personally am not willing to give up that massive ammout of space in my home.



Yes the space requirements , plus the aesthetics of a 55 gallon barrel in the living room, are major barriers to adoption of RMH by your average American

Also recall that the first mainframe computers took up the space of an entire building. "No one will ever want THAT thing in their house"

I could envision a redesign that allows a homeowner to retrofit a fireplace with the mass - either a honeycomb of firebrick splits, or a water storage feature. If the efficiency claims can be emprically proven (same house heated by Blaze King vs RMH for successive seasons) it would provide impetus to drive those innovations


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## bholler (Nov 13, 2017)

twd000 said:


> Yes the space requirements , plus the aesthetics of a 55 gallon barrel in the living room, are major barriers to adoption of RMH by your average American
> 
> Also recall that the first mainframe computers took up the space of an entire building. "No one will ever want THAT thing in their house"
> 
> I could envision a redesign that allows a homeowner to retrofit a fireplace with the mass - either a honeycomb of firebrick splits, or a water storage feature. If the efficiency claims can be emprically proven (same house heated by Blaze King vs RMH for successive seasons) it would provide impetus to drive those innovations


I agree the concept does hold promise. But retrofitting an existing fireplace would not work.  But that doesnt mean goid looking ones could not be made.  

Again i have nothing against the idea as a whole.  I just have problems with people claiming 1/10th the wood useage when they clearly dont know a thing about modern wood stoves.  They are talking about waking up to load the stove and waking up to a cold house.  That simply is not the reality if your stoves is sized properly and run right.


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## RobbieB (Nov 13, 2017)

Yeah, it would be cool to have these designs in new construction and me thinks it could be "traditionally aesthetic" pleasing too.  Not to mention good for masons.

I'm thinking rocket stove with glass front and 2 mass absorber / diffusers either side in the big traditional hearth up to the ceiling.  If well insulated could even be incorporated on outside wall of house.


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## twd000 (Nov 13, 2017)

bholler said:


> I agree the concept does hold promise. But retrofitting an existing fireplace would not work.  But that doesnt mean goid looking ones could not be made.



 What makes you so certain that a fireplace retrofit RMH couldn't be designed? That how insert stoves work, and it has made them adopted more broadly in existing construction situations.


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## bholler (Nov 13, 2017)

twd000 said:


> What makes you so certain that a fireplace retrofit RMH couldn't be designed? That how insert stoves work, and it has made them adopted more broadly in existing construction situations.


There is just to much going on with a rmh and not enough room in a fireplace to do it properly


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## twd000 (Nov 13, 2017)

bholler said:


> There is just to much going on with a rmh and not enough room in a fireplace to do it properly



In the current design, yes. But that won't necessarily be the final design. It's essentially a heat exchanger, you can play with the mass/volume/surface area numbers in an infinite number of combinations to achieve the performance you need. My un-used fireplace has over 12 cubic feet of volume. What if a refractory shop made a honeycomb grid of firebrick cement? Like the grid size of a catalyst, without the platinum. There's your surface area. Plus the hearth, which extends 16" in front, and you could bring mass up to the ceiling.


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## bholler (Nov 13, 2017)

twd000 said:


> In the current design, yes. But that won't necessarily be the final design. It's essentially a heat exchanger, you can play with the mass/volume/surface area numbers in an infinite number of combinations to achieve the performance you need. My un-used fireplace has over 12 cubic feet of volume. What if a refractory shop made a honeycomb grid of firebrick cement? Like the grid size of a catalyst, without the platinum. There's your surface area. Plus the hearth, which extends 16" in front, and you could bring mass up to the ceiling.


I have taken out lots of fireboxes to rebuild them and taken down lots as well.  Very few have a large open space in them to work with.  Most have allot of masonry inside that shell.  In most cases it would be cheaper and easier to take it down and start over.  And at that it would really only work with interior fireplaces.  Which atleast in this area are few and far between.


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## bholler (Nov 13, 2017)

twd000 said:


> What makes you so certain that a fireplace retrofit RMH couldn't be designed? That how insert stoves work, and it has made them adopted more broadly in existing construction situations.


With mass heaters wether it is a rocket or traditional madonry heater you need acess doors to clean all of those passages out.  Integrating them into a pre exisyong structure would be a real pain as well.


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## maple1 (Nov 14, 2017)

I am also very doubtful that a heater you can sit on & lay on will be sending very much heat to the more outer reaches of the structure. It is still a space heater, as is a stove. And some seem to have issues getting the outer reaches of their house warm enough even with surface temps 4x or more than that of a mass heater. Radiant heat is a good thing but it will only radiate so far. Old cast iron hot water or steam rads can be very comfy too but they are a lot hotter, and you need more than one of them in a room of much size.

Should just stick to the efficiency side & claims, rather than trying to convince people they can heat 10x as good as a wood stove or heat to the same level of comfort on 10x less wood. That's where the credibility goes a bit sideways.


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## paul wheaton (Nov 16, 2017)

RobbieB said:


> I'll say one thing that strongly favors the mass heaters efficiency claims and I see it here often.
> 
> "Help my stove is cooking me out of my house"  And here's the common response "Open the windows"
> 
> ...



True.   The temperature change is much slower.  

Along those lines, if you have a couple dozen people over, without a rocket mass heater, you might find that you need to open a window.  But with a rocket mass heater, I will intentionally NOT build a fire when people are coming over.   The house never gets hot.   I think the mass absorbs all that excess heat and then I can go an extra day of not running a fire.   

In a similar vein - in the summer, it is cooler inside.   I think the rocket mass heater absorbs the heat on a hot day and releases it during the cooler evening.


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## paul wheaton (Nov 16, 2017)

> I am also very doubtful that a heater you can sit on & lay on will be sending very much heat to the more outer reaches of the structure.



When I carefully measured last winter and heated with just 0.60 cords of wood, I spent the winter working in my office, out of sight of the rocket mass heater.   So my comfort was based entirely on convective heat - nothing for radiant or conductive heat.  Further, when I monitored the thermometer, it did not have line of sight with the rocket mass heater.   So, again, only measuring convective heat.  

Averaging about 69 degrees through the winter - measuring just convective heat.  

And there is something to be said for the luxuriant feeling of sitting on the bench or sitting on the couch and putting your feet on the warm bench.




> rather than trying to convince people they can heat 10x as good as a wood stove or heat to the same level of comfort on 10x less wood. That's where the credibility goes a bit sideways.



I am cool with you not believing it.   At the same time, we now have techniques to heat a home with one twentieth the wood.  And each year we find a few more interesting optimizations.  

As I mentioned earlier, I have ideas on how I might get my wood usage down to 0.40 or maybe 0.35 cords of wood for a winter.   But that doesn't even take into account some of the things that we have experimented with with bypasses and insulated guillotines.  There is a possibility that I can hit that 69 degree average, through a montana winter, in a 3-bedroom home with 0.25 cords of wood for the winter.     And that is still based on convective heat.   


Here is an experiment I did six years ago with radiant and conductive heat, where I was able to cut 87% off of my electric heat bill.  



I suppose I could either work in these techniques, or I could add a couple more tiny rocket mass heaters into my office and my bedroom - so a few twigs would give me some conductive heat.  

In this video we talk about some other experiments with conductive and radiant heat.  Including a tipi we have here with a rocket mass heater:




I encourage everybody to keep a firm grasp on your skepticism.   And as time passes, I suspect that you will get the opportunity to see one in action and visit with somebody you know an trust that has one.   

It isn't going to be for everybody.   But I think that ten years from now, half the people that burn wood will use a rocket mass heater.


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## edyit (Nov 16, 2017)

paul wheaton said:


> But I think that ten years from now, half the people that burn wood will use a rocket mass heater.



i get that you are really passionate and firmly believe in these heaters but i don't see 1/2 the people that burn switching to them. Heck 1/2 the people that burn don't want to switch to an epa stove let alone a 55 gallon drum and a block of concrete in their house. then there is the insurance aspect. most insurance companies want something that is UL certified and able to pass inspection. I don't know if you're going to get that with this. And lastly, for myself atleast, if i want the house at 69F for heat i'll use the oil furnace...


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## paul wheaton (Nov 16, 2017)

Rocket mass heaters are now in the building codes for several cities and counties.   More coming.   And insurance companies are coming around.

I will be uploading a video in the next couple of days showing a rocket mass heater that has no barrel, or something that looks like a barrel.   We already have hundreds of rocket mass heaters that don't have a barrel.   It just seems that for hundreds of thousands of people, the barrel is not a big deal.

There is one rocket mass heater that is UL certified, and there is work being done on more.  

69 degrees is the average I had here last winter.   It seems I would forget to add to the fire when we got to 73 or so, and I would build a new fire when it got to 66 or so.


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## bholler (Nov 16, 2017)

paul wheaton said:


> Rocket mass heaters are now in the building codes for several cities and counties.   More coming.   And insurance companies are coming around.
> 
> I will be uploading a video in the next couple of days showing a rocket mass heater that has no barrel, or something that looks like a barrel.   We already have hundreds of rocket mass heaters that don't have a barrel.   It just seems that for hundreds of thousands of people, the barrel is not a big deal.
> 
> ...


Still waiting to hear what type of stove you are comparing to and how you determined the wood is safe.


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## bholler (Nov 16, 2017)

And now you are claiming 1/20th for some.  Come on man get serious.


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## RobbieB (Nov 16, 2017)

I like to keep the house around 68 in the winter.  Feels good with a flannel and a tee shirt or some sweats.  The only time it gets hotter than that is when I burn the stove.


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## edyit (Nov 16, 2017)

paul wheaton said:


> There is one rocket mass heater that is UL certified, and there is work being done on more.



when we installed the stove here, and when i have helped a few friends install their stoves this was top of their list, that the unit installed was UL certified, not even so much that it passed inspection, but that it was certified. I was told even if you had an uncertified unit that passed all clearances required they wanted nothing to do with it at all. I know insurance agencies can vary but that part stood out to me.


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## maple1 (Nov 16, 2017)

*I encourage everybody to keep a firm grasp on your skepticism.
*
Encouragement not required, my skepticism isn't going anywhere.

*It isn't going to be for everybody. But I think that ten years from now, half the people that burn wood will use a rocket mass heater.*

But it isn't skepticism that a RMH doesn't heat efficiently - it is skepticism over your other claims you keep bringing in about other things woodburning. Ooops there's another one. ^

*At the same time, we now have techniques to heat a home with one twentieth the wood.
*
And another. ^


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## firefighterjake (Nov 16, 2017)

I am a bit skeptical that hundreds of thousands of folks are going with rocket stoves . . . I can see these appealing to certain folks, but not this folk.


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## electrathon (Nov 17, 2017)

I absolutely love the discussion that has been going on here.  My personal belief is that the future of stoves will be some sort of mixture of what many of us now consider to be a modern stove and the rocket stove design.  I am not sure what that will be, but it will be fun as designs move forwards and evolve.


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## maple1 (Nov 17, 2017)

Yes - it is good discussion. May be something we can all agree on.


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## paul wheaton (Nov 17, 2017)

As promised, here is the new rocket mass heater that has no barrel (or barrel-like thing):


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## paul wheaton (Nov 17, 2017)

> when we installed the stove here, and when i have helped a few friends install their stoves this was top of their list, that the unit installed was UL certified, not even so much that it passed inspection, but that it was certified. I was told even if you had an uncertified unit that passed all clearances required they wanted nothing to do with it at all. I know insurance agencies can vary but that part stood out to me.



A lot of our laws are "thou shalt not innovate."   So somebody has to be bold enough to create this stuff and demonstrate it so that laws can be changed.  Fortunately, there are a few spots and situations where people can do their own thing.  And a few folks that live in places where it is illegal, but they choose to blaze that trail.

As for the one that is UL listed ....    it is all steel.  And an issue with rocket mass heaters is that they are pushing for temperatures in the core of over 1800 degrees F.   Some are even getting close to 3000 degrees F.  Steel spalls at about 1600 degress F and is liquid at 2600.   Steel cores for rocket mass heaters can work, but only for the smaller sizes - and then they need to be air cooled to keep them from getting hot enough for spalling.


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## Seasoned Oak (Nov 17, 2017)

Im sure more people would have these heaters if you could buy it at Home Depot . Or at least a Kit.


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## maple1 (Nov 17, 2017)

*As for the one that is UL listed .... it is all steel. And an issue with rocket mass heaters is that they are pushing for temperatures in the core of over 1800 degrees F. Some are even getting close to 3000 degrees F. Steel spalls at about 1600 degress F and is liquid at 2600. Steel cores for rocket mass heaters can work, but only for the smaller sizes - and then they need to be air cooled to keep them from getting hot enough for spalling.*


Why not use some refractory in strategic places? Combined with air flow in strategic places?

A lot of us on here have gasifying boilers (present company included), also commonly subject to those temps in the secondary chambers, and also commonly utilizing refractory.


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## paul wheaton (Nov 17, 2017)

> Im sure more people would have these heaters if you could buy it at Home Depot . Or at least a Kit.



I agree.   In the hopes that somebody does exactly that, DVD 3 of my 4-DVD set is all about "shippable cores".  I hope that somebody starts just such a business.  

There are some businesses out there that currently do shippable cores, but each one has something that bugs me to make it so that I feel we aren't quite "there" yet.    I think people would be willing to pay about $500 to their door for a core.   And I think that something with duraboard,  foaming cement and firebrick could have a materials cost of less than $100 per unit.







https://permies.com/t/31100/Rocket-Mass-Heater-Shippable-Core


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## paul wheaton (Nov 17, 2017)

> Why not use some refractory in strategic places? Combined with air flow in strategic places?



An excellent point.  I would like to see a variety of options.

Some people are fine with the DIY approach, but I think 9 out of 10 people would prefer a pre-made core - all the most difficult stuff is already taken care of.  

And, further, the stuff about UL listing is a big plus.


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## electrathon (Nov 17, 2017)

paul wheaton said:


> An excellent point.  I would like to see a variety of options.
> 
> Some people are fine with the DIY approach, but I think 9 out of 10 people would prefer a pre-made core - all the most difficult stuff is already taken care of.
> 
> And, further, the stuff about UL listing is a big plus.


I think most people are not willing to build their own stove.  Most will not even install a finished stove themselves.  A drop in unit would be a huge step forwards to people accepting the design.


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## paul wheaton (Nov 17, 2017)

> I think most people are not willing to build their own stove. Most will not even install a finished stove themselves. A drop in unit would be a huge step forwards to people accepting the design.



Agreed.  This is why I have pushed for shippable cores so much.


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## twd000 (Nov 17, 2017)

Really liking the barrel-less design in Donkey's video. You're on the right track with that design. Scale it up from tiny house size to 2000 SQ ft house size, standardize to use an existing chimney as the exhaust path..now you're cooking


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## bholler (Nov 17, 2017)

twd000 said:


> Really liking the barrel-less design in Donkey's video. You're on the right track with that design. Scale it up from tiny house size to 2000 SQ ft house size, standardize to use an existing chimney as the exhaust path..now you're cooking




I agree it looks really good.  But the clearances to the back wall look really really close and i didnt see any floor protection infront of it.


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## electrathon (Nov 17, 2017)

@paul wheaton :  I am noticing in many of the videos posted that thin walled galvanized pipe is used instead of heavy walled stainless.  Much of this is embedded into mortar of one form or another.  If the heat is reaching what yo have stated the lifespan on this pipe will be very short at best.  Is there any good excuse for this (like the stoves need replacing every year or so anyways) or is it just a lack of workmanship and quality standards?  It is troubling and does make it tough to believe that the builders are knowledgeable with such a simple safety detail is shunned.


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## byQ (Nov 18, 2017)

_A masonry heater builder and teacher, Eric Moshier, giving his opinion (he also taught workshops on RMH but has stopped the RMH workshops)._


Hello Satamax,

If you are going to invest 2-7+ days of your time, money and energy building a reliable, safe heating system for your home and family you are better off building a masonry heater. They have been in use for around 1,000 yrs and they work 99.9% of the time without any issues as long as they are built according to a set of plans that has been trial tested by experienced masonry heater builders and not just weekend pyro's. Any masonry heater that is properly built will out live the builder and most likely the next 5 generations. Yes, they might take a day or 2 longer to build than your typical rocket stove and cost you $500-$1,000+ dollars in materials but you are building something that will last potentially 100's of years. There is considerable testing that has been done and is still being done on masonry heaters in North America and in Europe and they have proven to be safe and work 99-100% of the time and not be temperamental like a rocket stove can be at times. Masonry Heaters are also listed in the International Residential Building Code so they can legally be built anywhere that they allow wood burning. Since they are listed in the IRBC and if built according to ASTM 1602 then the majority of all insurance companies will also cover them being built in your home. Yes there are kits and systems for building masonry heaters that will cost from ~ $1,000-$7,000 but all of these systems are guaranteed to work if built properly. As far as testing and efficiency of a masonry heater goes compared to a RMH just go onto the Lopez Labs page to see some of the work that Norbert and the rest of us have done testing masonry heaters. The Europeans have 1,000s of tests done especially on Kachelofens.
rocket mass heaters are still deemed experimental.

Not all masonry heaters are that difficult to build, yes the require some gluing together of firebricks but so do RMH's. There are simple Russian Bell Heater plans that will outperform any RMH in performance and longevity, yes they might take a day or 2 longer to build and cost you a few hundred dollars more but in the long run they will outlast and out perform and you wont have to tear it apart and rebuild it in the next 100 yrs.

Don't just build something because it is cheap and fast. You are only given so much time on this earth that you will never get back. Choose wisely.
Eric Moshier



I know the design, testing and data behind all 3 units here (J-tube, batch box, & masonry heater). *Once the data hits the table all the BS stops. It's hard to argue with hard data. *

Great conversation by the way. I am just here giving the real facts about the other side of the story (masonry heaters). I used to teach rocket stove building workshops, I just didn't like making up excuses for why they legally couldn't be built in most area's because there is no ASTM for them and they are not in the IRC so officials have issues with them. Plus they are still kinda experimental and will smoke back on you on the wrong day. A properly designed and constructed masonry heater will never smoke back on you once the draft is established. Yes, some clients might get some smoke back in the beginning of a fire IF they did not have the draft originally established. If you are having a fire 1x per day you should never have any issues with draft unless the temperature differential from outside to inside is not that great. Your not going to get a great draft if the inside temperature in 68º and your outside is 50º. Once a fire is going in a MH you should never get any smoke back if it was designed properly.
Eric


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## georgepds (Nov 18, 2017)

@byQ 

Links to test data please.


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## byQ (Nov 18, 2017)

Here are a few.

http://heatkit.com/research/2010/2010 testing summary3.pdf

http://heatkit.com/research/2007/Alex/Test report01.pdf

http://pages.uoregon.edu/hof/W09HOF/21MasonryHeater_ppr.pdf

http://mha-net.org/docs/TEST-AU1.pdf


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## byQ (Nov 18, 2017)

I'm not a mason but managed to build a large masonry heater for ~$1700. It took over a month (I had to go slow). Here is a picture of the unfinished chimney with a full firebox of grubby pine burning (I opened the doors to show the fire). I guess it works ok - no visible smoke.  I thought the fire had gone out because I couldn't see anything coming out the stack.


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## georgepds (Nov 18, 2017)

byQ said:


> Here are a few.
> 
> http://heatkit.com/research/2007/Alex/Test report01.pdf
> 
> ...





Thank you


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## twd000 (Nov 18, 2017)

Can masonry heaters be retrofit into existing construction? Part of the reason steel stoves and inserts have been widely adopted is that they FIT into the useless fireplace that almost all houses have. That's a big selling point, separate from the efficiency arguments. It's great to sketch a RMH or masonry heater design on a blank sheet of paper, but the amount of new construction every year in the US is vanishingly small. There is a huge existing housing stock of leaky homes that have to be heated.


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## twd000 (Nov 18, 2017)

...or get the exhaust temps of the RMH low enough that it could be legally vented by PVC like a propane furnace. That would open up a world of of installation options


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## georgepds (Nov 18, 2017)

twd000 said:


> ...or get the exhaust temps of the RMH low enough that it could be legally vented by PVC like a propane furnace. That would open up a world of of installation options



Hard to see how that could be done consistently. The cool emission gas stoves have controls monitoring the , quality controlled natural gas, flame 

Where is the control of a bunch of sticks, of unknown provenance and amount, burning freely in an open pit.

Might get it right once or twice , but you'll need 99.999% before you trust the exhaust of a wood burning appliance to pvc pipe


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## simple.serf (Nov 19, 2017)

My neighbor has a masonry rocket stove. His house was built in the 80's as a high efficiency test structure. Think Mother Earth News/EPA/DEC designs from the 70's and 80's. 

He doesn't use the heater anymore.  Upon some remodeling work, he found scorched timbers and other damage due to the designers not fully understanding what clearances would be needed. When he did use it, he said it was similar to anticipating your load with a gasifier and storage.


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## paul wheaton (Nov 30, 2017)

> @paul wheaton : I am noticing in many of the videos posted that thin walled galvanized pipe is used instead of heavy walled stainless. Much of this is embedded into mortar of one form or another. If the heat is reaching what yo have stated the lifespan on this pipe will be very short at best. Is there any good excuse for this (like the stoves need replacing every year or so anyways) or is it just a lack of workmanship and quality standards? It is troubling and does make it tough to believe that the builders are knowledgeable with such a simple safety detail is shunned.



About eight years ago, some risers were built with light duct and I even did it a couple of times, but, yes, it burned out, so I stopped doing it.   

I currently use that sort of thing only in spaces where the temperature will be 300 degrees F or lower.  

I currently use no metal in the core of a rocket mass heater.   Even stainless melts at 2800 - and I am shooting for temps around that.


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## paul wheaton (Nov 30, 2017)

We talked earlier about the rocket mass heater in my house.   We had videoed some stuff to put online, but the editing wasn't done yet.  And now that the editing is done ....


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## bholler (Nov 30, 2017)

simple.serf said:


> My neighbor has a masonry rocket stove. His house was built in the 80's as a high efficiency test structure. Think Mother Earth News/EPA/DEC designs from the 70's and 80's.
> 
> He doesn't use the heater anymore.  Upon some remodeling work, he found scorched timbers and other damage due to the designers not fully understanding what clearances would be needed. When he did use it, he said it was similar to anticipating your load with a gasifier and storage.


And honestly it doesnt seem like the lack of understanding of clearances has not gone away at all.  The wood in paul wheatons heater looks way to close to way to many hot parts.  And the fact that he has repeatedly ignored my questions about how those clearances were determined makes me think no testing was done at all.


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## bholler (Nov 30, 2017)

paul wheaton said:


> About eight years ago, some risers were built with light duct and I even did it a couple of times, but, yes, it burned out, so I stopped doing it.
> 
> I currently use that sort of thing only in spaces where the temperature will be 300 degrees F or lower.
> 
> I currently use no metal in the core of a rocket mass heater.   Even stainless melts at 2800 - and I am shooting for temps around that.


There are many alloys of stainless that can wothstand temps way above 2800 degrees.


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## Seasoned Oak (Nov 30, 2017)

I was under the impression there are so many BTUs in a given amount of dry wood.  No way to increase that number. About the best you could do is improve the efficiency of the burner from 75% to what ever,but only so much room there as well.  So what exactly is the magic of a RMH ,if there is any.


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## paul wheaton (Nov 30, 2017)

I feel the need to make it clear to all the readers of this thread:   I have made a life choice to not respond to posts that use Cunningham's Law.


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## bholler (Nov 30, 2017)

paul wheaton said:


> I feel the need to make it clear to all the readers of this thread:   I have made a life choice to not respond to posts that use Cunningham's Law.


So you wont address te very serious saftey questions about your designs???


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## paul wheaton (Nov 30, 2017)

> I was under the impression there are so many BTUs in a given amount of dry wood. No way to increase that number. About the best you could do is improve the efficiency of the burner from 75% to what ever,but only so much room there as well. So what exactly is the magic of a RMH ,if there is any.



First, the efficiency of the burn of a rocket mass heater averages about 93%.   And that is without the 16% adjustment that conventional wood stoves get.    Further, it is difficult to operate a rocket mass heater at low efficiency.   A lot of conventional wood stoves can easily be operated at 3% efficiency.   And if the fire goes out, but the draft is left open, all of the heated air can be pulled outside - thus operating at negative efficiency.

Next, the exhaust temp is typically about 70 to 140 degrees instead of the more conventional 350 to 600.  

There is the barrel.   When the fire goes out, the barrel acts as a thermal plug - preventing (for a while) the warm air in the house from being pulled outside.

And then there is the mass.  Thanks to the mass, we can run a short, hot fire at 6pm and the fire is out at 7:30.   We bottle things up and go to bed when it is convenient.  When we wake up, the house is still warm.  

So it isn't one thing.   It is a list of things.  And there are more things.

The bottom line is that we are focusing measurement on the woodshed rather than on the efficiency of the burn.

I put out a new video today that touches on this a little:


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## paul wheaton (Nov 30, 2017)

Somebody once expressed safety concerns that the barrel would be too hot:


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## bholler (Nov 30, 2017)

paul wheaton said:


> I feel the need to make it clear to all the readers of this thread:   I have made a life choice to not respond to posts that use Cunningham's Law.


So you cant tell us what stove the 10x claim is tested against.  You cant tell us the btu load of your house that you heated with .06 cord.  You cant defend the safety of your unit.  But you expect us to just beleive all of your hype???


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## Seasoned Oak (Nov 30, 2017)

One thing the RMH cannot do is change the laws of physics. I understand it can be very efficient,im not questioning that.  But if you need half a million BTUs to heat a large house on a cold day ,thats what you need.  The wood or twigs or whatever burned will have to have to contain those btus to startout or its not happening.  Also a 3 bedroom house could be 500Sf well insulated tight home or it could be 3000sf poorly insulated drafty one,makes world of difference.


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## bholler (Nov 30, 2017)

paul wheaton said:


> Somebody once expressed safety concerns that the barrel would be too hot:



So absolutly nothing about clearances at all just a discussion about kids and stoves.  Which btw i grew up with a stove my whole life no fence no gates and i was never burnt.  The same goes for my kids no burns either.  You seem to like answering serious questions with videos of you guys sitting around discussing things with clearly no concept of how modern wood stoves work.


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## paul wheaton (Nov 30, 2017)

bholler said:


> I am not wasting any more of my time discussing this with you.



Perhaps you don't understand the things you say?

So, the claim of heating with one tenth the wood has been proven repeatedly.   Further, I heated my montana home with 0.60 cords of wood last winter (a particularly cold winter) while maintaining an average of 69 degrees inside.  And finally, while these designs have been dramatically optimized over the last 20 years, many of the heaters from 20 years ago are still running well.  

I have hosted three international rocket mass heater innovators events and as a result I have 12 fully functioning rocket mass heaters, plus 8 that are now retired.  I feel very comfortable with the safety of all of the rocket mass heaters here.  If anybody feels less than comfortable, then I suspect that they would build their rocket mass heaters to their own comfort level.  Just because somebody else did a poor job of building a masonry stove somewhere else does not mean that these rocket mass heaters are doomed.  We intend all of our builds to last more than 20 years.  And as for safety, one of the innovators actually wrote the safety code for masonry and rocket mass heaters in portland, oregon.  

I'm not really interested in being held accountable to the standards of somebody working so hard to not understand such simple stuff.  I have better things to do.

If a person thinks they are some sort of super builder and they wish to have tests and are unwilling to use google - then it seems pretty straightforward that such a person can quickly perform their own tests.


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## bholler (Nov 30, 2017)

paul wheaton said:


> Perhaps you don't understand the things you say?
> 
> So, the claim of heating with one tenth the wood has been proven repeatedly.   Further, I heated my montana home with 0.60 cords of wood last winter (a particularly cold winter) while maintaining an average of 69 degrees inside.  And finally, while these designs have been dramatically optimized over the last 20 years, many of the heaters from 20 years ago are still running well.
> 
> ...


So in other words you have done absolutly no testing to see what the max temps on the back side of the wood is?  Do you even know what the max temp allowable is?  

And i dont know if you are implying i think i am some sort of super builder.  But i do not by anymeans.  I am at best an average mason.  But i am someone with an industrial design degree that comes with quite a bit of training in engeneering.  Who also happens to have grown up around the chimney industry and has now been doing it professionally for well over a decade.  

And if one of your innovators wrote the code that is great.  Did he do the testing to determine if your wood surrounds are safe?


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## bholler (Nov 30, 2017)

And are you still claiming that it would take 6 cords of wood to heat your house to the same average temp?  That just is not reasonable.  The only way it is even close to possible is if you are comparing your stoves to old pre epa units.  While talking about efficency numbers for modern stoves.  

And just because you guys have "proven" the 10x thing doesnt mean much when you think all of us with wood stoves wake up to cold houses and no fire.  It is hard to take your claims seriously when you clearly dont understand anything about how modern woodstoves work.


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## sutphenj (Nov 30, 2017)

Overall Interesting thread.  I've read a cord of wood is roughly 600 pieces on average (Yes lots of variables here).  Anyhow 0.6 cord would be 360 splits in this example (600 × 0.6).  Michigan winters are roughly 5 months long (Nov-Mar).  That would equate to 72 splits per month (360/5) or 2.4 splits per day (72/30).  

Assuming 600 is correct is it possible to get enough BTU's from 2.4 splits to heat a home?  Suppose the 1/10 claim math works as I easily put in roughly 20 splits per day.


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## begreen (Nov 30, 2017)

sutphenj said:


> Overall Interesting thread.  I've read a cord of wood is roughly 600 pieces on average (Yes lots of variables here).  Anyhow 0.6 cord would be 360 splits in this example (600 × 0.6).  Michigan winters are roughly 5 months long (Nov-Mar).  That would equate to 72 splits per month (360/5) or 2.4 splits per day (72/30).
> 
> Assuming 600 is correct is it possible to get enough BTU's from 2.4 splits to heat a home?  Suppose the 1/10 claim math works as I easily put in roughly 20 splits per day.


LOL I'd like to see any stove heat this place on 2.4 splits a day. I don't think you could do that in a tiny home.


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## byQ (Nov 30, 2017)

A RMH with the couch/bed built-in could burn @ 80% efficiency but deliver more heat to people via direct skin contact to the thermal mass, technically speaking. That is, the rest of the house space could be cold but the people warm if they are sitting on top of the heater.


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## bholler (Nov 30, 2017)

byQ said:


> A RMH with the couch/bed built-in could burn @ 80% efficiency but deliver more heat to people via direct skin contact to the thermal mass, technically speaking. That is, the rest of the house space could be cold but the people warm if they are sitting on top of the heater.


Yes that is absolutly true.  But who wants to live that way?  I w a nt my house warm i do t want to have to sit on a heater to be warm in my house.


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## maple1 (Dec 1, 2017)

paul wheaton said:


> So, the claim of heating with one tenth the wood has been proven repeatedly.   Further, I heated my montana home with 0.60 cords of wood last winter (a particularly cold winter) while maintaining an average of 69 degrees inside.  And finally, while these designs have been dramatically optimized over the last 20 years, many of the heaters from 20 years ago are still running well.
> 
> 
> If a person thinks they are some sort of super builder and they wish to have tests and are unwilling to use google - then it seems pretty straightforward that such a person can quickly perform their own tests.



I had to use that google to see what Cunninghams Law was. I don't have time right now to re-read all 8 pages of this thread - maybe (hopefully) later - but seems to me most of the wrong (or evasive) answering has been given by yourself.

And I don't think anything has been proven especially on the 1/10 claim.

Some of what has been said throughout is just simply not believable. As several have pointed out - there is only so much heat potential in a given amount of fuel. And 0.6 cords of wood over the course of a winter averages out to the equivalence of 14kwh/day - even assuming maximum 100% efficiency (benefit of doubt) for the wood burner. (Someone can run numbers and correct if I got that wrong - see page 3). In other words having a 1000w electric resistance heater running 14 hours a day, or a 600 watt heater for 24 hours. So, yes, it appears quite unbelievable that you can heat an entire 3 bedroom house to 69° for an entire cold Montana winter with a 600 watt electric heater. (The same as 6x100w lightbulbs. Hey, that's one for every room with maybe an extra for the biggest one  ). Who can find fault for someone being skeptical of that? Maybe, if you spent your entire day & night in very close proximity to that heater, you yourself might not get 'cold' - but there are going to be areas of the house that are going to be intolerably cold. Sorry, but the math just does not add up - and directly dealing with that math seems to be something that has not been done yet - that I have seen - by the RMH crowd. If someone experienced a 10x decrease in their wood consumption, it has come at a price of reduced warmth throughout the entire house, and a necessity of spending a great deal of time in close proximity to the heater. Plus they were doing something very wrong when they were using their previous appliance - if a house could be kept warm with 0.6 cord of wood with a 100% eff. (benefit of doubt) RMH, there is no way it would take 6 cords of wood to heat it to the same level of comfort with any modern wood stove. Even if it used 2 cords, that would mean the stove was only operating at 30% efficiency. People here have been through their own tests, every winter, winter after winter, with their own wood stoves. They are not seeing what you are claiming from wood stoves, they know what they can heat and with how much (little) wood and to what level of comfort. Hence the great skepticism (perhaps putting it mildly) to the claims - quite justified, I believe.

If language was changed to something like 'I was just as warm on 10x less wood', it would be a little more believable, especially with all the pics of people sitting and laying on their heaters. But claiming to heat an entire 3 bedroom house on 10x less wood to the same level of comfort - which is what I think I am reading - is just an 'out there' claim which I don't think is helping your cause much. As I said before, I have no doubt a RMH is a very efficient heater. And I (and many others) have seen (and experienced for going on 6 years now) first hand what burning wood at maximum burn efficiency while recovering and storing the generated heat for later use after the fire goes out can do for getting the most out of the heat potential in the wood pile. And it isn't a 10x decrease in wood consumption. But it might be if I used a big radiator in the middle of a room and spent most of my time next to it while letting most of the rest of the house go cold.


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## Patapsco Mike (Dec 1, 2017)

paul wheaton said:


> I have better things to do.



I imagine this is true for someone who is such a piece of work that there is a whole Reddit page devoted to people who think you are full of BS...

https://www.reddit.com/r/PaulWheatonWatch/top/

I'm guessing you have some good ideas and that you are super creative and smart.  But you come off like a total poophead know-it-all and that turns people against you.  You come to this forum and start talking smack about heaters with people who have been heating with wood for decades?  Come on dude.  Very, very few of us have the lack of permit requirements/enforcement that let you get away with these homebrewed heaters even if we bought what you are selling.  Dial it back, start talking with people instead of at them, or gtfo of here because we all have better things to do.


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## Seasoned Oak (Dec 1, 2017)

paul wheaton said:


> I feel the need to make it clear to all the readers of this thread:   I have made a life choice to not respond to posts that use Cunningham's Law.


The irony is, you may be the one using Cunninghams Law.  The rest of us use the law of physics which is the same for everyone.


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## Seasoned Oak (Dec 1, 2017)

Seems to me the RMH compared to EPA wood stoves is about the same as buying a condensing furnace (oil or gas) instead of a conventional furnace . Those are between 90 and 95 % efficient. They also have low flue temps and can be vented with a plastic pipe. I had  a condensing  gas furnace for a few years. Yes it was more efficient, about 10% more.  Not 100% or 1000% but 10%.  I still had heating bills of several hundred a month all winter. I removed it to switch to solid fuel heat.  Despite its  high efficiency it could not overcome my local gas companies zeal to turn one of the cheapest fuels(Nat gas) into the most expensive.


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## maple1 (Dec 1, 2017)

Patapsco Mike said:


> I imagine this is true for someone who is such a piece of work that there is a whole Reddit page devoted to people who think you are full of BS...
> 
> https://www.reddit.com/r/PaulWheatonWatch/top/
> 
> I'm guessing you have some good ideas and that you are super creative and smart.  But you come off like a total poophead know-it-all and that turns people against you.  You come to this forum and start talking smack about heaters with people who have been heating with wood for decades?  Come on dude.  Very, very few of us have the lack of permit requirements/enforcement that let you get away with these homebrewed heaters even if we bought what you are selling.  Dial it back, start talking with people instead of at them, or gtfo of here because we all have better things to do.



Yikes.


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## bholler (Dec 1, 2017)

Patapsco Mike said:


> I imagine this is true for someone who is such a piece of work that there is a whole Reddit page devoted to people who think you are full of BS...
> 
> https://www.reddit.com/r/PaulWheatonWatch/top/
> 
> I'm guessing you have some good ideas and that you are super creative and smart.  But you come off like a total poophead know-it-all and that turns people against you.  You come to this forum and start talking smack about heaters with people who have been heating with wood for decades?  Come on dude.  Very, very few of us have the lack of permit requirements/enforcement that let you get away with these homebrewed heaters even if we bought what you are selling.  Dial it back, start talking with people instead of at them, or gtfo of here because we all have better things to do.


Wow some really crazy stuff there


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## blades (Dec 1, 2017)

Most of what I have read here is people missing the main point, which regardless of heat source is storage of the btu's and those same btu's being released over an extended time.  The Key Point is mass or using material that will change when heated and revert to its former self while  radiating the stored btu's.  ( sorry there is a particular name for and I can't get it out of my lowly brain) all this stuff harks back eons it is not new. Yes, any fuel source has a finite amount of  usable btu's for conversion. It is how you store and then distribute them and containment of same that is the key. The beauty of a rocket stove is the simplicity of it in attaining an extremely low emissions without  getting all bound up in fancy piping or catalytic converters. Ya it runs against the grain of the last 20+ years but that doesn't mean it's wrong. Waking up to a cold stove- dosen't matter if the mass is still radiating the stored btu's ( shades of owb eh? ). Safety factor / clearance really no different than any other stove all depends on how the main burning assembly is constructed in the first place. look at current stoves, real basic, box in a box.  Wise way pellet stove, sawdust stoves  and a couple others are a variations on a rocket stove. Rather than regulating combustion air you regulate the amount of fuel.  ( well if set up correctly you can regulate air as well - son of a gun just described a pellet stove eh? )  As someone else mentioned the big draw back is the mass in a traditional sense but that can be circumvented by  Phase change materials. ( dang, not as bad as I thought, memory wise, just takes awhile ) have a great day all


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## maple1 (Dec 1, 2017)

blades said:


> Most of what I have read here is people missing the main point, which regardless of heat source is storage of the btu's and those same btu's being released over an extended time.  The Key Point is mass or using material that will change when heated and revert to its former self while  radiating the stored btu's.  ( sorry there is a particular name for and I can't get it out of my lowly brain) all this stuff harks back eons it is not new. Yes, any fuel source has a finite amount of  usable btu's for conversion. It is how you store and then distribute them and containment of same that is the key. The beauty of a rocket stove is the simplicity of it in attaining an extremely low emissions without  getting all bound up in fancy piping or catalytic converters. Ya it runs against the grain of the last 20+ years but that doesn't mean it's wrong. Waking up to a cold stove- dosen't matter if the mass is still radiating the stored btu's ( shades of owb eh? ). Safety factor / clearance really no different than any other stove all depends on how the main burning assembly is constructed in the first place. look at current stoves, real basic, box in a box.  Wise way pellet stove, sawdust stoves  and a couple others are a variations on a rocket stove. Rather than regulating combustion air you regulate the amount of fuel.  ( well if set up correctly you can regulate air as well - son of a gun just described a pellet stove eh? )  As someone else mentioned the big draw back is the mass in a traditional sense but that can be circumvented by  Phase change materials. ( dang, not as bad as I thought, memory wise, just takes awhile ) have a great day all



I did not miss it at all.

But the outlandish claims that were brought in unfortunately did 'the cause' more harm than good.


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## Seasoned Oak (Dec 1, 2017)

I have no doubt thatt RMH are very efficient 90%+ .I do have doubts i could get 1 million BTUs  needed to heat my 100 yr old home on a cold winter days from a few bundles of twigs.  Whatever is trying to heat this place needs to be hot ,very hot, 24/7 . May be only practical in a very low BTU load home. If Mr wheatons place only needs a few BTUs a day he could heat it with just about anything , very cheap.


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## OhioBurner© (Dec 1, 2017)

bholler said:


> So you cant tell us what stove the 10x claim is tested against.  You cant tell us the btu load of your house that you heated with .06 cord.



I wager perhaps his 10x-20x claim is based on a modern small cosmetic fireplace with the flue left open all day after a short fire. 



blades said:


> Most of what I have read here is people missing the main point, which regardless of heat source is storage of the btu's and those same btu's being released over an extended time.


This is similar to the multitude of discussions of steel vs cast iron vs soapstone although on a larger scale with much more mass. But the point of all of this is to heat our homes. Mass heaters is just one method, your thermal mass could be in the wall not the heater or maybe you don't even need much thermal mass at all if your home is well insulated and tight, and your heater/stove can regulate and burn efficiently low and slow. Thermal mass is just for heat storage, it does nothing to create heat and only needed if you can't regulate your heat otherwise. Some, like BK's for example can even do this automatically with little fuss. While my woodstock isn't automatic I have had many long periods that were 'hands off' of 24 hrs+ so I'm happy with that. And they are very clean burning. So the only real advantage I see of these RMH is potentially less wood consumption but I'm down so much less in my wood consumption compared to the prior pre-epa stove I am very satisfied with my current usage, and skeptical I could cut that by a factor of 10 and burn 1 split every day or two. With lower exhaust temps I can see this being a little more efficient, but not enough to go through the hassle of building one of these and probably having to forego my insurance and everything else (especially when I have a great working stove).


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## blades (Dec 1, 2017)

I actually toyed with the idea of getting the Wise Way pellet stove- until I found out it had been sold USS Steel - I will not do business with them again. There is still the Liberator stove ( rocket type) which they have a pellet hopper available for it now. Hopper is removable . That addition gives you a longer burn time- don't have an apx of the hours though.
The premise of the rocket stove orginally was for back country or similar areas particularly those with little resources fuel wise, not on any grids, for cooking mostly, not as a area heater per say, like our stoves. For area heating - That is where the mass comes into play.


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## jatoxico (Dec 1, 2017)

I don't think anyone is disputing what they are, what they're for or if they work. The issue is every time the questions turn to hard facts and numbers there is no legitimate info to explain the performance claims.


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## bholler (Dec 1, 2017)

jatoxico said:


> I don't think anyone is disputing what they are, what they're for or if they work. The issue is every time the questions turn to hard facts and numbers there is no legitimate info to explain the performance claims.


Exactly


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## Seasoned Oak (Dec 1, 2017)

Another thing is , most people dont want an upside down steel drum in their living room.  Now brick or stone masonry heaters are a whole different story when it come to aesthetics.  Well insulated places have very low heat requirements. I have a small house i did over very tight and well insulated. Last winter i heated it to Avg 65 degrees for most (24 days) of febuary on about $8 worth of Nat gas,for which the gas Co charged me $36.  (23ccf ) I kept the bill cuz i couldnt believe it .  The month of Jan was $15 worth of gas 46CCF.    House was empty so (gas)water heater was on but not much use.  Just me there working.


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## blades (Dec 1, 2017)

Seasoned Oak said:


> Another thing is , most people dont want an upside down steel drum in their living room.  Now brick or stone masonry heaters are a whole different story when it come to aesthetics.  Well insulated places have very low heat requirements. I have a small house i did over very tight and well insulated. Last winter i heated it to Avg 65 degrees for most (24 days) of febuary on about $8 worth of Nat gas,for which the gas Co charged me $36.  (23ccf ) I kept the bill cuz i couldnt believe it .  The month of Jan was $15 worth of gas 46CCF.    House was empty so (gas)water heater was on but not much use.  Just me there working.


 about where i was at the old place last winter - transportation charge ect were 2-2.5 times the price of the ng. combined electric and ng bill avg over winter 75/mo 2/3 of that is add on charges


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## firefighterjake (Dec 2, 2017)

I guess this sums up my opinion . . .


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## begreen (Dec 2, 2017)

If done well I would expect a rocket mass heater to approach or be similar to the performance of a good masonry heater. But there is no magic here. There are only so many BTUs in a cordwood log. If the place can be heated with a few logs a day that means that either the area heated is small, or well insulated and/or the differential between room temp and outside temp is low. One can not achieve greater than 100% efficiency burning wood, which is what some claims suggest. 90% is pretty darn respectable if that can be achieved.


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## georgepds (Dec 2, 2017)

*Why don't we all want rocket mass heaters?*

1 performance is unsubstantiated hype
2 butt ugly
3 not ul listed
4 won't get past the building inspector
5 half the posted builds say they don't work ( see #1 )
6 I don't want to learn how to build with clay and straw
7 can't insure the install
8 there are good stoves that work commercially available

But for those who like to tinker, tinker away.


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## byQ (Dec 2, 2017)

This discussion has made me realize something. Suppose you had 2 woodstoves with cats, 80% efficient, stove A and stove B. Stove A was just a normal wood stove. But stove B was constructed with metal chambers. There was a chamber in the front constructed into the form of a chair. And a chamber in the back constructed into the form of a bed. Let's say someone did the math and figured how to keep this chair and bed from burning your hide. Maybe by using more than one layer of steel/cast iron or using soapstone.

Well, people spend an average of 8 hours in bed and several more hours sitting. Because stove B has a more direct path to heating people wouldn't it use less firewood, even though both stoves are 80% efficient? I wonder how much less firewood?


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## begreen (Dec 2, 2017)

For a long time Russians built beds onto the top of their masonry fireplaces. That place was usually reserved for the grandparents. I assume this was out of kindness, but the venting on these fireplaces was often terrible, especially if you were poor, so the higher up in the room the worse the smoke. That might explain the low life expectancy of these people. 




Here is a high-end model.


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## maple1 (Dec 2, 2017)

byQ said:


> This discussion has made me realize something. Suppose you had 2 woodstoves with cats, 80% efficient, stove A and stove B. Stove A was just a normal wood stove. But stove B was constructed with metal chambers. There was a chamber in the front constructed into the form of a chair. And a chamber in the back constructed into the form of a bed. Let's say someone did the math and figured how to keep this chair and bed from burning your hide. Maybe by using more than one layer of steel/cast iron or using soapstone.
> 
> Well, people spend an average of 8 hours in bed and several more hours sitting. Because stove B has a more direct path to heating people wouldn't it use less firewood, even though both stoves are 80% efficient? I wonder how much less firewood?



Sure it would. But the house would be colder. Which is not what was being claimed elsewhere in the thread.


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## byQ (Dec 2, 2017)

The claim - 1/20th the amount of wood and the whole house is 70 F?


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## begreen (Dec 2, 2017)

Not too hard in a small strawbale house when it's 50 outside and the sun is shining.


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## maple1 (Dec 2, 2017)

byQ said:


> The claim - 1/20th the amount of wood and the whole house is 70 F?



There were a couple. One was house just as warm on 1/10 the wood. Another was 3 bedroom leaky house at 69 throughout all winter on 0.6 cord. Might have been more.


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## blades (Dec 3, 2017)

Advertising hype- got your attention didn't it , there for it worked, product might not but that is of secondary importance to the advertising agency.  Marketing 101


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## Seasoned Oak (Dec 3, 2017)

No way id be satisfied to burn wood and live in the 60s all winter. its got to be 75 to 77 or ill go back  to oil if i want to be cold all winter.  All the work of a wood stove but not the bone warming effect of a wood stove dont make sense to me.


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## georgepds (Dec 3, 2017)

Seasoned Oak said:


> No way id be satisfied to burn wood and live in the 60s all winter. its got to be 75 to 77 or ill go back  to oil if i want to be cold all winter.  All the work of a wood stove but not the bone warming effect of a wood stove dont make sense to me.




Actually, more work...you have to split the splits into tiny sticks


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## georgepds (Dec 5, 2017)

begreen said:


> For a long time Russians built _beds onto the top of their masonry fireplaces. That place was usually reserved for the grandparents_. I assume this was out of kindness, but the venting on these fireplaces was often terrible, especially if you were poor, so the higher up in the room the worse the smoke. That might explain the low life expectancy of these people.
> ......



Beats putting then on an ice floe and pushing them out into the winter sea


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## peakbagger (Dec 5, 2017)

I have seen and heard of good Russian fire place designs and bad Russian fireplace designs. Most of the time you hear about the good ones, rarely do you hear about the bad ones and most of the owners of the good design are not your typical 9 to 5 homeowner. I ran into someone on my travels who had a "good" design". He and the wife were retired and keep the unit fired as needed so i was always warm and their firewood was well seasoned and dry.  It was great except when they went away for few days or weeks. Unlike a wood stove that would be cranking out a lot of heat in an hour or less when they got home, it took a real long time like overnight for the russian fireplace to be putting out heat. I know of a couple bad designs where the pressure drop for the internal passages exceeded the available draft from the chimney  Net result getting a fire going was very difficult. In one case I heard of is the mason came in with a jackhammer and went in through a clean out port and jack hammered a bypass between the firebox flue and the main stack to get it to run. It would run once they took out all extra resistance but it was an awfully expensive exercise. I have heard of at least two others over the years that got jack hammered out.  

Reminds me of the oil fired electric radiator scam. The selling point was the radiator gave off heat after the power was off. The trade off was it took longer to warm up. There were all sorts of claims as they being more efficient but given that electric heat is effectively 100% efficient, kind of hard to get much more, unlike the fabled amplifiers from Spinal Tap, efficiency doesnt go to 11


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## begreen (Dec 5, 2017)

The Russian bed fireplaces are different from the more modern Russian fireplaces. We have several in our local area due to Wesleyans living here a while back. They had some master masons amongst them and the fireplaces they built are excellent heaters. I have been around a few of them, one at all times of the winter. Built right, they work well and are quite easy to run.


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## maple1 (Dec 5, 2017)

That could be pretty risky business for a home owner, with either a Russion/masonry heater, or a rocket mass heater. If it doesn't get done right and work right it's pretty hard to do over.


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## Seasoned Oak (Dec 5, 2017)

peakbagger said:


> Reminds me of the oil fired electric radiator scam. The selling point was the radiator gave off heat after the power was off. The trade off was it took longer to warm up. There were all sorts of claims as they being more efficient but given that electric heat is effectively 100% efficient, kind of hard to get much more.


Still dont know what the selling point of the Edenpure is . $300 for a 1500 watt plug in electric heater. Lots of knock offs for under $200 still highway robbery.
The only unsung hero in small electric heaters is radiant. I have a  500 watt ceiling radiant ($39) but need to be installed, that warms a large bathroom with no other heat source, comfortably all winter. Its only in use when occupied.


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## georgepds (Dec 5, 2017)

peakbagger said:


> .... efficiency doesnt go to 11




Except ,of course, for heat pumps


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## georgepds (Dec 5, 2017)

Seasoned Oak said:


> Still dont know what the selling point of the Edenpure is . $300 for a 1500 watt plug in electric heater. Lots of knock offs for under $200 still highway robbery.
> The only unsung hero in small electric heaters is radiant. I have a  $500 watt ceiling radiant ($39) but need to be installed, that warms a large bathroom with no other heat source, comfortably all winter. Its only in use when occupied.



Can you identify the model?

I'm looking for one


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## Seasoned Oak (Dec 6, 2017)

georgepds said:


> Can you identify the model?
> 
> I'm looking for one


The radiant heat bathroom ceiling is sold under Nutone and also Broan. 
https://www.homedepot.com/p/Broan-500-Watt-2-Bulb-Ceiling-Infrared-Heater-163/202905928


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## Seasoned Oak (Dec 6, 2017)

byQ said:


> Well, people spend an average of 8 hours in bed and several more hours sitting. Because stove B has a more direct path to heating people wouldn't it use less firewood, even though both stoves are 80% efficient? I wonder how much less firewood?


If it were just about warming you while you sleep ,they have electric blankets and electric mattress pads that use a few pennies a day for that. You would still wake up to a cold house ,in which you do not want to have to be limited to sitting in your warm chair all day in order to keep warm.  What your trying to achieve can best be done with higher levels of insulation. A smaller home very tight and well insulated has a very small heat load. sometimes only 10 or 15K Btus an hour. Solar exposure can help a lot as well.  In such a place just the heat from people and appliances,cooking ect, at times are enough.  Iv done it so i know it works.


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## Dantheman300z (Dec 6, 2017)

maple1 said:


> Sure it would. But the house would be colder. Which is not what was being claimed elsewhere in the thread.



Maple1: If you notice one of Paul's other posts it is a video of the 87% electric bill cut/ or heating bill. Pauls house in other rooms will be colder because he uses lights and lamps as heat, has a heated keyboard and other devices. So his main room will be 69 degrees but he learns to cope with other room colder.

I like Paul, I read his forum and this one, only two things I do much in the Internet. He does have some very good ideas.


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## Seasoned Oak (Dec 6, 2017)

Dantheman300z said:


> Pauls house in other rooms will be colder because he uses lights and lamps as heat, has a heated keyboard and other devices. So his main room will be 69 degrees but he learns to cope with other room colder.


That provides more clarity, He is not heating his house to 69 Deg.  with just .6 cords of wood. He is heating 1 room to 69 with .6 cords of wood and the rest of the house with electric to less than 69.   A small cat stove might be able to turn in close to those numbers, although would have to be a very small stove to heat only 1 room to 69 or less.


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## peakbagger (Dec 6, 2017)

Dick Hill had a combination masonry heater/wood stove he was experimenting with in his final years. I expect it would be very similar in heating efficiency to a rocket mass heater. http://www.hotandcold.tv/masonry_stove.html. His innovation of using a stainless steel screen in place of an actual catalyst was ingenious and cheap. I think his building was a much older home that would be far less energy efficient than a newer one so his total heating demand would be higher. He was also quite active but elderly at that point and expect that he probably maintained a higher heating temperature than 69 degrees.  That's the problem with trying to compare fuel use and efficiency for a cyclical heating source, unless two identical spaces are built with the same solar exposure, climate conditions with equivalent thermal mass and then maintained at a set temperature for a long period with different heating sources any comparisons are apples to oranges. Good for bragging but not so good for real data points.


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## Seasoned Oak (Dec 6, 2017)

This kind of heating is being done every day with a gassifier boilers and storage. The hot water storage taking the place of  tons of masonry. Many similarities, including clean burns, high combustion temps and not having to  fire it every day on milder winter days.  Although no one is claiming extremely low wood use with these systems.


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## maple1 (Dec 6, 2017)

Seasoned Oak said:


> This kind of heating is being done every day with a gassifier boilers and storage. The hot water storage taking the place of  tons of masonry. Many similarities, including clean burns, high combustion temps and not having to  fire it every day on milder winter days.  Although no one is claiming extremely low wood use with these systems.



Yes, that's another point. I replaced a very inefficient wood/oil combo boiler with a gasser + storage. The old one was about as inefficient as you could get, boiler wise. Everything else remained the same. So I sort of did the same thing as would be done by replacing an inefficient wood stove with a very efficient burn+storage RMH. Sure, I saw consumption drop, but nothing like the touted 1/10 claim. I think I cut my consumption by maybe 25-30%, but also saw a somewhat warmer house, I think. So realistically speaking, a 1/2 reduction claim may have been believable assuming a very inefficient stove as baseline. But 5x that much, uh, no - everything else is definitely not remaining equal.


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## Seasoned Oak (Dec 7, 2017)

The biggest factor here is the RMH is heating only 1  Room to a not so warm 69 or lower . This is not a big deal.  Various electric heaters in the other rooms which are colder.  May as well make it total electric and change out the stylish barrel in the living room for a mini split. Skip the work gathering twigs altogether.


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## Seasoned Oak (Dec 7, 2017)

maple1 said:


> So realistically speaking, a 1/2 reduction claim may have been believable assuming a very inefficient stove as baseline. But 5x that much, uh, no - everything else is definitely not remaining equal.


The difference is ,your house is warm.


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## Squisher (Dec 7, 2017)

These sorts of temps being discussed are part of why I don't really see something like this catching on. For me a big part of the picture of wood heat is having a splendidly warm house. Were the whole thing becomes warm 75 in the far reaches of the home. 

I would hate to heat with wood and be chilly still. That would be an awkward conversation with the missus too. 

Wife, "we need a fire!"
Me, "it's already going" , or "we've already used our stick of wood for the day."

I don't foresee the above conversation ending well.


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## RobbieB (Dec 7, 2017)

I like to wear long sleeve flannel shirts with a tee underneath.  72 is too warm for me, I like it around 68.

With a fire going it gets to 75-77 in a couple of hours and then the clothes need to come off.  Which is why I have a stove, romance and ambiance -


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## edyit (Dec 7, 2017)

if i'm going to keep it at any temp under 76 i might as well just run the oil burner. the wife being warm was one the biggest deciding factors in getting wood heat. we both grew up with it, when we moved in together she wasn't as keen on the idea of sitting in a 62F house in a sweater because fuel oil isn't exactly cheap in the adirondacks (or anywhere for that matter) so in came the stove and now the average temp is around 76-78 and i don't have to hear i'm cold or worry about the power going out


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## georgepds (Dec 7, 2017)

RobbieB said:


> I like to wear long sleeve flannel shirts with a tee underneath.  72 is too warm for me, I like it around 68.
> 
> With a fire going it gets to 75-77 in a couple of hours and then the clothes need to come off.  Which is why I have a stove, romance and ambiance -





It's sort of like that in my house, but ,really, the view of me in my skivies just doesn't kindle romance anymore.....


Maybe I need a RMH


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## OhioBurner© (Dec 7, 2017)

Yeah temperature is entirely personal. I shoot for upper 60's. Lately I've been reluctant to fire up both my stoves (usually needed below freezing) and since the temps have dropped the last couple days my house is down to about 60 throughout with the stove room being 68. Mid 70's I'd be wearing boxers. But then again most of the winter I am still barefoot outside. Cold doesn't bother me as much as several thousand dollar propane bill, but I do like at least 60's.


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## peakbagger (Dec 7, 2017)

I generally could care less about the actual room temp as long as there is good radiant heat from the stove.

I hang out in front of campfires in the winter on occasion.  It may be below zero but if I am standing in front of the fire I am plenty warm from the radiant heat. 

I do miss the radiant heat aspect with my wood boiler which is in the basement. Heat from the boiler and the flue actually heat my insulated living room floor but the rest of the house is baseboard. On occasion when I get home after a few days to a cool house, I fire off the boiler and hang out in front of it until the house warms up. Same with my minisplit I find that I need to run a higher temp as I dont have any radiant heat.


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## Seasoned Oak (Dec 7, 2017)

I d like to hear for others using a RMH  that actually keep their entire house warm with just the wood. To get a more accurate comparison to a conventional wood stove.   I do think there is more efficiencies that can be had from a wood stove but perhaps its a diminishing return thing as far as complication and expense of mfg. Just what would it take to go from 70 % to 90+ % with a wood stove ,I feel if it were that simple it would have already been widely done.


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## FarmerDan (Feb 16, 2018)

Caught up with this whole thread, and started spelunking around the internet. In general, I think it's a pretty cool DIY-idea. It simultaneously makes sense that it's completely un-insurable AND it's a shame that this cool, low-tech heating solution has a lot of burdens in front of it. 

One thing that's been a sticking point in all the articles/videos supporting the wonders of the RMH is the low, low wood use and how things appear to defy physics. Wood does have a maximum burning temperature (~1,000dF) and btu content, correct? I finally found a video that jives with my understanding of how wood heating, in general, words. These folks appear to give an good, open review of the RMH, they live in a pretty small home with an open floor plan and estimate that in the Boise, ID area they would use 2 cords over a 96 day period. Boise doesn't appear to have super aggressive winters. This estimate of wood use feels like a more reasonable amount of wood. What do you think? Of course, like we've discussed, hard comparisons are difficult to come by. 

From my poking-around research, 

with the unique nature of each RMH build, comparisons appear to be difficult.
mass appears to be the biggest key of these stoves stoves in particular. the rocket part, I'm not convinced
masonry stoves are pretty awesome. most homes can't handle them without major renovations (like my drafty farm house built in the 1880s)
mass (extracting maximum heat from combustion into living area), home insulation (keeping that heat inside), and square footage (less space, less btus required) of the home appear to be the biggest factors in reducing wood use
The video shows that the sitting areas surrounding the stove can get uncomfortably hot when firing. They hope to finish the exterior of the stove to make it look more aesthetically appealing. They disclose that it's a different type of wood-burning lifestyle. But, this style of wood burning appeals to their lifestyle. But overall appears to be a unique and affordable way of designing a wood-burning appliance for the home, if you're down to clown with these accompanying quirks.  

As discussed here, insurance, permits, appearance and DIY-nature will be the huge barrier in before gaining a _mass_ive (hyuk hyuk) RMH following. 

Thanks for the discussion, folks! If anyone sees one in action in southern Wisco, lemme know.


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## jetsam (Feb 16, 2018)

There's a lot discussion but no actual people who heat with rocket stoves/mass heaters as far as I can tell. 

"I want to heat my house with a rocket stove", yes. 

"I currently heat my house with a rocket stove", no.


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## bholler (Feb 16, 2018)

jetsam said:


> There's a lot discussion but no actual people who heat with rocket stoves/mass heaters as far as I can tell.
> 
> "I want to heat my house with a rocket stove", yes.
> 
> "I currently heat my house with a rocket stove", no.


Well there is paul wheaton.  He heats his doublewide (that would take 6 cords with a regular stove lol) on .6 cords.  Unfortunately he is so full of crap on everything else there is no reason to beleive that.


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## begreen (Feb 16, 2018)

For all its benefit of even heat mostly due to mass, it doesn't seem to be worth the hassle. We have a few nicely built Russian Fireplaces in our area. They do a great job of even heating, but not much more as compared to a good woodstove with a lot of mass. They need to be fed twice a day - check, so does our stove. Cleaned out once a year - point to our stove which is an easier clean. Fire view - um no, not usually, though it's possible to design in. Ease of installation - many points to the wood stove over the masonry stove. Clean burn - about a wash if the masonry fireplace is well made. Fuel consumption - about the same, btus are btus, though some dispute this. Even heating - point to the masonry stove, but a stove with a lot of thermal mass will provide similar experience.


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## Seasoned Oak (Feb 18, 2018)

Its almost impossible to compare one house to another. Just on the basis of air infiltration and insulation level alone. As someone who has been a real estate developer and owner of dozens of homes for 35 years each one is vastly different.  Even well insulated homes that were not done correctly can skew the results. I went from using 161 Million BTUs a season to 69 Million  in my own 3000SF old drafty 100+ yr old home. in the span of 15 yrs. The big 3 factors were adding some passive solar, plugging up air leakage and adding cellulose insulation and removing fiberglass insulation. Some of the reduction may have come from milder winters, but this winter which was brutal so far I'm still on track for no more than 70 million. I keep this castle at about 77-78 degree avg.


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## Seasoned Oak (Feb 18, 2018)

bholler said:


> Well there is paul wheaton.  He heats his doublewide (that would take 6 cords with a regular stove lol) on .6 cords.  Unfortunately he is so full of crap on everything else there is no reason to beleive that.


And if you read between the lines,he was only partially heating ONE room to the 60s. The other rooms with a combination of small electric heaters.


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## illini81 (Feb 18, 2018)

begreen said:


> For all its benefit of even heat mostly due to mass, it doesn't seem to be worth the hassle. We have a few nicely built Russian Fireplaces in our area. They do a great job of even heating, but not much more as compared to a good woodstove with a lot of mass. They need to be fed twice a day - check, so does our stove. Cleaned out once a year - point to our stove which is an easier clean. Fire view - um no, not usually, though it's possible to design in. Ease of installation - many points to the wood stove over the masonry stove. Clean burn - about a wash if the masonry fireplace is well made. Fuel consumption - about the same, btus are btus, though some dispute this. Even heating - point to the masonry stove, but a stove with a lot of thermal mass will provide similar experience.



Another factor is the effect on the value of your home.  A relatively small number of people are interested in heating their homes with wood.  A practically infinitesimal number of people are going to be interested in heating their house with a rocket mass heater.

Thankfully, wood stoves can be removed without too much trouble, but good luck "undoing" a rocket mass heater.  In general, my guess is that if you put one in, you're home value goes into the toilet.  You may love it, but good luck finding someone to buy your house.


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## Seasoned Oak (Mar 27, 2018)

Has anyone tried to place mass in the form of stone ,sand or any type of heat absorbing material around a regular wood stove in order to even out the normal heat swings of the typical burn cycle of a wood stove. Possibly like a fireplace surround. I may try this in a house im rehabbing to possibly move into. Im wondering if its worth the effort.


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## begreen (Mar 27, 2018)

Essentially this is what the cast iron jacket does on steel stoves like the Jotul F45, 50, 55, Alderleas, etc.. Yes there are past threads on this topic, simplest I recall was someone building a cement block surround. Not sure how that worked out over the long term. Definitely not a nice look for the living room.


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## Seasoned Oak (Mar 27, 2018)

begreen said:


> Not sure how that worked out over the long term. Definitely not a nice look for the living room.


With mountain stone over it  would look good. I was thinking cement block filled with sand and faced with stacked stone to make a large fireplace like structure that surrounds the stove but is not to close to the stove so i can access behind it. The underside above would taper up toward the front to keep air circulation moving. House is a very open floor plan.


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## Nateums (Mar 28, 2018)

Wood combustion also produces CO, that alone is enough reason to not have a horizontal draft like in these things. You combine that with the claim that the flu temps are very low, you're going to have dangerously little draft.

The 'mass' part is equally ridiculous. There is likely more mass in the drywall in your house than from those mud benches. 10 yards of concrete (a truck load full to the gills) would give you an 800 sq ft 4" thick slab that most houses have in their basement - again, way way way more than the stucco stove has. Thermal mass/storage is overrated.

Put the pencil to the paper and do the math. None of these 'experts' that 'designed' this heater are professional engineers or are in any way qualified to tell you these heaters are safe. I would love to see an actual expert, by the legal definition, opine on the specifics of how dangerous this is.

At the risk of being even more confrontational I will also say that my impression of Paul Wheaton is that he is running a cult, in the literal sense, out in Montana.


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## maple1 (Mar 28, 2018)

*Thermal mass/storage is overrated.*

That part I don't think I would agree with, at least in the generalized sense. Storage and its benefits have been a game changer for me, coupled to our boiler.


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## Nateums (Mar 28, 2018)

In the generalized sense, take the total mass within your thermal envelop and look what percentage goes to the rocket mass heater, or the soapstone on your stove.


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## maple1 (Mar 28, 2018)

Yes, but all that 'other' thermal mass can't store the heat as fast as my boiler can make it. Which defeats the purpose of the mass. Whereas the 700 gallons of water can ably do that, and also send it exactly where it needs to in a very controlled fashion.

We might be talking apples & oranges by having a boiler & storage in this conversation/thread.


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## Nateums (Mar 28, 2018)

My main reason for responding is that there is a lot of misinformation out there about how dangerous these contraptions are.

The wikipedia article itself just references and links to sales materials. Paul Wheaton just keeps linking to his DVD in this thread. This is a blatant scam.

Adults should know better, but I shutter to think of these being installed in homes with kids in them.


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## maple1 (Mar 28, 2018)

Nateums said:


> My main reason for responding is that there is a lot of misinformation out there about how dangerous these contraptions are.
> 
> The wikipedia article itself just references and links to sales materials. Paul Wheaton just keeps linking to his DVD in this thread. This is a blatant scam.
> 
> Adults should know better, but I shutter to think of these being installed in homes with kids in them.



I don't think I see anything there to disagree with.


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## bholler (Mar 28, 2018)

Nateums said:


> My main reason for responding is that there is a lot of misinformation out there about how dangerous these contraptions are.
> 
> The wikipedia article itself just references and links to sales materials. Paul Wheaton just keeps linking to his DVD in this thread. This is a blatant scam.
> 
> Adults should know better, but I shutter to think of these being installed in homes with kids in them.


The idea of thermal storage is not a bad one at all.  It has been used very effectivly in europe with their masonry heaters for a long time.  And properly designed i see no reson a rmh could not do a good job heating a house safely if it was designed right.  That being said much of the designs i see from wheaton and his buddies are unsafe without question.


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## bholler (Mar 28, 2018)

And i would have to say you are not far off with the cult statement either


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## Seasoned Oak (Mar 28, 2018)

maple1 said:


> *Thermal mass/storage is overrated.*
> 
> That part I don't think I would agree with, at least in the generalized sense. Storage and its benefits have been a game changer for me, coupled to our boiler.


The mass in a large house is certainly a factor. Even my partially insulated 3 story double home holds a certain amount of latent heat within the walls,floors,furnishings,large aquariums ect. Temps fall very slowly in a no heat situation,so much so that i sometime run one load of wood a day in winter 12 hr heat,12 hr no heat. Start at 10Pm,Stove out by 10 to 12 noon next day ,house stays warm enough on sunny winter days so can go until 10PM again before firing up the stove. Not more than about an 5-8 degree swing in temps in 24 hr period.


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## maple1 (Mar 28, 2018)

Seasoned Oak said:


> The mass in a large house is certainly a factor. Even my partially insulated 3 story double home holds a certain amount of latent heat within the walls,floors,furnishings,large aquariums ect. Temps fall very slowly in a no heat situation,so much so that i sometime run one load of wood a day in winter 12 hr heat,12 hr no heat. Start at 10Pm,Stove out by 10 to 12 noon next day ,house stays warm enough on sunny winter days so can go until 10PM again before firing up the stove. Not more than about an 5-8 degree swing in temps in 24 hr period.



Yes, it is. It is likely even more noticeable going the other way - in how long it takes to recover, after everything has cooled off. Takes quite a while to warm up a house and everything in it - all that 'stuff' needs to soak up the heat again.


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## Seasoned Oak (Mar 28, 2018)

Nateums said:


> My main reason for responding is that there is a lot of misinformation out there about how dangerous these contraptions are.
> .


What im contemplating is using my regular EPA stove i have now, but building same mass around it ,like about a ton or 2 of mountain stone as fireplace type structure around the stove(but leaving sufficient air space around the stove) to absorb some of the excess heat at startup and give some back after the wood has burned to coals. Im wondering if this is worth the effort. Sort of the Mass part, of the equation but not the rocket part. Im also doing this because i like the look of a large fireplace.


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## Seasoned Oak (Mar 28, 2018)

maple1 said:


> Yes, it is. It is likely even more noticeable going the other way - in how long it takes to recover, after everything has cooled off. Takes quite a while to warm up a house and everything in it - all that 'stuff' needs to soak up the heat again.


Works out well because the big harman makes TOO much heat and actually overheats the finished first floor a bit but im not spending time there overnight.


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## bholler (Mar 28, 2018)

Seasoned Oak said:


> What im contemplating is using my regular EPA stove i have now, but building same mass around it ,like about a ton or 2 of mountain stone as fireplace type structure around the stove(but leaving sufficient air space around the stove) to absorb some of the excess heat at startup and give some back after the wood has burned to coals. Im wondering if this is worth the effort. Sort of the Mass part, of the equation but not the rocket part.


I honestly dont know if it would be worth the effort.


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## OhioBurner© (Apr 3, 2018)

FarmerDan said:


> As discussed here, insurance, permits, appearance and DIY-nature will be the huge barrier in before gaining a _mass_ive (hyuk hyuk) RMH following.



I am guessing this style of heater is going to be more for the folks that don't utilize insurance, need any permits, and would rather DIY stuff inexpensively rather than pay high dollar for factory made products. And it seems they can be made to look very nice, I like the granite top used in the one video, just the barrel that sticks out a bit. But stoves used to be made out of barrels... something nicer of course is possible. Of course beauty is in the eye of the beholder, as even on these forums folks argue about stove looks and how but ugly this or that one is.



illini81 said:


> Another factor is the effect on the value of your home.  A relatively small number of people are interested in heating their homes with wood.  A practically infinitesimal number of people are going to be interested in heating their house with a rocket mass heater.
> 
> Thankfully, wood stoves can be removed without too much trouble, but good luck "undoing" a rocket mass heater.  In general, my guess is that if you put one in, you're home value goes into the toilet.  You may love it, but good luck finding someone to buy your house.



Have you looked into the folks that are experimenting with these? I don't think home resale value is a big item for them. Paul Wheaton and his associates seem to be more of the homesteader types. I mean they use outhouses... resale value I am sure isn't weighing in. It's a different culture. Even still it's probably no harder to remove (maybe much easier) than my gigantic brick fireplace. Just that a wasteful gigantic brick fireplace is more acceptable to the masses. But yes as an answer to why they won't appeal to the general wood burning population I am sure many would be concerned of resale value.



maple1 said:


> *Thermal mass/storage is overrated.*
> 
> That part I don't think I would agree with, at least in the generalized sense. Storage and its benefits have been a game changer for me, coupled to our boiler.


You can't just make a blanket assumption that it's overrated or not...Thermal mass/storage is one characteristic that may or may not be useful depending on the circumstance. A well insulated home with conventional furnace works fine with little thermal mass, the controls regulate the temperature to keep it relatively even. Something like a passive solar home with thermal mass utilizes the suns heat to warm the thermal mass which is needed to store the thermal energy for the night when there is no sun. Some woodstoves even regulate just fine like a BK with thermostat control. A RMH pretty much requires a large thermal mass by what I've read, as it uses the method of extremely fast & hot fire to fully utilize all the combustibles in the wood, as opposed to say a CAT stove that burns low and smolders but uses a combustor to extract the heat from the fuel. This rapid release of heat benefits from thermal mass to smooth out the release of heat into the home. At least that is the basic theory.

I may have missed it since I haven't read all the pages or done a lot of research on these, but how does one clean the flu? Some of these designs like the main one talked about earlier using the horizontal flue with a U bend and double layer all sealed in the thermal mass? Maybe it does indeed burn so clean it's not an issue but what about getting the fire established and all the smoke and soot initially? Or does the intense fire self clean all that back out every time??


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## Seasoned Oak (Apr 3, 2018)

bholler said:


> I honestly dont know if it would be worth the effort.


I was wondering about that. I guess there is a way to calculate the heat storage capacity of a given weight of material to find out. LIke is said i love the look of a fireplace but not the efficiency of it. This way i get the look and the long burns and also dont suffer from insert heat trap.


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