Why dont we all want rocket mass heaters?

[maple1]

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?

 

[georgepds]

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

 

[maple1]

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.

 

[paul wheaton]

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.

 

[paul wheaton]

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.

 

[paul wheaton]

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.

 

[paul wheaton]

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.

 

[paul wheaton]

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.

 

[paul wheaton]

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.

 

[electrathon]

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.

 

[paul wheaton]

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:

 

[bholler]

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.




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




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.




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.

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.

 

[georgepds]

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

 

[twd000]

Matt Walker is another rocket mass heater designer that I have a lot of respect for.
(broken link removed to 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.

 

[maple1]

Catch up? They're already 10 times better.

 

[paul wheaton]

Matt Walker is another rocket mass heater designer that I have a lot of respect for.
(broken link removed to 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.

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.

 

[bholler]

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.

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

 

[bholler]

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.

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.

 

[RobbieB]

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.

 

[bholler]

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.

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

 

[georgepds]

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

 

[Squisher]

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?

 

[bholler]

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.

 

[Squisher]

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.

 

[twd000]

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