Thoughts on rocket mass heaters

[St. Coemgen]

b). If it were possible to construct a burn chamber for wood that resulted in 100% complete combustion (only H2O and CO2 byproducts ) at any cost less than 5000$ It would have been done. So Creosote will form somewhere if flue gas is below 200 degrees.

I agree with your concerns. And the costs.

A properly built masonry heater** can burn mostly to complete combustion. But they are not cheap. I was quoted $10,000 per stove (in Hungary where labor costs were quite low) and needed two of them to heat our space (I actually had professional masonry heater builders come in and give a bid). One said, at risk of loosing a contract, he would not recommend mass heaters for our house. And when a pro is willing to loose money to be honest, one should maybe listen to them.

My Hungarian wife was disappointed. She really wanted a traditional stove. So I put a crow bar in my wallet and bought a high quality commercial stove with tile sides (also was not cheap) and she is quite happy with that one. And it is darn good heater for the house. So I am also happy with it. Crisis avoided.


** I am not sure all these DIY heaters are "properly" built for ideal efficiency. It may depend.

 

[Hobbit Man]

I take this perspective.

a). 1 pound of wood only has so much heat.
b). If it were possible to construct a burn chamber for wood that resulted in 100% complete combustion (only H2O and CO2 byproducts ) at any cost less than 5000$ It would have been done. So Creosote will form somewhere if flue gas is below 200 degrees.
c) adequate maintenance inspection and cleaning for some RMHs seems difficult to nearly impossible.
d) would any licensed engineer sign off on any design or install?
e). Design and concept has had plenty of time to be come more widely accepted and utilized than it. That makes me cautious and or skeptical.
f) show me how how it meets code to get insurance

Those points aside, 1500$ plus venting buys you a good UL listed epa certified stove. I get that the cost might be significant to some. Do it safe and do it right the first time. If I were to have a chimney fire id need to replace my liner. Easy job. 90 minutes tops. What gets replaced/repaired and how on a RMH? Yes I’m out 600-1000$ In parts. won’t even make my insurance deductible. But because I chose a UL listed system and followed code as long as flaming creo chunks didn’t light my roof on fire I would be fine.

So how would in do it? I don’t know of a way that would give the safety margin I need for me and my family.

You bring up so good points. i will admit this is my very first attempt at building a RMH, and i guess i just hit the right ratios , cause this thing ROCKETS ! This is why the clearances are not there, did not expect this "thing" to work that good (or hot).
So since i am here to learn, here are the questions ;

First, they claim these stoves burn HOT and yes, mine does do that....
They claim it burns EVERYTHING, and since it only exhausts co2 and steam, its a very clean burning stove.

Question 1. can you still get Cresote in your ducting from co2 and steam ? and where does it come from if the stove is burning so hot ?

Second, part of the sales pitch states that if there is a chimney fire, the mass will absorb the heat ( since the first 20 feet or so of chimney is actually in the mass ) question is, if you clean the outer portion of the chimney ( regular sweeping) would this not be the case ?

Thank you for an idea. I had to go to 18 different architects to get my house plans drawn up, and the one who finally did draw them up has an engineer on speed dial - for just those types of funky projects...
I will have to contact him. if he will sign off on a rocket mass heater, it should be good enough for the insurance.

 

[bholler]

You bring up so good points. i will admit this is my very first attempt at building a RMH, and i guess i just hit the right ratios , cause this thing ROCKETS ! This is why the clearances are not there, did not expect this "thing" to work that good (or hot).
So since i am here to learn, here are the questions ;

First, they claim these stoves burn HOT and yes, mine does do that....
They claim it burns EVERYTHING, and since it only exhausts co2 and steam, its a very clean burning stove.

Question 1. can you still get Cresote in your ducting from co2 and steam ? and where does it come from if the stove is burning so hot ?

Second, part of the sales pitch states that if there is a chimney fire, the mass will absorb the heat ( since the first 20 feet or so of chimney is actually in the mass ) question is, if you clean the outer portion of the chimney ( regular sweeping) would this not be the case ?

Thank you for an idea. I had to go to 18 different architects to get my house plans drawn up, and the one who finally did draw them up has an engineer on speed dial - for just those types of funky projects...
I will have to contact him. if he will sign off on a rocket mass heater, it should be good enough for the insurance.

View attachment 301501

None of us are questioning if they burn hot. We know they do.

None of us are questioning that they burn very clean. We know they do.

What is in question is the claims of saving massive amounts of wood. The only actual reputable testing we have is from the liberator hooked to a mass and yes it is more efficient. By a couple percentage points. That simply isn't going to add up to much of any wood savings.

And goodluck finding an engineer to sign off on your contraption putting his reputation and business at risk by doing so.

 

[begreen]

Even if the RMH was 100% efficient (it's not) a pound of wood only has so many BTUs. A few pounds of wood will not heat our house on a cold day. There simply are not enough calories in that amount of wood to offset the heat loss of the house.

 

[EbS-P]

None of us are questioning if they burn hot. We know they do.

None of us are questioning that they burn very clean. We know they do.

What is in question is the claims of saving massive amounts of wood. The only actual reputable testing we have is from the liberator hooked to a mass and yes it is more efficient. By a couple percentage points. That simply isn't going to add up to much of any wood savings.

And goodluck finding an engineer to sign off on your contraption putting his reputation and business at risk by doing so.

Even moden EPA stove with a catalyst can create creosote. My point was that while they RMH burn clean (how clean though) those extremely high temps will eventually deteriorate the firebox. I don’t think enough R and D has been done (and I could be wrong) to prove the long term safety to me in my house with my family.

And yes is should not produce creosote but every cold start will have smoke and a cold flu that equals creosote somewhere. Does it get burnt off or left to accumulate?

If I were to want to build one and get it insured it would be built on a slab. I would do minimum 36” clearance to combustibles for anything I constructed, Hooking it to a code compliant chimney system. And install a mini split for my “primary “ HVAC. Now you have a compliant but unlisted heater which code really won’t allow but maybe an inspector sees it more as art or a furnishing. Now I think to the insurance company I would be up front about an unlisted stove and provide All the relevant documentation to it meeting code for an unlisted appliance. They may not want to cover you. If paying cash you could spend time shopping around to maybe find one that will but if a bank has a note on the property and you are uninsured well that’s bad news.

So to summarize I don’t get all the effort and hassle to go the RMH route when for a couple thousand dollars you can meet code get insured and save lots of time. RMH are Not saving a significant or any wood usage. Well build RMH could be safe we don’t know. What is the well build standard? I do get the allure of “look I did all myself” but you have an architect so you value experts and their knowledge.

 

[john26]

If I wanted a mass heater I would go this route it is UL listed and should be easily insurable if installed per code and owners manual. No its not a rocket mass heater but a mass heater with a 2-3 hour burn time depending on size. In compared to to the rocket mass heater with the steel barrel it has a viewing window that would be important to me. If I didn't want a fire view I would buy a wood boiler or furnace. However look the price and the small amount of rated heating square footage. I could not find anything in the manual or website about actual efficiency ratings or emission numbers as far as producing heat not an actual defined amount of time.
"Soapstone fireplaces burn wood exceptionally clean and at a high rate of efficiency.
This fireplace will spread heat slowly and evenly throughout your home for several hours after it burns out."

 

[St. Coemgen]

This fireplace will spread heat slowly and evenly throughout your home for several hours after it burns out."

Yes, mass heaters release heat slowly over time. But "evenly throughout your home" is questionable.

Again, we are talking about some basic concept of physics. Heat does not passively move "equally" in the time frame needed to heat a real world house. For example, walls in the way will affect heat transfer. So unless you live in a Yurt which is one big room, you will not get "even" heat distribution. Not even close. Anyone here with a wood heater in one room will tell you the rooms in the back of house will not be as warm.

Reality sucks, but hype is worse.

Reality can be corrected for. But hype invokes magical thinking, and if you fall for that you may need magic to fix things later.....

Hope this helps.

 

[St. Coemgen]

They claim it burns EVERYTHING, and since it only exhausts co2 and steam, its a very clean burning stove.

Today, online, anyone can "claim" anything. And exhaust is not the same thing as what is happening along that entire pipeline from combustion chamber to exhaust outlet.

What I can say, is typically mass heaters have a life span. And need to be torn down and rebuilt to some extent or another. As with all stoves. Nothing lasts forever, especially something undergoing large heat variables over time. I have been told quite a few different time spans here, but the range is 15 to 25 years for the most heat sensitive components. Depending on how they were built. And I know some mass heaters that basically broke because of wear and tear, and they were not cheap to fix. That is not to say they are not worth getting or that they are not worth fixing. I am only saying that they do have maintenance costs. And that needs to be factored into any design and fiscal consideration. Hope this helps.

 

[stoveliker]

I think it would be nice to hear how much you burn, per season but also per fire, and how long that one fire heats the space (how large?) it is meant to heat?

A good real world example would be good, given the erroneous "claims" that a few sticks can heat the home for a day...

 

[bholler]

Today, online, anyone can "claim" anything. And exhaust is not the same thing as what is happening along that entire pipeline from combustion chamber to exhaust outlet.

What I can say, is typically mass heaters have a life span. And need to be torn down and rebuilt to some extent or another. As with all stoves. Nothing lasts forever, especially something undergoing large heat variables over time. I have been told quite a few different time spans here, but the range is 15 to 25 years for the most heat sensitive components. Depending on how they were built. And I know some mass heaters that basically broke because of wear and tear, and they were not cheap to fix. That is not to say they are not worth getting or that they are not worth fixing. I am only saying that they do have maintenance costs. And that needs to be factored into any design and fiscal consideration. Hope this helps.

Thankyou for your realistic and objective input on this. I am by no means against mass heaters of any sort. I just don't like the outlandish claims made by some

 

[qwee]

Look at the other mass heater thread - Russian fireplace.....She has one that is over 40 years old. Look at the firebox - there is a picture. Some of the firebrick looks roughed up a bit but still looks functional. Granted this stove couldn't have been worked too hard being on the Southern Oregon coast and by being so large but still it appears to be usable.
Since most masonry heaters are made of masonry materials they should last a long time.

The MHA (masonry heater association) has addressed longevity in their heater designs by requiring a double layer of firebrick in the firebox. When the inner layer wears down it can be 'knocked' out and a new layer of firebrick can be laid in its place. If common brick are used in the firebox or even in the channels that is a different story - you may have cracking issues. And you may even have cracking issues above the firebox on the outer layer of brick or rock - oh well it doesn't affect anything.

 

[bholler]

Look at the other mass heater thread - Russian fireplace.....She has one that is over 40 years old. Look at the firebox - there is a picture. Some of the firebrick looks roughed up a bit but still looks functional. Granted this stove couldn't have been worked too hard being on the Southern Oregon coast and by being so large but still it appears to be usable.
Since most masonry heaters are made of masonry materials they should last a long time.

The MHA (masonry heater association) has addressed longevity in their heater designs by requiring a double layer of firebrick in the firebox. When the inner layer wears down it can be 'knocked' out and a new layer of firebrick can be laid in its place. If common brick are used in the firebox or even in the channels that is a different story - you may have cracking issues. And you may even have cracking issues above the firebox on the outer layer of brick or rock - oh well it doesn't affect anything.

I really doubt that heater was used much at all. Even in regular fireplaces where the temps are far less extreme firebricks deteriorate in 20 to 30 years with heavy use

 

[qwee]

That is why MHA does a double layer brick system in the firebox - out with the old and in with the new. There was a builder who examined some old daily winter use masonry heaters (>30 years old), and found them to still be functional with no need of repair.

 

[john26]

If I wanted a mass heater I would go this route it is UL listed and should be easily insurable if installed per code and owners manual. No its not a rocket mass heater but a mass heater with a 2-3 hour burn time depending on size. In compared to to the rocket mass heater with the steel barrel it has a viewing window that would be important to me. If I didn't want a fire view I would buy a wood boiler or furnace. However look the price and the small amount of rated heating square footage. I could not find anything in the manual or website about actual efficiency ratings or emission numbers as far as producing heat not an actual defined amount of time.
"Soapstone fireplaces burn wood exceptionally clean and at a high rate of efficiency.
This fireplace will spread heat slowly and evenly throughout your home for several hours after it burns out."

my link did not post early
(broken link removed to https://www.valcourtinc.com/en/products/mass-fireplaces/)
what I was getting at is SBI owners of Valcourt does not list any efficiency rating or how long the unit produces useable heat. The unit is UL listed I'm sure SBI has done testing on them it would be interesting to see efficiency numbers from them. With a price from double to six times the price of a quality wood stove if it had outstanding efficiency I would assume SBI would advertise it.

 

[stoveliker]

They do have test reports and a list of tax credit eligible appliances that they sell. The test reports do not contain the FM models (mass heaters), and none (!) Of their models qualifies for the tax credit.

I presume that if the FM heaters would be 75 pct or higher, they'd made sure to list them in the sheet listing only "qualifies" "NO" entries...

Suggesting these masonry (mass) heaters have a poorer efficiency than quite a few stoves on the market now.

 

[rashomon]

Looks like I’m late to this topic, but reading these comments is very frustrating.

Why is no one pointing out the extremely obvious fact that rocket mask heater‘s chimney exit temperature is very low? Everyone is so focused on discrediting the system yet ignoring normal stoves require hot exit gas temperatures just to keep the chimney clean.

The whole point of the rocket mass heater is the thermal mass built around the long horizontal pipe which efficiently pulls the heat to be used in the home, not simply sending it up a chimney.

Everyone here seems educated enough to be debating how many BTUs are potentially contained within a quantity of wood, why aren’t you smart enough to realize one system just makes better use of the heat from the burn. The efficiency is in the entire design.