Why dont we all want rocket mass heaters?

[paul wheaton]

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.

 

[electrathon]

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.

 

[paul wheaton]

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.

 

[twd000]

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

 

[bholler]

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.

 

[electrathon]

@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.

 

[byQ]

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

 

[georgepds]

@byQ

Links to test data please.

 

[byQ]

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

 

[byQ]

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.

 

[georgepds]

Here are a few.

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

Thank you

 

[twd000]

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.

 

[twd000]

...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

 

[georgepds]

...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

 

[simple.serf]

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.

 

[paul wheaton]

@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.

 

[paul wheaton]

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 ....

 

[bholler]

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.

 

[bholler]

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.

 

[Seasoned Oak]

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.

 

[paul wheaton]

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.

 

[bholler]

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???

 

[paul wheaton]

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:

 

[paul wheaton]

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

 

[bholler]

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???