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There are two main factors that differentiate a Rocket Mass Heater (RMH) from a regular wood-burning stove. One is that the combustion that takes place is far more complete in an RMH, due to the increased draft and insulated burn chamber. An RMH can consequently be up to eight times more efficient, requiring less wood for the same amount of heat. This also results in there being less ash and smoke.
 
The second factor that makes an RMH so superior is the thermal mass that encases the components that heat up. As biomass is burned and the RMH is heated, it transfers heat to the thermal mass (adobe, dirt, sand, even water). Although it takes a while to heat up, that heat will last hours after the fire has been extinguished. For example, if we have a fire going for just a couple of hours in the evening, the stove will still be hot in the morning.
 
By the time we started researching the benefits of an RMH, we had already built our house and had a regular wood-burning stove in place. If we’d known about it sooner, we would have built an RMH encased by an adobe bench or something similar into the design of the house. We made the RMH we’ll be describing in this article to fit an existing space, and it has been working great!
 
As long as the sun comes out in the day, we rarely need a fire, as we designed the house to make use of solar gain. However, for those cloudy, cold days, this stove has been a huge hit. We use a fraction of the wood we used to, we can burn a far greater variety of biomass, and the heat lasts a lot longer. It’s win-win all around. The only disadvantage is that it takes more work to make one than just going to the store and getting a pre-made stove, but it seems like a relatively small price to pay, especially for the Makers out there.
 
If you use wood to heat your house, you should definitely consider making a RMH. It will make a huge difference to your home and your woodpile. This design can be modified to suit your space and needs. Or you can use the principles we outline to create your own unique heating device.
 
All in, it cost us $150, though an adobe one would be considerably cheaper. Still, we’ve made that money back in the time and energy saved in collecting and cutting firewood.

This RMH is based around a 6” diameter flue.  If your house has a different flue size, then components will have to be rescaled.  The cross sectional area of all parts of the system can be no bigger than the cross sectional area of the flue.  The burn chamber (the horizontal area where the flame is) should be the smallest cross sectional area of the entire system.  The greater area you have, the taller the heat riser should be, as well.  So, if you do build one of these, follow these plans exactly or research what things may change with a different flue size.

For more of our ideas and projects, please visit our site.

How to build a Rocket Mass Heater
 
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katou1 year ago
This is a pretty decent application of the rocket stove design principles pioneered by Aprovecho! Winiarski (the inventor of the rocket stove) would be pleased to see your interpretation I'm sure!
djuan11 year ago
very cool would love to try this
jxrgen1 year ago

That is a very nice project and instructable! I have been wanting to build a rocket stove for a while now and your model here seems to be a direction that I might move towards. Do you know the weight of the complete stove?

velacreations (author)  jxrgen1 year ago

Sorry, no idea about the weight. With thermal mass though, you do want it fairly heavy.

pfred21 year ago

This thing seems complicated. I think I need some kind of a diagram to try to conceptualize this whole thing. I've heard of rocket stoves. I need to build something for my garage workshop for next winter here. I already have a chimney. Although why I've no idea. It was here when I moved in. This winter convinced me that I need to hook something up to the chimney too. It's been cold!

velacreations (author)  pfred21 year ago

Great idea. We've now made a diagram and placed it the main intro step. Click on it to make it bigger. Hope it helps.

RMH stoves really are worth the time and effort. They are so much more efficient, and we wish we'd known about them sooner.

After I posted my comment I did a web search to see some diagrams. Yours helps here too thanks.

blkhawk1 year ago

I have seen some clips and blogs about rocket mass heaters and your design is the best. I like the use of sheet metal and firebricks. Great job!

Judylimlim1 month ago
I need help with my rocket mass heater, any one with experience can help me in Boulder, Colorado ! Thank you!
cdstudioNH made it!4 months ago

I didn't make it, my friend did, but I just posted an Instructable on how to light one. Yours is a Very nice version of a rocket mass heater!

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gjh425 months ago

After a whole heating season, how has this heater held up? A metal heat riser, even 1/4" thick, is known to corrode and buckle fairly quickly in the heat and atmosphere of the burn tunnel and riser if it is burning efficiently. It would be very helpful to know what the condition is and how long you foresee it lasting in this incarnation.

chuckyd1 year ago

It is legal to put a wood burning implement against the wall?

Nothing about a Rocket Stove is Legal. The question is, "is it safe?" And that depends on what the wall is made out of.

velacreations (author)  SeanDieselBirger6 months ago
That depends entirely on the jurisdiction. We don't have regulations on wood burning devices, here.

In our case, the exterior of the rocket mass heater doesn't exceed 150 degrees where it touches the wall, and the wall is reinforced concrete. So, the "safe" factor is pretty high.

I most places in the US, a masonry heating device that weighs more than 1700 lbs is exempt from EPA regs. As far as fire protection goes, depends on the building codes in your area. My county uses International Building Code.

Klimaatcombi5 months ago

The tip ti use sand instead of cob I will certainly use. Thank you.

ErinKS9 months ago
So, we are trying to make this. We have followed the instructions, as closely as possible in our house, but we still get smoke coming out from both the burn tunnel and the exhaust. What do you think might be the problem?
velacreations (author)  ErinKS9 months ago
I imagine you have a restriction somewhere. Try using a fan and measure the exhaust air coming out of your unit, just to see if air is moving through properly.

There are a few places that a restriction can take place. One is in the exhaust tubing itself, especially if it was bent or squeeze at any point during the sand fill. Another is where the air around the heat drum meets the exhaust going out of the house, at the bottom right of the unit.

Good luck, and let us know how it goes.

If I wanted to make a nicer looking one for my shop and for a new house...do you also have directions for the ceramic or terracotta one? or would they be as good as this one? We are planning on building my woodworking shop first and live in that then build the main house. Gas is far too expensive to use. Also would you recommend this for tiny houses as we are thinking about building one of those as a guest house? I love the detailed photos. and instructions... thanks!

velacreations (author)  Southernelle1 year ago

This would definitely be great for a tiny house. You wouldn't need to run it for very long, and the thermal mass would then keep the small space warm for a long time.

If we were to design one before we began to build, we would allocate space for an adobe bench as the thermal mass. In the first house we built, we made a fireplace/oven out of adobe/cob and sculpted it as a tree (see photo). It is a material that allows for creativity, and coupled with the RMH principles, it would be the most striking option.

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Hi what do you estimate the weight of this rmh heater?
sorry not the tree one the sheet metal and brick one pls

good job!

Most insurance companies will not insure a home with a home/hand made heating device no matter how well you construct it. If insurance is of no concern build on.
ecarter111 year ago

Hi, do you have any plans for this it looks great?

DeeRilee1 year ago

Would you be able to tie into an existing chimney? My house used to have a wood stove in the living room & there is a chimney on the outside of my house. At the present time there is one of those removable caps covering the hole in the wall that the stovepipe attached to.

I'm sure the chimney needs to be cleaned out (and the chimney swifts evicted), but it is in good condition otherwise.

velacreations (author)  DeeRilee1 year ago

Yes, you could tie into an existing chimney. The most important factor to consider is the size of the flue/stove pipe. This design is based on a 6" diameter flue. If yours is different, you will need to adjust the size of the burn tunnel and heat riser as they are all precisely related.

kleinjahr1 year ago

Nice build. Heat source looks a bit close to the wall, no problems with heat transfer? Any problems with local building inspector or insurance?

T_om1 year ago

Sounds like the perfect recipe for a chimney fire after a while. Even with very complete combustion. How is the thing cleaned?

Great 'able. I've been reading about RMH's for years on permies.com. Did you do anything about insurance? I want to build a RMH in our house but I keep getting hung up on the insurance component. "You burned your house down with an unapproved heating device, therefore your claim is denied." I really don't expect to burn my house down, but if something did happen I can imagine a response like that from the insurance world.

velacreations (author)  AtOurOwnPace1 year ago

The only exposed parts that get hot enough to cause a fire are the hot-plate and the actually logs. Keep anything flammable away from them, and maybe build a hopper for the fuel (so it couldn't ever fall out), and you should be fine.

We built our house out of concrete and brick, so we don't often consider the dangers of fire as far as the house is concerned. However, we do have small kids, and so all the parts that they might brush against accidentally are surrounded by thermal mass and won't actually burn the skin.

frogier1 year ago

Um, I think you forgot to mention welding equipment under "tools"...

velacreations (author)  frogier1 year ago

Thanks. Have corrected the oversight.

Nice tutorial. I would believe that RMS is more efficient at burning. But, the weight of my steel wood stove is >400 lbs. When it gets hot, it stays hot for a long time.

velacreations (author)  richardgreco1 year ago
that may be, but I'd venture to say there's at least 3 times the weight in this heater, maybe more. The more mass you have, the more thermal storage.
moosescat1 year ago

Sixty years ago my parents heated their home with sawdust in a stove similar to this. It had a hopper for the sawdust that sat where the fuel opening is in this model. It would hold fire in -30F overnight if you filled it at bedtime and set the thermostat back to 60F. We sometimes burned it continuously for a month without removing ash. We lived in timber company and the sawmills were so anxious to get rid of sawdust that they would even load it for you. Then someone invented particle board and sawdust wasn't free anymore.

velacreations (author)  moosescat1 year ago

Exactly right. You can also use chipped up trimmings, corn cobs, and all sorts of things. The hopper is a useful addition when burning finer particles than split wood and twigs.

A very similar system (plus filters) can be used to power gasoline engines (both stationary and vehicles).

Dark Solar1 year ago

sweet twist on the Russian Stove. 2 thumbs up

What kind of burn time do you get on this? If you load it will it burn through the night?
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