Instructables
Picture of How to build a Rocket Mass Heater
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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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katou6 months 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!
djuan16 months ago
very cool would love to try this
jxrgen6 months 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)  jxrgen6 months ago

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

pfred26 months 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)  pfred26 months 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.

blkhawk6 months 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!

good job!

Southernelle5 months ago

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)  Southernelle5 months 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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Beerdedbeast6 months ago
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.
ecarter116 months ago

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

DeeRilee6 months 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)  DeeRilee6 months 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.

kleinjahr6 months 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_om6 months ago

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

AtOurOwnPace6 months ago

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)  AtOurOwnPace6 months 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.

frogier6 months ago

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

velacreations (author)  frogier6 months ago

Thanks. Have corrected the oversight.

richardgreco6 months ago

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)  richardgreco6 months 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.
chuckyd6 months ago

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

moosescat6 months 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)  moosescat6 months 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 Solar6 months ago

sweet twist on the Russian Stove. 2 thumbs up

Todd Gehris6 months ago
What kind of burn time do you get on this? If you load it will it burn through the night?
velacreations (author)  Todd Gehris6 months ago

No. If you you load it, it will burn out in a couple of hours. However, the heat does last through the night.

Cool thanks. I had thought maybe it would stay warm with all the bricks. Would this stove work as well if the loading area was on the side instead of the top?

velacreations (author)  Todd Gehris6 months ago

The point of having the loading area on top is that it's gravity fed and thus super easy - no opening of doors or pushing the wood in, you just stick chunks in the hole and they fall down as they burn up.

abraxas16 months ago
I'm interested in replacing my wood stove with a rocket stove but the I trade my wood pile for a pile of sticks?
How big is the pile of stocks I need that would last as long as 2 cords of wood?
Thanks so much. Very helpful.
velacreations (author)  abraxas16 months ago
you don't have to trade the wood for sticks. As long as your wood is split to fit into the stove, it will burn. Your usage will vary according to your climate.

Very cool stove!

You might consider lightly sanding the metal surfaces and painting them black. Matte black surfaces emit heat (infrared light) better than shiny surfaces. (It has to do with the concept of black-body radiation, and the fact that good absorbers of light also make good emitters of light.)