Rocket Mass Heater — 10 December 2013

A rocket mass heater is a heater that is supposedly supper efficient at combustion and is able to heat a home with much less wood and pollution than a conventional wood burning stove or fireplace. I’ll say at the get go that I’m a little skeptical about a lot of the claims that I have been reading on-line, such as:

  • heat your home with 80% to 90% less wood
  • Use twigs instead of wood to heat your home
  • exhaust is nearly pure steam and CO2
  • 90% efficient at burning wood
  • the heat from one fire can last for days
  • you can build one in a day and half
  • folks have built them spending less than $20



There is a lot of discussion of different designs on the web. I started looking into it at the beginning of the month, and I was “hooked”. I had to give it a try.

To explain what a rocket stove mass heater is, I’ll first start with a rocket stove. The rocket stove consists of a j-shaped insulated channel.

Once the insulated “heat channel” gets warm, the warm air rises and creates a draft up the channel. The heat riser gets very hot, which helps burn more of the gases of combustion, producing more heat from the same fuel. You can place your pot of water (or whatever) on the top of the heat riser, and the concentrated heat will soon supply enough heat to cook with.

rocket stove

The rocket mass heater takes the rocket stove concept a step further. A barrel (or “bell”) is placed over the heat riser with a small gap (about 1.5 inches) between the top of the heat riser and the interior of the bell. This forces the hot air and gas to return down the outside of the heat riser.


The theory is that a heat torus is created near the top outside of the heat riser where hot temperatures continue to combust gases. The steel bell has the effect of capturing the heat which is then radiated into the room. To capture the most heat, the exhaust is then run through ductwork that is surrounded by a thermal mass that further transfers the heat before the exhaust is expelled outdoors. The designs (that I have seen) use cob furniture as the mass structure.

(A great design drawing I found on

(A great design drawing I found on

Here are some actual rocket mass heaters that have been built.





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(7) Readers Comments

  1. Wow, seeing the large sized rocket heaters inside an actual home is pretty impressive! Good luck Ben…try it outside your house first though 🙂

    • Yes, Its likely that my home insurance company would frown on putting a RMH in the home. I’d like to put this in an aquaponics greenhouse though.

  2. I’ve never heard of a rocket mass heater. I’m most interested in hearing how yours turns out!

  3. I have seen some chat on rocket stoves and pictured what some of us probably used to heat charcoals up to grill with. A pipe with a handle that you loaded charcoal on top a screen and stuffed newspaper in the bottom and lit the paper. I guess I was close. Being out in my shop tonight made me look at this. I need a heat source out there.. It sounds very much like a shepherd’s stove where you heat the stove with a fire on the side of the box then pull a damper up to force heat down and up on the other side of an oven to get as much heat out of the fire before it gets to the stove pipe. I will be interested to see what you come up with.

  4. Looks exciting! I agree with Spencer–Try it outside first:)

  5. Pingback: Rocket Mass Heater – Phase 1 |

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