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