The purpose of this video is to give folks an idea of how clean the exhaust is while running a rocket mass heater in Missoula, Montana.

When we first start it, there will be smoke.  And there was smoke in the middle of the burn sometimes, but I think that most of that has to do with things that need more design improvements.   For most of the
time, the exhaust was a lot like what is shown in the video - there is fire, but no smoke.   Marci Anderson gets her nose right in there.

Another important thing to note is that the temperature of the exhaust:  see how we have a hot, clean fire burning and guido does not burn his hand when he puts it in the exhaust.  It feels warm, but not hot.  We measured it at about 90 degrees when the barrel was at about 850 degrees.

I show the materials being moved by the freecycles folks from the freecycles HQ in Missoula to Caras Park (downtown Missoula).  Then a bit of building it.

This rocket mass heater is a prototype for some variations.  A wood box shows a different aesthetic, a much taller heat riser design, using dry, loose fill (rocks and sand).  This should be a lighter design than other rocket mass heaters - so it might be good for places that have a wood floor.

This might also be the fastest time a rocket mass heater was ever built:  an hour and fifteen minutes.

http://www.youtube.com/watch?v=kGaGtO8MkQk

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You don't need a rocket stove for a clean burn. My woodstove burns nearly smoke free after the first few minutes of starting it. You'll get a little smoke again when wood is added. Use dry seasoned wood and a properly designed stove and it's all good. Second thing to remember is all the carbon released during burning wood was originaly captured from the air so it's carbon neutral. I use as much dead wood as I can find before cutting any live trees. So far the only trees cut on my land have been those that had to be removed for building the house and driveway.

Here is another video to go with the first:

http://www.makeitmissoula.com/2011/04/paul-wheaton-clean-sustainable-wood-burning/

I think some important things are:

1)  a RMH uses 90% less wood to heat a home, so you have 90% less pollution even if both are burning clean.

2)  a RMH costs less.

3)  a RMH does not need to burn as often.

4)  because of the 90% less wood thing, you use 90% less chainsaw fuel, hauling fuel, etc.  And 90% less hassle in hauling wood into the house.  90% air in the house is used for fires (for those that don't draw air from outside).

Interesting, I saw a thread awhile back where Ernest T. was extolling the benefits of rocket mass heaters, including less time and work in cutting wood. I remember he said that he used small wood and it was necessary to load it fairly often.

Given that I was wondering how it would work out in situations where sometimes you are not home all day, would the thermal mass retain enough heat over that time to keep a home at a reasonable (non-freezing) temperature by the time you got back?

Are they safe to burn while unattended? I feel comfortable leaving my little airtight stove to burn on its own while I am away.

The thermal mass holds heat for days.

My experience with the rocket stove is that since you are burning small dry fuel you pretty well have to nurse it or it will be out of fuel soon. 

Quote from: dug on April 21, 2011, 05:26:59 PM
Given that I was wondering how it would work out in situations where sometimes you are not home all day, would the thermal mass retain enough heat over that time to keep a home at a reasonable (non-freezing) temperature by the time you got back?

Are they safe to burn while unattended? I feel comfortable leaving my little airtight stove to burn on its own while I am away.

We have let ours run unattended for short periods of time, but since it needs to be fed a small amount every hour (or less, depending on the wood), we usually let the fire burn out before leaving, since the draw will continue to pull warm air out of the house and cool down the thermal mass after it's out.

As far as leaving, you'd want a backup source of heat in a very cold climate, as you would with any wood stove.. If all of the mass was warm, I feel like it would take maybe a week in the middle of winter to get the house below freezing here in the U.P., but that's just a guess..

We've been having a little startup frustration from time-to-time now, for a couple of reasons.. The warmer temps now make the draw a little less effective in our temporary furnace-duct-outside-stack, plus we lost the top 5' in some heavy winds.. We didn't know what to build the stack out of the first year, ran out of time and money and just threw up $40 of galvanized 8'' furnace duct, expecting it to eek by the first winter. We just finished our third winter with it, and it's time for a more permanent solution... Wish we could have run the stack up inside the house for many reasons, but the layout doesn't really allow for that..