"Have you looked into permies.com and the rocket mass stove that is advocated there?  They talk about how damping a fire down makes the stove less efficient.  And their design lets it burn hot but slowly release the heat."

--- Phil, in response to yesterday's post

We actually get this question a lot, so I thought I'd answer in a post so I can point later readers here.  For those who aren't familiar with rocket stoves, they were developed as an efficient cook stove for countries where folks still largely heat their food with wood.  The design channels all of a fire's heat into a very specific area around a pot and uses preheating of the combustion air and insulation to achieve high efficiency with low cost materials.  One of these days, we may build a rocket stove for summer cooking, but since I spend so much time processing all of our homegrown produce, I don't think I'd have the patience to use a higher work stove at the moment.

Of course, that's not what Phil was talking about --- he wanted to know why we don't heat our home with a rocket stove.  While I don't have the data to back this up, I suspect that our scientifically designed, high efficiency wood stove is a more effective space heater than any homemade rocket stove we could come up with.  Our little Jotul uses the same preheating and insulation concepts as the rocket stove, and I can attest to the fact that the smoke coming out the chimney is usually completely clear as long as I'm burning dry wood.  We also burn a fraction of the wood our neighbors do.

On the other hand, Phil is completely correct that you get more efficiency from any fire if you burn it hot rather than damping it down --- that's why we chose a small wood stove that fits our small space and burns little chunks of wood on "high" all day.  However, heating with a wood stove overnight requires you to damp the stove down (unless you buy a pellet stove, which doesn't seem very sustainable to me).  A rocket stove would be a very bad option for overnight heating since the ones I've seen require you to feed small pieces of wood into the stove very frequently --- I prefer to damp her down and sleep.

What does make sense for overnight wood heating is adding more thermal mass around any kind of stove.  This is how the rocket mass stove (the heating version) works --- a huge mass of masonry stores heat while the stove is running during the day, then radiates that warmth back into the room when the stove burns down.  Our trailer has weight restrictions, so we can't go overboard with massive cob-type stove surrounds the way some folks do, but one of these days I do plan to tile the living room floor to capture the great passive solar heat coming in our south-facing windows on winter days.  Our slow but sure progress on insulating our space will also help.