I just helped build one of these, and I’m pretty excited about it. You can build them from scavenged materials, with minimal tools, and you end up with a woodstove that uses one tenth the wood of a normal wood stove.
All you need are some bricks, a steel drum, clay, sand, urbanite (concrete chunks), stove pipe, and vermiculite, or some other insulator.
Here’s the basic idea: You have an insulated burn chamber, which burns the wood really hot. Most stoves aren’t hot enough to give a complete burn, which doesn’t utilize the potential in the wood. Rocket stoves burn hotter than a monucka.
The smoke then goes up a mini chimney inside the steel drum, then goes back down into your stove pipe. This little heat riser is how you propel your smoke horizontally through your dwelling.
The smoke then goes through a cob bench, bed, floor, or whatever, as long as it has thermal mass. Almost all the heat from the smoke is transferred into the cob. With most woodstoves or campfires, most of the heat is lost into the atmosphere.
If you want to build one, you can get the book here: http://www.cobcottage.com/node/214
The thought of billions of people switching to heating by fire is a little frightening. These little suckas are going to be essential.