I grew up in the mountains of California, and had two fireplaces in the home. Both were stone with a heatilator in the top. They were supposed to be more efficient that way. One day Dad installed a wood burning stove that protruded out onto the base in order to bring the heat better into the home. It was then probably ten times as efficient as the fireplace. But being in the mountains, there was always snow, and it was always cold. If we waited too late in the year, getting firewood would be nearly impossible once the snowpack had set in. So we started early. Dad had the forestry department come out and mark dead or beetle infested standing trees for removal, and he had a permit to take all the down wood he pleased. We worked hard, and towed it behind the house. We cut up and split about 8-10 cords of wood per winter (one cord is 4' x 4' x 8' of wood. We had a basement beneath the house with outdoor access, so we split and carried all that we could fit into the basement for easy access to the wood stove downstairs. All of those years, and all that work, had I known then what I know now... that you can build a rocket mass heater in your home, and use one tenth of the wood that that wood stove used, let's just say I wouldn't have been in as good of shape as I am now. Why? Because on the fireplace and the wood stove, the majority of the heat all goes out the chimney pipe. We always knew that, but until the rocket mass heater, there was no good way (that we knew of) to draft that heat sideways well and keep it in the home. ~Dave W.
The trick is to mix modern science with knowledge from hundreds of years ago: Burn the smoke; capture heat from the exhaust; focus on the more efficient forms of heat (radiant and conductive heat are favored over convective heat); and, most of all, use a mass to hold the heat for days.
A look at the innards: The fire is at the bottom of the sticks. The strong thermosiphon draft in the riser causes the fire to burn sideways. Rather than immediately extracting the heat, like a conventional woodstove, the heat goes into an insulated area where it gets much hotter. Hotter than molten steel or lava. The sharp turn causes the smoke to mix with the flames, thus burning the smoke. The exhaust is then carried through the mass and outside. More details can be found here.
I am so bonkers about rocket mass heaters that two years ago I did a kickstarter for DVDs of a rocket mass heater workshop! Interest was far greater than I expected. MASSIVE! Wow! So my friends and I have carefully collected a lot more footage and we focused on much higher video and sound quality.