Although I truly like the above picture someone else may be asking, “What is that?” Although it may appear to be bricks on a mud hole, it is actually the most efficient technology for heating. Paul Wheaton has a great article on how a rocket mass heater works. Also if you are really interested you can contact me, or others, for a workshop or buy some DVD's from Amazon. I’m not wanting to duplicate Paul's work, I want to explain my experiences.
I took a workshop from Ernie and Erica Wisner on Paul Wheaton’s Farm. I was part of the workshop that built the rocket mass heater for the tipi. It was an amazing experience that I recommend to everyone interested in becoming more self-sufficient, be more earth friendly, or just wants to cut less firewood. It was an amazingly liberating experience making cob. Rocket mass heaters are being built without cob, but many other things can be made with cob.
The RMH I helped to build in a tipi during my first workshop used lots of rocks, cob, ducting, and a shippable core. The ducting was primarily HVAC with a few pieces of stovepipe in the initial 10 feet or so. We used rock for the base so that we would not have to make so much cob. A lot more can be learned by following this link, or contacting me.