Paul Wheaton: I have answered the “what is a rocket mass heater?” question hundreds of times. This is my attempt to make a very short answer. Sure, there is a hundred times more info …. maybe a thousand times more info … but the function of this video is to give a quick idea of what it is. We start with the idea of a conventional wood stove. The fire is typically around 1000 degrees F. Heat is extracted immediately. Smoke goes up the chimney due to a thermosiphon. This design has the problem of creosote leading to chimney fires. So if you insulate the chimney, the chimney gets hot enough that the creosote burns much more often – thus reducing the risk. But the downside is that more heat leaves the house through the chimney. We shift the design to insulate the fire box. With temperature now at 1800 degrees F, the creosote and the smoke are burned. The exhaust is mostly steam and CO2. We can now safely extract more heat. We add a stubby chimney so we can push the exhaust wherever we want. We add a mass to absorb heat. That’s it. A rocket mass heater. And then we add some pictures of pretty rocket mass heaters.