I was wondering what you guys think of this. As the Rocket Mass Heater burns it needs air, this air generally comes in through the doors and windows, i.e. draft, since air is going to come in no matter what and we actually need the air why not use it. Below is attached a rough drawing of a 2" pipe coming from the outside, the air is heated as it passes by the bell and exits the pipe over the bells top. The advantages are that the air coming in to feed the mass heater is now hot rather than cooling down the other areas, it should increase warm air circulation and might even create a positive pressure inside.