[MrB]

With a rocket mass heater, you run the insulated chimney up inside an inverted 55 gal metal barrel then an exhaust pipe back down around the base. You exhaust the gases out through a mass of bricks, gravel, adobe, etc which absorbs the heat, then finally run the exhaust outside.

[MrB]

Here's one. You can see what's going on to a certain extent:

[Kartographer]

Understood, but was think of something non-permanate that could be put together easily in an emergency.