What about a heat exchanger like this?

http://gravityfeedstoves.com/

This guy has invented and is producing a pellet stove that does not use electricity and has no moving parts (other than the draft control lever and the hinge on the hopper lid). It seems rather clever to me, and the way the burn chamber and heat riser/exchanger is built reminds me of an uninsulated L-rocket tilted 45 degrees. I wonder if a similar kind of heat riser/exchanger could be utilized with a rocket-type woodstove, or if insulating the first 12 inches of his device would improve combustion efficiency. Also, I wonder if his clever method of introducing secondary combustion air could be utilized in a rocket type woodstove.

Thanks for posting this. I want to learn more about this stove. Been kicking around adding a wood stove in the basement.