The best bet here would to be make a small tile- or oven stove. The idea is to build a small, very hot fire in it, to thoroughly incinerate fuel with minimal exhaust, which heats up a material with a high infrared emissivity. Then for a few hours, the room it is in is illuminated with IR.
The idea would be to have a stove that weighs about 200 pounds, is inexpensive, consumes far less fuel than a typical stove, and while it’s not for cooking, it keeps their home warm.
Mechanicos had this link upthread. Looks intersting.
“build a small, very hot fire in it, to thoroughly incinerate fuel with minimal exhaust, “
http://www.richsoil.com/rocket-stove-mass-heater.jsp