So far, I haven't seen this very simple idea mentioned elsewhere, so I'm throwing it out for those who may be interested to try it. It seems that the draft through a small wood furnace might be controlled to govern the burn rate and help control temperatures in a living space. The idea is to control the position of a damper with an automatic greenhouse window opener. If properly calibrated, then it seems this might serve as a simple mechanical thermostat to control temperature in a living space. NOTE: A small furnace is certainly required to achieve an efficient burn at a low rate.
I've considered another idea that might interest some here. A very small "rocket mass" type system w/o a thermal mass might work where a small barrel is insulated and with a steam generator tubing coil used to cool the combustion gases in lieu of the barrel wall. I believe this can create a strong draft for even a small system. In this case steam is distributed to a more or less conventional radiator.