These are definitely interesting, kind of have to build your house around one though.

We currently use a wood stove that uses a catalytic combuster, so actually reburns the smoke for even more heat. Silly efficiency and almost no particulate matter so passes even the most stringent environmental laws. Its actually one the greenest ways to heat a place like ours. (it only heats the main living area though, we use small space heaters for bedrooms downstairs)