The one on the left is just an extremely simple version of an ordinary stove. The one on the right is a rocket stove. But to make it mass heater, I guess it should have a horizontal channel circulating the hot air, heating up the mass surrounding the channel. I'd like to try something like that for heating up the bathtub, but didn't have enough time to test it this summer. Maybe later =)

Ah, and I know a little about permaculture. After the University I've felt "mentally exhausted", very slow to read new stuff. I like to learn by just doing things, with trial and error, and then reading a bit here and there to get further ideas.

More of the story of this picture is told here:
http://www.enormouselk.com/?q=erkkasblog/friends-and-fireplaces