Checked into “rocket mass heaters” tonight, very interesting. Thanks!
Then you will probably be interested in the following. Matt also runs the permsteading discussion board. Lots of good info and ideas there.
Rocket Mass Heater Cast Core Build
https://www.youtube.com/watch?v=7ANMXGrxgnE
Rocket Mass Heater Cast Core Part II The Heat Riser
https://www.youtube.com/watch?v=AqvTdbRSlwk
Matt’s Channel
https://www.youtube.com/user/broaudio/videos
And see the comments of Ken Peavey in the following (foreman and sometimes field supervisor for an industrial refractory contractor)—very good info on casting.
http://www.permies.com/t/21815/rocket-stoves/castable-burn-chamber
New core builds are often tested outdoors first when feasible, areas around units are relatively fireproof (floors, clearances, fireproof barriers, smoke mitigation, extinguishers, smoke alarms, carbon monoxide alarms, etc.).
The Ma$onry Heater A$$ociation is also interested, of course (dollar signs because of Mechanical Code requirement for certified builders).
http://www.handprintpress.com/home-heat/recent-research-on-rocket-mass-heaters-and-bell-design/