Nathan Lewis : You are not the 1st fellow member of Permies dot com to think along the exact same lines you are following,
Please understand that a properly functioning Rocket Mass Heater works only because of the Freaky high temperatures that it 'Fires' at ! - 1000 º F
Note that 212 º ƒ is the temperature at which Water Flashes to Steam !!! As such there is an inherent danger close to the Historical event of the
" Boston Marathon Bombing" - only with more fatalities, and more full thickness, full body burns !
Below is a link to one of the very few generally safe Rocket Mass Heater RMH fired hot waterheaters !