Hi Patrick; Do you have a copy of ianto evans book
rocket mass heaters ? If not, you
should invest in one. it is readily available on line, it will
answer alot of questions you may have . Are you wanting to build a
rocket stove in your sauna or a rocket mass heater ? A rocket stove would definitely heat a sauna as well as boil
water but be careful, rocket stoves get red hot very fast it could burn your sauna down if its not isolated from burnable surfaces. You can also cook on a rocket stove, that is what they were designed for. I would build a
rocket mass heater for a sauna rather than a rocket stove ,so the room stated toasty for a longer time , and you would have a nice heated bench to lay on . Asking specific questions on this site will get you responses quicker than a general question will. Good luck with your build Tom