It seams that the RMH i have seen all get combustion air from inside the desired heating area. I have a freestanding wood fireplace that gets it's combustion air from outside the desired heated space. Has anyone designed a RMH that will get combustion air from outside the house, shop, greenhouse that it is trying to heat? it seems that there might be a lot of heated air going up the "chimney" so to speak and maybe outside combustion air might be more efficient? I have not made a RMH but would like to put one in a hoophouse in central N.C. for next winter and was wondering if it would be worthwhile to spend time on the combustion air issue?
The argument lies in having outside air draft into the room naturally or piping the cold air directly into the RMH. The first would keep the room temp slightly lower where as the second would keep the burn temp slightly lower, making the RMH work harder. The balance is in having the outside air piped in somewhere through the mass thus preheating the air but taking heat from the thermal battery to do so. Alternatively, aluminum ducting hung high in the room could transfer just enough heat into the incoming outside air to keep the fire at max temp while not adding a chill to the room. As far as having all that in a greenhouse seems a bit much. That's my take ($.02)
P.J. : you got 1/2 an answer before, and that Is subject to change as tomorrows Rocket Stoves get more efficient/come up to temps. much more quickly !
the 2nd half of the story deals with what happens to that heat trapped in the make up air your Rocket Stoves uses to burn your fuel wood.
basically, that heat is re-radiated into the room through the surface of the 55gal drum, or is taken up by the thermal mass and stored for later Radiation ! hope this helps PYRO _ magically Allen L.
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