RMH Combustion air?

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?

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.