I conducted an interesting experiment last winter. Adapting a proper flue to our old smoke dragon insert proved too difficult, ultimately because the insert's 5 x 15" outlet was overlaping the lintel by ~ 1". So I put a pair of $40 electric radiators in the room. These things run a 600W element, a 900W element, or both, for 2000, 3000, or 5000btu. Most days, I ran the 2 heaters @ 3000btu for a total of 6000btu. Guess what. This kept the room in the low 60's, which is all the smoke dragon ever did unless I shoveled wood into it on a cold night when the draft was good. Looking back now, I'm not surprised by the dragon's relatively poor performance. . .typical "slammer" install into an exterior chimney. I guesstimate it was running ~ 30% efficiency. What did surprise me was that 5000 - 10000btu was an adequate amount of heat most of the time, probably because I left them on almost continuously, so the house was always preloaded with some heat. So I got to thinking, and reading, and thinking some more. . .