Well, I never got around to putting in that automatic, temperature actuated power tube but I still like the idea. I did spend last Friday night up there. It got down to around 6°F and the new stove configuration was much more controllable in terms of heat output. The building warmed up pretty quickly (2 hours to 60°F) Then, even with more coal in there I was able to throttle it down and get less heat output than the old configuration. The extra capacity and slower burn rate got me right through the night without having to reload. It was ashed up pretty well in the morning but the new coal I put in lit off quickly. The best news is that the building was 72°F when I got up with a window cracked an inch top and bottom. I'll probably need that power tube for warmer weather.