Three words, insulate, insulate, insulate. I have 2100sf on the main floor, 15' ceilings+700sf of loft area. R-19 walls, R-57 ceilings, all fiberglass batts, heat with a 120k btu, 96% efficient propane furnace. Looks like this winter I will use around 400gal of propane for heat. I keep the shop...