Similar story to the other two in this thread- air exchange heat pumps are available that are rated to work below 20* F. In the end, I switched to wood (natural

Similar story to the other two in this thread- air exchange heat pumps are available that are rated to work below 20* F. In the end, I switched to wood (natural gas isn't available where I am, and propane is expensive). Currently using a high efficiency stove and a gassification mass heater. Our central heating barely turns on in winter at this point, and the thermal efficiency of both systems isn't too far from the propane furnace either. (The mass heater is stupidly efficient, the wood stove only in the 85% range I think).