[vreihen16]

We installed an 18,000 BTU air-air heat pump at our little house in the hills. The specs claim that it is good to slightly below 0 F. In reality, it starts to fall behind at around 10-12F, and I can hear the outside fan running full tilt trying to beat every calorie of heat out of the frigid air.

In terms of energy usage, we're probably saving 20% versus our oil-fueled baseboard hot water system. (As the temperature goes down, the savings drop. This is probably where geothermal heat pumps pay off.) At least in the Hudson Valley, we can get away with the heat pump all year...except for the "polar vortex" week or so every winter. We do run the oil system if we are going to be away from home overnight in the winter, because I still have some lingering trust issues about leaving the heat pump unsupervised.

The air-air heat pump works great as a three-season system here in NY State, and I definitely will use it as the primary system if we ever build in SC.....