air source heat pumps, though they're improving won't do well in extreme cold; even if they can operate they'll still be running at much lower efficiency. For

air source heat pumps, though they're improving won't do well in extreme cold; even if they can operate they'll still be running at much lower efficiency. For temperatures significantly into negative territory a ground source heat pump would perform far better, where it can draw on a source of heat that will always be at least above freezing. A hybrid system doesn't seem like a bad trade-off though..