an air source heatpump has a thermostat that cuts the unit off at 37 degrees. beyond that as the temp drops.. the return of heat drops off dramatically.. at this point back up heat comes on.. which if you have electric strip.. you can watch your meter spin and spin and spin.. if you are fortunate to have dual fuel.. where the back up is gas.. you will come out far ahead of strip heating.. This is why gshp is so much more efficient.. some of the newer units are claiming over 27 SEER .. general rule is that one can suck enough heat out of the ground that it provides 4 times the BTU for the draw on the power to run the pump.
the systems have to be sized correctly.. often multiple smaller units.. which are closer to actual heat loads as figured by "j" loading schedule.
But as I am fond of saying.. Conservation is alway a better alternative to running the meter.. Insulation over 20 years is cheap cheap cheap.. and power bills will only be going up up up in Obama keeps up his carbon cr*p which is nothing more than a giant power and money grab enforced by the EPA
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