You don't say what your aux heat is - gas or electric.

You should use your heat pump all the time. Once you switch to aux heat, your electric cost increases 3x (assuming you have electric resistance back-up).

If it is snowy out, the heat pump will defrost more often if you have demand defrost. If you have time-initiated defrost, the heat pump will defrost according to the pre-selected time (30, 60, or 90 minutes).

From Goodman's website, for my 14 SEER 3 ton heat pump:

Outside temp = 30, Delta T = 23.4 degrees, COP = 2.98
Outside = 20, Delta T = 20, COP = 2.65
Outside = 10, 16 degrees, COP = 2.26
Outside = 0, 13 degrees, COP = 1.84
Outside = -10, 9 degrees, COP = 1.35

This means that even at -10 F outside, the heat pump is putting out 79 degree air (70 room temp plus 9 from the heat pump) and is still 135% efficient as compared to electric resistance heat.

Along with a drop in output temp, the heat pump draws less KWs as the outdoor temp drops. My unit draws 2.64 KWs at 30F, 2.41 KWs at 10 F. 10% less power.

Many people turn off their heat pump at brutal cold temps because of concerns about wear-and-tear from it running non-stop.

matt

I am going to assume that you have strip heat backup not fossil fuel backup. If that is the case, then I agree completely with Gary. However, if you have ice buildup on your outside condenser fan/blades, then you might consider deicing the blades with warm water or going to emergency until ice on fan blades melt. You may want to contact dealer and get their recommendation on a situation like this.

IMO