My 2-year-old Trane heat pump is connected to a 20-year-old Amana air handler with resistance emergency heat elements. The system is heating and cooling a 1600 sq. ft. townhouse condo. The serviceman suggested that I manually switch to emergency heat when it's "very cold" to shut down the heat pump and go resistance-only, on the theory that the heat pump is working so hard that resistance heat would be more efficient. However, he could not say what "very cold" was--he speculated that it was in the teens. I know that when it's that cold, my heat pump tends to run more than half the time, with very low heat rise at the registers, but I have not seen it kick in the emergency heat automatically.
Is there a way I can estimate the break-point outside temperature for heat pump vs. resistance heating? Or is there a "rule of thumb"?
Thanks for any suggestions.