It is so cold here that my heatpump is running 24 hours a day, none stop. It got down to 4 degrees last night.

The magic number is about 10-15 degrees f. below that the heat pump doesn’t work very well. above 15 the heat pump begins to be more economical. Don’t allow the resistance heat to work above the temperature the heat pump can maintain. When it is real cold outside, the heat pump doesn’t use much electricity, so if it runs 24 hrs, and does the job, that is OK. Do not turn the thermostat back and then back up with a heat pump.