Answer: I always recommended to my customers if the temperature out side is 20 degrees or below for more than 2 days straight, then switch to emergency heat because all that you are doing is getting a vicious run cycle where the heat pump never shuts off. The heat pump thermostat goes back and fourth between auxiliary heat and heat pump. The temperature is never satisfied in the heat pump cycle so you get into a run all, constant run all the time mode. This is very hard on your outdoor heat pump unit and will shorten the life of your heat pump. This is one reason my most heat pumps only last about half as long as air conditioners because they run in both summer and winter. My suggestion is to only run in regular heat pump mode when the temperature in above 20 degrees out side. It the temperature outside is below 20 degrees for an extended period of time go into emergency/auxiliary heat. This might run up your electric bill, but you will be warmer and it will save your heat pump from failing too soon.
