Should I use auxiliary heat or emergency heat?
Similarly one may ask, at what temperature should auxiliary heat come on?
Auxiliary Heat. Auixiliary Heat will turn on automatically when heat can no longer efficiently transfer heat from the outside air to heat pump. This is when the outside is around 35-40 degrees and the indoor temperature is around three degrees cooler than the thermostat setting.
Also asked, why is the auxiliary heat coming on?
Auxiliary heat is the electric heat strip in your air handler that is supplemental heat. Auxiliary heat/ Emergency heat help the heat pump keep up when cold outside or the temperature differential on the thermostat is large. Auxiliary heat/emergency heat will come on when the heat pump is in defrost.
Auxiliary heat can handle more extreme temperatures since it uses electric heat strips. What this means, unfortunately, is that it's more expensive than the conventional heat provided by a heat pump. While a gas furnace is not as efficient as a heat pump, it is more efficient than a heat pump using auxiliary heat.