What Is Auxiliary Heat?

Auxiliary heat is the backup heating source a heat pump calls on when its own output cannot meet demand — usually electric resistance strips in the air handler, or a furnace in a dual-fuel system. Emergency heat is a separate manual mode that runs the backup alone, bypassing the heat pump.

Also called: aux heat · emergency heat · backup heat · supplemental heat

Why it matters to you

Electric resistance heat converts one unit of electricity into one unit of heat, with none of the multiplier a heat pump provides, so hours spent on auxiliary heat consume markedly more electricity for the same warmth. On the coast, a system calling for aux heat in mild weather is a signal worth investigating.

What to do about it

Leave the thermostat in normal heating mode and let it decide; reserve Emergency Heat for an actual heat-pump failure. Large thermostat setbacks can trigger aux heat on recovery, so modest, steady settings tend to keep it off.