Auxiliary heat is the supplemental heat source that helps a heat pump when it cannot meet demand alone, typically electric resistance heat strips in the air handler or a gas furnace in a dual-fuel system. It engages during very cold weather, defrost cycles, or large thermostat setbacks. Emergency heat runs the backup alone, without the heat pump.
Why it matters to you
Electric heat strips use roughly two to three times the electricity of the heat pump for the same heat, so backup heat that runs more than it should shows up on a BC Hydro bill. In the Fraser Valley's mild winters, a correctly sized heat pump should need backup heat only occasionally.
Practical guidance
Avoid large thermostat setbacks on a heat pump, since a big recovery can call for backup heat; a heat-pump-compatible thermostat helps. If the aux heat indicator stays on for long stretches in mild weather, have the system checked.