The emergency heat on your furnace ensures that, should a major heat pump component fail, you won’t be stuck in a cold house on a chilly night. Like most backup functions, the emergency heat on your furnace is designed to be a temporary stopgap measure to provide heat for a limited time until your heat pump can be repaired.
While automatic supplemental heat and emergency heat both utilize the same backup heat source — electric resistance coils built into the indoor air handler — they’re engineered for very different purposes:
Supplement Heat
Supplemental heat activates automatically when outdoor temperatures drop below the heat pump’s rated capacity to extract sufficient heat energy. A controller in the heat pump senses the reduced heat energy and temporarily energizes the electric coils to generate supplemental heat.
Once outdoor temperatures warm up to the heat pump’s specified range, the controller turns off the supplemental heat, and the system reverts to heat pump operation. In supplemental heating mode, the thermostat normally displays “AUX” for auxiliary.
Emergency Heat
The emergency heating mode utilizes the same electric coils to generate heat as the supplemental mode. This mode is used only when a major heat pump malfunction disables your unit. In this case, supplemental heat will not automatically activate. Emergency heating is manually activated by the user, normally by selecting the emergency mode via thethermostat. The thermostat typically displays “EM” when emergency heat is selected.
When an Emergency Occurs …
Supplemental heat automatically cycles the heat pump in and out of supplemental heating mode, using electric heating temporarily. However, because it’s activated manually, emergency heat continues to energize electric heating coils until it’s manually switched off again.
Because electric heating is much more expensive than heat pump operation, leaving the unit on emergency heat substantially increases operating costs. Always call an HVAC service professional ASAP when a heat pump failure occurs in order to reduce your reliance on emergency heat.
For more information about the proper use of emergency heat, contact Around the Clock Air Conditioning & Heating in Los Angeles.
Our goal is to help educate our customers in Los Angeles, North Hollywood and surrounding areas about energy and home comfort issues (specific to HVAC systems). For more information about emergency heat and other HVAC topics,download our free Home Comfort Resource guide.
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