Heat Pump Emergency Heat: What It Is and When to Use It

Most heat pump thermostats have a setting called EM HEAT or emergency heat. It's easy to misunderstand, and running it by mistake can make your electric bill jump.

Auxiliary heat vs emergency heat

Auxiliary heat kicks in automatically when the heat pump needs help, like during defrost or when the house is far below the set temperature. It turns off on its own.

Emergency heat is a manual setting. It shuts the heat pump off completely and runs only the backup heat, usually electric resistance strips or a gas furnace in a dual fuel system.

When to use emergency heat

• The outdoor unit is damaged, iced over and not clearing, or not running
• A tree limb or storm damaged the outdoor unit
• You're waiting on a repair and need heat in the meantime

When not to use it

Don't use it just because it's cold out. On electric strips, emergency heat costs much more to run than the heat pump. Use it as a stopgap and call for service.

Why the AUX light is on

Seeing AUX or auxiliary heat on the thermostat now and then is normal, especially on cold mornings or during defrost. If it runs constantly, the system may be undersized, low on refrigerant, or struggling. Here's how to troubleshoot.