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Emergency heat

Emergency heat is a thermostat mode that turns the heat pump off and heats with the backup source only.

Editorial staffEdited by heatpumpwiki

History 1

Emergency heat (often "EM HT" or "EMER" on the thermostat) is a mode you choose by hand. It locks out the heat pump and heats the house with the backup only.

Rheem describes it as "a back-up heating mode to be used only if there is a suspected problem with the outdoor unit," in which "the outdoor unit will be locked off."Source 1 Lennox: "In EMERGENCY HEAT mode, all heating demand is satisfied by auxiliary heat and heat pump operation is locked out."Source 2

With electric resistance backup, emergency heat costs more to run than the heat pump. Use it until the heat pump is repaired, then switch back. Compare Aux heat (auxiliary heat) and see Heat pump backup heat and lockout temperatures.

Sources

  1. 1.Outdoor Heat Pump User's Information Manual (708163B). Rheem. Accessed Oct 25, 2026
  2. 2.Heat Pump System Information, User Guide (507657-01). Lennox. Accessed Oct 25, 2026

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