You should turn on emergency heat only when your heat pump can’t safely or reliably run in its normal mode, and only until a technician can fix the problem.

What “emergency heat” actually is

  • On a heat-pump system, emergency heat (EM heat) is a backup heat source: electric heat strips, or a gas/oil furnace that bypasses the outdoor unit.
  • When you switch to EM heat, the outdoor heat pump is taken out of the loop and only the backup heater runs, usually at a much higher energy cost.

When you should use emergency heat

Use EM heat in true “something’s wrong” situations, not just because it’s cold:

  1. Heat pump is broken or won’t run
    • The outdoor unit won’t turn on, keeps tripping breakers, or clearly failed after a storm or power event.
 * Example: A snow‑heavy branch or falling tree hits the outdoor unit and it stops working; switch to EM heat and call for repair.
  1. Heat pump is iced over and not defrosting
    • A light frost that comes and goes is normal, but if the unit is encased in ice and never clears, you risk damage if it keeps trying to run.
 * In that case, turn off regular heat, switch to EM heat to stay warm, and schedule service.
  1. Malfunction during extreme cold
    • In very low temperatures, if the system struggles, short-cycles, or clearly can’t keep up and you suspect a fault, you can temporarily use EM heat while waiting on a technician.
  1. To protect the equipment from damage
    • During events like freezing rain where ice buildup on the outdoor fan could break fins or the motor, some co-ops and HVAC pros advise using EM heat so the outdoor unit stays off until conditions improve.

In all of these cases, EM heat is a temporary safety net, not a normal winter setting.

When you should not use emergency heat

Avoid turning on EM heat just because it feels colder outside:

  • Not for routine chilly days
    • Modern heat pumps are designed to run in cold weather and will automatically use auxiliary heat as needed without you touching the EM setting.
  • Not as a “booster” for faster heating
    • Manually switching to EM heat just to warm up the house faster usually only makes your power bill spike, since the backup heat is much less efficient.
  • Not as a long‑term setting
    • Running EM heat for days or weeks can mean very high electric bills and extra wear on the backup heater.

A quick rule of thumb: if the heat pump itself is working normally, leave EM heat off.

How long to use emergency heat

  • EM heat is meant for short-term use only , just long enough to stay safe and comfortable until the main system is repaired or thawed.
  • If you’re on EM heat for more than a day, it’s a sign you should schedule professional service as soon as possible (if you haven’t already).

Quick checklist before flipping EM heat on

Use this quick mental checklist when you’re wondering when to use emergency heat :

  • Is the outdoor heat pump clearly damaged, frozen solid, or not running at all?
  • Is the house getting cold even though the thermostat is calling for heat?
  • Have I checked that breakers are on and filters aren’t totally clogged?
  • Am I prepared for a higher energy bill for as long as EM heat is on?

If the pump is malfunctioning and the house is getting too cold, go ahead and switch to EM heat and call an HVAC pro; if the pump is just working hard because it’s very cold but still running and the house is reasonably warm, leave EM heat off.

Information gathered from public forums or data available on the internet and portrayed here.