Emergency heat is a backup setting on heat-pump systems that turns off the outdoor heat pump and uses a secondary heat source (like electric heat strips or a gas/oil furnace) to keep your home warm when the main system can’t do the job safely or efficiently.

What Does Emergency Heat Do?

Emergency heat (often shown as “EM Heat” on the thermostat) is a manual backup mode built into heat pump systems.

When you switch to emergency heat:

  • The outdoor heat pump/compressor shuts off completely.
  • Your backup heater turns on instead (electric heat strips, gas furnace, or oil furnace, depending on your system).
  • The system stops trying to pull heat from outside air and just generates heat directly indoors.

In practical terms: it’s there to keep your house warm when the heat pump can’t keep up or is damaged, not as a “stronger heat” button for very cold days.

Quick Scoop (the basics)

  • It’s a backup heat source for heat pumps, not the primary one.
  • It bypasses the outdoor unit and runs only the indoor backup heater.
  • It’s usually much more expensive to run (especially electric strip heat).
  • You typically turn it on manually when there’s a problem with the heat pump.
  • Normal cold-weather “help” is called auxiliary heat ; emergency heat is a step beyond that.

Think of it like using a spare tire: it keeps you going, but you don’t drive on it for weeks.

How It Works (Simple Breakdown)

Normal heat pump mode

  • The heat pump pulls low-level heat from outside air and moves it indoors.
  • This is efficient and cheaper to run than electric resistance heat.

Emergency heat mode

When you flip the thermostat to EM Heat:

  1. The outdoor unit/compressor turns off completely.
  1. The system uses only the backup heater:
    • Electric resistance coils in the air handler (like a big space heater), or
    • A gas or oil furnace as backup.
  1. It keeps running in this backup mode until you manually switch it back to normal heat.

Because it’s generating heat instead of moving it, it draws a lot more energy, especially with electric strips.

When You Should Use Emergency Heat

Most pros say you should only use EM Heat in these situations:

  • The heat pump is broken or frozen
    • Outdoor unit is iced over and not defrosting, making little or no heat.
* The unit won’t turn on or is clearly malfunctioning.
  • You’re waiting on a repair
    • The technician is scheduled, but your house is getting too cold.
  • Extreme cold and no recovery
    • In some setups, if the heat pump just can’t keep up and indoor temps keep dropping, switching to EM Heat can stop the slide until conditions improve or a tech checks the system.

In all these cases, EM Heat is a short-term safety and comfort feature, not a seasonal setting.

When You Should NOT Use It

Common mistakes:

  • Turning on EM Heat just because it’s cold outside, even though the system is working.
  • Using it all winter thinking it’s “stronger” or “better” heat.
  • Flipping to EM Heat every time you see “AUX” on the thermostat (auxiliary heat is automatic backup, which is normal in very cold weather).

These habits can cause:

  • Very high electric bills (especially with electric strip heat).
  • Unnecessary wear on the backup system.

EM Heat vs Aux Heat

Here’s a clear side‑by‑side:

[9][3] [8][3] [3][9] [1][5][3] [9][3] [5][7][3] [5][3] [6][3][5] [3][9] [10][7][5]
Feature Auxiliary Heat Emergency Heat
How it turns on Automatically when heat pump can’t keep up or in defrost cycles.Manually selected on the thermostat by you.
Heat pump status Heat pump still runs; backup heat assists.Heat pump is shut off; only backup heat runs.
Purpose Help the system maintain set temperature in very cold weather or defrost.Keep home warm when the heat pump is failing, frozen, or intentionally taken offline.
Cost to run Higher than normal, but usually used intermittently.Usually the most expensive mode, especially with electric strips.
How long to use Short bursts as needed, automatically controlled.Short‑term only, until repair or conditions improve.

Real-World Example

Imagine a January cold snap:

  • Your heat pump runs constantly but the house is still dropping below your set temperature.
  • You look outside and see the unit encased in ice, not defrosting.
  • To avoid losing all heat while waiting for a tech, you manually switch the thermostat to EM Heat.
  • The outdoor unit shuts off, and the indoor electric heater or gas furnace takes over to keep the home livable until the system is fixed.

That’s exactly the scenario emergency heat is designed for.

“Latest news” & forum-style chatter

In recent homeowner guides and utility posts from late 2024–2025, there’s a noticeable push to correct myths that you should use EM Heat whenever temps dip below a certain number (like 25°F). Many modern systems instead rely on automatic auxiliary heat and efficient cold‑weather heat pump design, reserving EM Heat for actual failures or extreme cases.

On home-improvement forums, people often post things like:

“My thermostat says EM Heat—did I break something?”

The usual community answers line up with HVAC pros:

  • Check if the thermostat was bumped into EM Heat accidentally.
  • If the system switched to a backup source because the main heat pump is malfunctioning, call a technician and use EM Heat only as a temporary backup to stay warm.

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