Emergency heat is a backup mode on a heat‑pump system that turns off the outdoor unit and uses a secondary heat source (like electric heat strips or a gas/oil furnace) to keep the house warm when the main heat pump can’t or shouldn’t run.

What “Emergency Heat” Actually Does

When you flip the thermostat to EM HEAT (or when the system switches to backup heat in some setups), this happens behind the scenes:

  • The outdoor heat pump/compressor is shut off so it stops trying to pull heat from outside air.
  • The system “bypasses” the heat pump and goes straight to the backup heat source (electric strips, gas furnace, or oil furnace).
  • The air handler (indoor unit) effectively acts like an electric or gas furnace, directly generating heat instead of moving it from outside.
  • Heat runs continuously from the backup source until you turn emergency heat off on the thermostat.

In simple terms: instead of transferring heat (efficient), emergency heat creates heat (less efficient but reliable).

Emergency Heat vs Auxiliary Heat

People often see both “Aux Heat” and “EM Heat” and wonder if they’re different systems.

  • Auxiliary heat :
    • Automatically kicks on when the heat pump needs help—like when it’s very cold (often around 25°F or below) or the house needs to warm up quickly.
* The heat pump still runs; the backup heat just adds extra warmth.
  • Emergency heat :
    • You manually switch it on at the thermostat.
    • The system shuts down the heat pump and uses only the backup heat source.
* Stays on until you turn it off again.

A handy way to think of it:
Aux heat = “Assist me.”
Emergency heat = “Forget the pump, use backup only.”

When You’re Supposed to Use Emergency Heat

Emergency heat is named that way on purpose—it’s not meant for everyday use.

Common legit reasons to use it:

  1. Heat pump failure or damage
    • Outdoor unit isn’t running, is visibly damaged, or is iced over and not defrosting.
    • EM Heat keeps the house warm while you wait for a technician.
  1. Severe malfunction in very cold weather
    • House is not heating, the heat pump is struggling, making bad noises, or short cycling.
    • You can switch to EM Heat to protect the equipment until it’s checked.
  1. Thermostat says “Emergency Heat” by itself
    • Some systems show this message if the main heat source isn’t functioning correctly and they have switched to backup.
 * That’s your cue to call for service, not just ignore it.

If your house is warm and the system seems fine, you usually do not need to manually turn on emergency heat.

Why Emergency Heat Is So Expensive

Emergency heat often relies on electric resistance heat (like giant toaster coils in your air handler). These are simple but power‑hungry.

  • Heat pumps move heat, which is very efficient.
  • Electric strips create heat, which uses a lot more electricity for the same warmth.
  • Running EM Heat for long periods typically produces much higher utility bills , especially if your backup is electric.

If your backup is gas or oil, it may still cost more per hour than normal heat‑pump operation, but the exact cost difference depends on local energy prices.

How It Fits Into Today’s Context

In recent winters, a lot of homeowners have posted questions and forum threads about huge power bills after cold snaps—often because they unknowingly left EM Heat on for days. With energy prices and home efficiency now trending topics, understanding emergency heat is part of “HVAC literacy” people are trying to build so they don’t get bill shock in January.

Many modern thermostats are designed to manage auxiliary heat automatically, so most people hardly ever need to touch the EM Heat setting at all.

Mini FAQ: Quick Answers

  • Does emergency heat make the house warmer than normal heat?
    Not really. It can feel warmer faster in some cases, but the main difference is cost and how the system is operating, not maximum temperature.
  • Is it bad to run emergency heat all winter?
    It won’t usually “break” the backup heater, but it’s not what the system was designed for and your bills can skyrocket. It also means your heat pump is not doing its job and probably needs service.
  • If it’s just really cold outside, should I flip to EM Heat myself?
    Usually no. Modern thermostats and heat pumps automatically decide when to add auxiliary heat. Manually forcing EM Heat is mainly for when the heat pump is malfunctioning or unavailable.

One Simple Example

Imagine a winter storm knocks ice onto your outdoor unit, and it freezes up so badly it stops working. The house begins cooling down, and the heat pump can’t recover. You switch the thermostat to EM HEAT, which tells the system, “Ignore the outdoor unit—use the backup furnace or electric strips only.” Your home warms back up and stays comfortable while you wait for an HVAC tech to fix or defrost the heat pump.

TL;DR: Emergency heat turns off your heat pump and relies only on a backup heat source so you can stay warm when the main system can’t keep up or is broken—but it’s meant for short‑term use because it’s much less efficient and more expensive to run.

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