Emergency Heat on a Heat Pump: When to Use It
Almost every heat pump thermostat has an EM HEAT setting, and most homeowners aren't sure what it does. Here is what it means and when to switch it on.
The Short Answer: Only When the Outdoor Unit Can't Run
Emergency heat shuts off the heat pump and heats your home with backup heat only. Use it only when the outdoor unit is broken, damaged or buried in ice, and call for repair. It uses far more electricity than normal heat pump operation, so it isn't meant for everyday cold weather.
Emergency Heat vs. Auxiliary Heat
| Auxiliary Heat (AUX) | Emergency Heat (EM) | |
|---|---|---|
| How it turns on | Automatically, by the thermostat | Manually, by you |
| Heat pump | Keeps running | Turned off |
| Backup heat | Helps when the heat pump needs it | Does all the heating |
| When you see it | Defrost cycles, cold mornings, big temperature increases | Only when you switch it on |
Backup heat is usually electric heat strips in the indoor air handler. On a dual-fuel system, it's your gas furnace. Seeing AUX come on now and then is normal. Seeing it on all the time is not.
When to Use Emergency Heat
- The outdoor unit stopped running or is making a grinding or banging noise
- The outdoor unit is damaged, from a fallen branch for example
- The unit is encased in ice that a normal defrost cycle doesn't clear
- A technician tells you to run on emergency heat until a repair is done
Call for service when you switch it on. Emergency heat is a temporary bridge, not a fix. Running on it for days uses a lot of electricity and the underlying problem still needs repair.
When Not to Use It
Don't switch to emergency heat just because it's cold out. Modern heat pumps keep heating well below freezing, and Willamette Valley winters rarely get cold enough to need it. The heat pump will call for auxiliary heat on its own when it needs help.
It's also normal for a heat pump to blow cooler air for a few minutes during a defrost cycle, sometimes with a little steam from the outdoor unit. That isn't a reason to switch modes.
If AUX Heat Is On All the Time
Large thermostat setbacks
Raising the temperature 5 or more degrees at once often triggers backup heat. Smaller changes let the heat pump do the work.
Low refrigerant
A leak reduces heating capacity, so backup heat makes up the difference.
Thermostat settings
Thermostats not set up for a heat pump can bring on backup heat too early.
If your heat pump is running constantly or blowing cold air, our heat pump repair team can find out why. For a no-heat situation with a gas furnace, see our furnace troubleshooting guide.
FAQs
What does emergency heat do on a heat pump?
It turns off the heat pump's outdoor unit and heats your home with backup heat only, usually electric heat strips or a gas furnace.
What is the difference between AUX heat and EM heat?
AUX heat comes on automatically to help the heat pump when it needs it. EM heat is a manual setting that shuts the heat pump off and runs backup heat by itself.
Is it bad to run emergency heat?
It won't harm the system, but it uses much more electricity than normal heat pump operation. Use it only until the outdoor unit is repaired.
Stuck on Emergency Heat?
Valley Flow repairs every major heat pump brand across Silverton, Salem, Keizer, Woodburn, Stayton and Mt. Angel, and gets you back on efficient heat fast.