When Does a Heat Pump Switch to Emergency Heat?

A heat pump will keep your home comfortable year-round; however, on occasion, it may switch into emergency, or auxiliary, heat. So, when does a heat pump switch to emergency heat?

This is a last resort option that kicks in if your heat pump isn’t keeping your home warm. Let's take a look at the factors that cause this back-up heat source to switch on and when to hire a heat pump professional.

What Is Emergency Heat?

You may see a setting for “EM heat” on your thermostat. This is the setting controlling your home’s auxiliary heating system. If you have this setting, you likely have a gas, oil, or electric heating system in addition to your heat pump. In colder climates, heat pumps need a secondary source of heat when temperatures drop too low for the heat pump to run at its most efficient. 

Your heater taps into this setting when outside temperatures drop too low for it to handle.

Emergency heat isn’t meant to be a primary source of heat in your home. It’s less efficient than the heat pump and will cause your utility bills to soar.

Factors That Cause a Heat Pump to Switch to Emergency Heat

Your heat pump may switch to a supplemental heat system under the following circumstances: 

Outdated Unit

A less efficient heat pump may switch to auxiliary heat because it can’t pull enough energy from the outdoor air to heat your home. This failure may occur in an older heat pump or in colder-than normal temperatures. Heat pumps have an average lifespan of 10 to 15 years, but they can extend to 25 years with proper maintenance. If your unit is on the older side of this timeline, it may be time to replace it.

Frozen Heat Pump 

If the heat pump’s outdoor unit has frozen, it may switch to emergency heat. A frozen pump will enter a defrost cycle to melt ice that has accumulated on it. During that time, it can’t heat your home. To prevent temperatures inside from dropping, the emergency heat system switches on until the defrost cycle is complete.

Unit Needs Repair

When a heat pump malfunctions or a component fails within it—for example, when it’s not blowing hot air or its fan is not spinning—the pump will switch to emergency heat. This fail-safe ensures that your home continues to receive heat until the issue is properly addressed. 

Manual Activation 

You can activate the emergency heat setting from your thermostat. This method can be used in situations when the automated system is not working to heat your home. For example, if there’s a mechanical failure that the heat pump’s sensors can’t detect. You should avoid manually activating the emergency heat feature unless it’s absolutely necessary.

How to Stop a Heat Pump from Switching to Emergency Heat

To keep auxiliary heat from switching on unnecessarily, the best defense is a good offense. Schedule preventative maintenance appointments for your heat pump system every six months with an heat pump service provider near you. 

You can check the system on your own between appointments. Make sure to keep ducts, heat vents, and areas around the outdoor HVAC unit free of debris and clutter. Clean or replace the heat pump filter each month or every other month. It’s best to call in a professional as soon as possible if you notice any issues with your pump.