When Should I Turn on My Emergency Heat?

When the mercury drops outside, it may tempt you to flip on the emergency heat to keep your house feeling toasty warm. However, you might receive a cold surprise on your heating bill if you frequently use this feature on your heating, ventilation and air conditioning (HVAC) system.

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Before switching on your home's emergency heat, learn what it is, how it works and the potential cons of using it.

What Is Emergency (EM) or Auxiliary (AUX) Heat?

Emergency heat is an alternate heating source that works as a backup if the primary system malfunctions.

Many HVAC systems featuring heat pumps have a second stage to their heating system that uses oil, natural gas or electric heating strips. Typically, you'll find an emergency heat switch on the thermostat that lets you manually override the heat pump and use the backup heat source instead.

This fail-safe allows you to keep your home warm and your family safe from the cold while you wait for a technician to repair a faulty heat pump.

When Is It Appropriate to Turn on Emergency Heat?

As the name indicates, emergency heat is meant to provide a backup heat source during short-term emergencies. When an issue, such as low refrigerant, causes the heat pump to stop working, the emergency heat usually still works because it runs independently of the primary heat source.

If you find the emergency heat isn't working, you may need to call a technician to diagnose and repair the issue. You can easily complete some emergency heat troubleshooting steps, such as replacing dirty filters and opening vents to improve airflow.

However, issues with the HVAC system's motor or fan affect the entire system and require professional assistance. If you hear unusual sounds, such as rattling, grinding or squealing, it's best to turn off the HVAC system and call for help.

Emergency Heating Vs. Auxiliary Heating

Emergency heat and auxiliary heat both use the HVAC's secondary heating method to function. The main difference is emergency heat acts as a manual override of the primary system. You turn it on using the emergency heat switch located on or near the thermostat. You'll see an emergency heat symbol appear on the display once it's activated. Once the heat pump is repaired, you'll need to manually turn off the switch to resume normal HVAC function.

In contrast, auxiliary heat works in tandem with the heat pump and doesn't require you to flip a switch or change the thermostat setting. Your HVAC system's programming automatically turns the primary and secondary heat sources on and off as needed. For example, heat pumps regularly run a defrost cycle to safeguard against freezing. During these cycles, the HVAC automatically switches to the alternative heat source to keep your home warm.

While a heat pump offers an energy-efficient and cost-effective means of heating your home, it heats at a slower rate than other types of systems, particularly during extremely cold conditions. So when the temperature in your home is 3 degrees or more below the setting on the thermostat, the system automatically switches to the secondary heat source to speed up the heating process. It also switches over when outside conditions are cold enough to affect the heat pump's ability to warm your home sufficiently.

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Are There Any Cons of Turning on the Emergency Heat?

A heat pump draws warmth from the outdoor air and distributes it throughout the rooms in your home. Since it's transferring heat instead of creating it, the system is highly energy-efficient, especially during milder weather.

Emergency heat utilizes your HVAC system's auxiliary heat source, so running it is likely to raise your utility bills, especially if it's equipped with electric heating strips as the backup. How much it affects your bills depends on utility rates in your area and how often you use it.

Emergency heat is designed to serve as a supplement to your HVAC's primary heating source. If you're frequently using it to keep your home warm, your heat pump may need professional attention. Also, running the emergency heat continuously may put unnecessary strain on the HVAC system, leading to component breakdowns.

To safeguard against higher heating bills or extra repair costs, use the emergency heat only when necessary, and consider investing in an HVAC maintenance program. Scheduling regular system checks and filter changes can help ensure your heating system functions properly and efficiently.