What Is Emergency Heat Thermostat? Everything About It

Modern thermostats feature an EM setting. The name, of course, refers to an emergency, but many homeowners wonder what the setting’s appropriate use is. So, what is the EM setting all about?

The EM setting on your thermostat controls your secondary or backup heating system. It’s designed for use when your heat pump system fails to generate heat. EM usually draws from a secondary fuel or energy-based source, like electricity or oil.

This article explains all the vital information about the EM setting, how it works, and when to use it. Once you’ve finished reading, you’ll understand when the EM setting turns on, how you can work it manually, and how to keep your home warm in any setting. You will also know how to avoid such emergencies, so let’s jump right in. 

EM Heat on Thermostat Settings: What It Is, Its Role, and When to Use It?

Your home’s heat pump is responsible for delivering heat throughout your house. It draws on the warm underground air and sends it into your home through an HVAC system. 

However, there’s a point where the temperature outdoors drops too far. At such low temperatures, the pump may be unable to make a difference, leaving you at the mercy of low temperatures. Enter EM heat. 

By activating your thermostat’s EM heat setting, your home thermostat switches from the heat pump to a secondary source to heat your home. It then stays that way for as long as the EM mode is activated. The mode is automatically activated when the temperature reaches a predetermined low, but you can also activate it manually. 

The best part about EM heat is that you don’t have to guess whether or not it’s active. Your thermostat will have a light indicating when it’s drawing on the backup heat source. You can test the system by briefly switching EM on and checking for the light.

The EM heat setting can be a lifesaver (quite literally), but you shouldn’t use it as a long-term solution to heat loss. In the case of automatic activation, it will deactivate when your heat pump is functional again. 

In addition, you should avoid turning the EM heat setting on manually as much as possible because it is an inefficient method that can drastically increase your heating bills. As the name suggests, the EM heat mode is best reserved for true emergencies. 

Read: Ecobee Thermostat’s Internal Temperature Sensor Isn’t Working. How To Fix?

When to Manually Switch on EM?

The best time to manually switch on EM is when you’re experiencing problems with your primary heating system, and you’re waiting for a specialist to come and diagnose the problem. The manual EM can get you through the wait comfortably.

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When you don’t have a timetable for a solution or if you won’t get a specialist over immediately, it’s best to leave EM off and find another way to stay warm. Emergency heat is less efficient than your primary heating system, resulting in higher bills with less warmth.

The lower efficiency also means your EM system will suffer wear faster than your primary HVAC. Running it when it isn’t necessary could cause it to harm your EM system in ways that prevent it from kicking when you actually need it. Letting the system activate automatically is the best way to get the most out of it.

Read: Why Honeywell Pro Series Thermostat Cool On Is Flashing?

Examples of Manual Emergencies

Of course, some emergencies warrant using the EM setting. One such situation is if the pump itself breaks. Repairing or replacing it will likely take time, so you can use EM in the interim to keep yourself safe and warm.

Another scenario is if your pump freezes. The automatic trigger may switch on in such a case, but the ice accumulation could stop and interfere with the pump’s ability to activate the setting. Manual activation is a good idea if the air is suddenly very cold, but the thermostat hasn’t made the switch.

You can keep costs low in two ways when you activate EM heat, and both are centered around using the setting sparingly and only when necessary.  

First, contact an HVAC specialist to have the problem with your primary system fixed as soon as possible. The longer you wait to make the call; the higher your energy bills will be.

Second, be strategic about when you rely on EM heat. Instead of keeping it on 24/7 while your primary system is offline, think about when you need the heat most and only run it during those hours

For example, you can likely find ways to stay warm during the day, so save EM heat for the night when you’re sleeping. 

Read: How To Fix Ecobee Sensors Not Matching App And Thermostat Readings?

Why is My Emergency Heat Cold?

If you switch on emergency heat and feel the cold air rushing out of the vents, it’s likely not a problem with your HVAC system. 

Remember that the secondary heating system is less efficient, so when temperatures get very low, they may not make a noticeable difference. In all likelihood, the system itself is perfectly fine and functional.

If EM isn’t making a substantial difference, you should consider switching it off to avoid wearing down the system. Otherwise, the low temperature could further stress it and cause undue harm.

Read: Ecobee Thermostat Not Reading Correctly? 

Ways To Maintain Your Heat Pump

Of course, the best way to ensure your emergency heat will be there when you need it is to take care of your heat pump. However, doing so requires a certain understanding of how the device works. So here’s a short list of problems that can inhibit emergency heat and how you can fix them.

Frozen Coils

As part of its regular operations, your heat pump utilizes evaporator coils. Its heating cycle sends refrigerant to these coils and creates condensation

In warmer conditions, this moisture drips off and runs down a drain, but it will freeze on the coils when it’s cold.

Heat pumps have a defrost feature that will safely remove small amounts of ice. However, extremely low temperatures mean ice builds up faster than the defrost function can handle. It could also mean the unit needs more refrigerant.

If you look inside the unit and see frost on the coils, you can usually remove it without much trouble. First, make sure the pump is turned off, and gently try to remove the ice buildup with your hands or warm water.

Read: Ecobee Thermostat Air Quality Problems And Solutions

Dirty Air Filter

You should regularly check and change your heating pump’s filter to prevent blockage. The debris that gathers on it over time can eventually block airflow. This buildup of dirt and grime forces the system to work harder to get the air out, straining it and thereby shortening its lifespan.

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Not Enough Refrigerant

Refrigerant runs through the heat pump in a closed-loop system and is how air moves throughout the unit into your home. 

When first installed, your pump has a fixed amount already inside, and the level doesn’t change as you use the pump. However, leaks can happen. The pump will then produce less warm air until the refrigerant leaves the system completely.

Unfortunately, this problem isn’t one you can fix on your own. The leaking component will need replacing, as will the refrigerant. You’ll need to call on a specialist to complete both tasks safely.


The EM setting on your thermostat is a backup plan should your primary heating system encounter problems and not function. 

The emergency system will, in most cases, switch on automatically when the outdoor temperature drops to a predetermined point. You can activate the emergency setting manually. However, it’s best to avoid doing so because it results in higher energy costs and will strain the system.