What Is Emergency Heat or EM on your Thermostat? (IMPORTANT Knowledge!)

Have you ever noticed a setting on your thermostat labeled “EM heat” or “E-Heat”? If you have no idea what that is, you’re not alone.

In cold regions, heating system thermostats have a special setting called Emergency Heat, which helps your home stay warm when it’s too cold outside. It means that a backup system is activated to produce more heat.


That said, you don’t want to turn on your EM heat without first understanding what it does to your heating system and how it works.

In this article, we closely answer the question, “What is Emergency Heat?” We take an in-depth look into how EM heat works and how to tell if it’s turned on. We also provide you with reasons why you shouldn’t turn on EM heat unless absolutely necessary, so be sure to stick around!

What Is Emergency Heat or EM?

Emergency Heat, often shortened to EM heat, is a backup setting that supplements your home’s heating system with heat during freezing temperatures. That’s why it’s also known as supplemental heat.

In regions where temperatures regularly drop below 35°F, Emergency Heat automatically turns on to help a heating system work effectively. 

Most HVAC systems use heat pumps as their primary heat source and have secondary heating systems, such as gas, oil, electric, or hot-water systems.

When the outside air becomes too cold, Emergency Heat switches on and off automatically for brief periods of time to supplement the heat pumps with heat.

It’s worth mentioning that not all HVAC systems include an Emergency Heat setting. If you live in an area where temperatures rarely fall below 40°F, your HVAC system is unlikely to have this setting.

How Does Emergency Heat Work

In colder climates, HVAC systems are typically composed of two components: heat pumps and a backup heating source.

Heat pumps derive their heat from outside air, but when the air temperature drops below a certain threshold, these pumps can’t transfer enough heat to warm your home. In that case, the EM heat setting automatically turns on the backup source until your interior is warm enough.

It cycles on and off to maintain the desired temperatures or until the heat pumps can provide enough warmth on their own.

Some thermostats don’t have the emergency heat function.

However, if an issue occurs with the heat pumps, Emergency Heat switches on and your system relies completely on the backup source of heat.

You can also manually activate Emergency Heat, instructing your HVAC system to stop using the primary heating source and rely solely on the backup source.

How to Know If Emergency Heat Is On

When Emergency Heat is on, a red indicator light goes on. This red light means that your HVAC system is running in emergency mode.

If you haven’t turned on the EM heat and there are no obvious problems with your heating system, you should call a technician as soon as possible to avoid wasting energy.

There’s no need to panic if you discover that your EM heat has been accidentally turned on. The switch used to activate it is also used to deactivate it.

Why You Shouldn’t Use Emergency Heat

Many people mistakenly believe that switching to Emergency Heat improves the performance of their furnaces or heat pumps in extremely cold weather.

However, as the name implies, Emergency Heat should be used only in an emergency such as extremely cold weather.

Here are some reasons why you should avoid using Emergency Heat at all costs:

Astronomical Energy Bills

Because Emergency Heat consumes far more energy than primary heating, it’ll raise your electricity bill significantly.

When you activate EM heat, the source of your heat shifts from the heat pump to the electric heat strip, which is significantly less efficient and thus more costly.

It’s difficult to predict how much your electricity bill will rise if your backup system runs on gas or oil. You’ll need to consider fuel costs as well as system efficiency.

However, if your heating system is entirely electrical, Emergency Heat will undoubtedly be more expensive.

Turning on the EM heat will typically increase your bill by two to three times. If you have a large house and the temperature outside is extremely low, your bill may skyrocket.

While energy bills will vary depending on your heat pump’s backup system, one thing is certain: turning on Emergency Heat will ramp up your bills.

Wearing Down Your System

Using Emergency Heat as your main source of heat can damage your heating unit.

When you switch on EM heat, it consumes energy from backup gas, oil, electric heat strip, or electricity to heat your home.

This complete reliance on your system’s backup element places an undue strain on it, which should only be done for short periods of time.

The more time passes with Emergency Heat turned on, the more damage the entire HVAC system may sustain. That’s why it’s crucial to have a qualified technician inspect and repair any problems as soon as possible.

When Can You Use Emergency Heat

Emergency Heat is a backup setting, so you should only use it when your primary heat isn’t functional. You’ll almost never have to activate Emergency Heat yourself.

When temperatures fall below a certain threshold, the heating system will automatically activate to supplement your primary heating system.

Aside from that, the only time you should manually activate Emergency Heat is if your primary heating source is broken. This should only be a temporary situation, though!

If your heat pumps aren’t defrosting or your heating system isn’t keeping your home warm, you can use EM heat until a qualified technician can come and fix the problem.

What is auxiliary heat?

Auxiliary heat is an additional source of heat in your home, which can be switched on in addition to your primary heating system. It offers you a way to increase the warmth of your home and make it more comfortable when the outdoor temperature drops.

Auxiliary heating is commonly used in areas that experience harsh winters but where the primary residence isn’t equipped with a suitable heating system. In such circumstances, auxiliary heaters are installed as a backup source of warmth when outdoor temperatures dip below what is considered comfortable.

To monitor this, we can take a look at our thermostat. There should be a light that indicates whether the auxiliary heat is active or not. Not everyone has two different heating systems so if you live in a warmer climate, you won’t see this system kicking in. A plumber should do the regular maintenance of your heating system if you have this type of heating activated.

The main difference with emergency heat is that auxiliary heat can turn on by itself. Emergency heat has to be activated. This is mainly because the latter uses more energy and causes more wear and tear for your systems.

In Conclusion

Many homeowners ask the same question when they first come across their heating system’s thermostat, “What is emergency heat?”

Because EM heat usually turns on and off automatically, there are very few occasions when you have to use it.

Still, it’s an essential function that you should know what it does so that you’re ready to use it when the time comes.

Just make sure you don’t accidentally turn on the EM heat to avoid receiving a large bill. When you do use it, make sure not to use it for too long and that you get a professional to fix the heat pump problem as soon as possible.

It is important that you let your furnace be checked regularly to avoid issues during winter. Plumbers have special procedures to maintain your system.

We have discussed here what to do when your thermostat is on but the heating system is not working.