What Does EM Heat Mean On My Thermostat?

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On your thermostat, EM heat stands for emergency heat. It is a secondary heating system backup for heat pumps in case your primary heating system fails or can’t keep up. However, many people wrongly assume they should use EM heat when the temperature drops to sub-freezing.

This isn’t true, as the system isn’t designed to function as your primary heat source. Keep reading to learn everything you need to know about EM heat.

hand switching on the emergency heat on the thermostat

What Is EM Heat?

In most cases, you use the thermostat to control the temperature throughout your entire home. However, there are a few exceptions, such as those in larger homes where multiple zoned thermostats are necessary.

When you invest in a new HVAC system (or move into a new home), it’s a good idea to familiarize yourself with the thermostat and its settings, as each one is slightly different. As you glance through the settings, you might come across a setting labeled “EM heat” if you have a heat pump.

Note: If your home has an air conditioner and furnace, you usually will not have an emergency heat setting on your thermostat.

EM heat is the setting you would engage if your heat pump can’t keep your home warm enough and prevent frozen pipes and cold toes. Since heat pumps warm your home by transferring heat from the outdoors to your home, if it’s too cold, they won’t work either.

So, on particularly cold days, emergency heat is a backup way to heat your home. Typically these emergency heat systems are electric heating coils that consumes a ton of energy. So only use it when you absolutely need to. Otherwise, you will have a gigantic power bill.

How Does It Work?

broiler room with heat pump

If your home’s heat pump needs some help warming your home, it’s usually as simple as pressing a button or flicking a switch. The switch or button will have an “EM heat” label/text, indicating the correct setting to engage.

When you turn on your home’s emergency heat, the heat pump will bypass the standard operating process and turn on the secondary heat system. To better explain this, it’s essential to understand the heat pump system.

In homes with heat pumps, there’s a two-part system: the heat pump itself and a secondary heating source. The components of your heat pump include an indoor and outdoor unit, whereas the backup heat source is inside your home’s ductwork.

The secondary heating source is a supplemental heat source when your heat pump system malfunctions or cannot extract enough heat from outside (when the temperature is too low).

Info: Homes in areas with routinely below-freezing winters usually do not have heat pumps and, therefore, no emergency heat systems. Only homes in moderate climates have whole-house heat pumps for cooling and heating.

How to Use EM Heat

The guidelines for switching to the secondary source vary depending on the heat pump and thermostat brand.

When you switch to the secondary source (or it automatically switches due to predetermined settings), your home’s compressor and heat pump will shut down completely. Once these parts shut down, your home’s electric heat strip or coils turn on.

The heating strip heats your home without taxing or damaging your outdoor heat pump system. For the most part, emergency heat is electric, but it might also run via oil or natural gas.

Note: When you manually engage the “EM heat” setting on your thermostat, you tell the system to bypass the heat pump entirely and allow direct access to the electric heat strip (or gas or oil furnace).

If you have an electric system in your home, your air handler turns into an electric furnace. There can be some variation in the specifics of how “EM heat” triggers, as some systems are set to switch if the heat pump cannot heat your home adequately. As mentioned, this can be due to failure (frozen over, faulty parts, etc.) or too-low outdoor temperatures (unable to extract heat from the air).

When Should I Use Emergency Heat?

a hand setting the thermostat’s emergency heat

You should never use emergency heat as a primary heat source. Emergency heat is not designed for long-term use and may tax your heating system. On top of that, it’s often more expensive to run emergency heat, as the electric strip is nowhere near as efficient as your heat pump.

When you use the emergency heating setting on your thermostat, your home will heat much slower than using the heat pump. The system relies on gas or electricity for continuous heat production, so your next bill after using the system will likely be much higher than usual.

Info: On average, EM Heat mode uses around 2 to 3 times the amount of electricity or gas as a heat pump.

Use emergency heat solely in emergency situations. For example, perhaps a heavy, snow-laden branch near your home snaps and lands on your heat pump. Or, maybe an ice storm whips through your area, freezing the heat pump. Or, you live in Texas and experience once-in-a-lifetime below-freezing temperatures that your heat pump can’t handle.

Either way, the heat pump might be unable to keep your home warm. So, to keep your house toasty, you’ll need to turn to emergency heat. However, don’t turn on emergency heat and forget about it; turn it off when the weather returns to normal. Or, if your heat pump is damaged or out of service, call your HVAC service provider to schedule an appointment.

What to do When EM Heat Doesn’t Turn Off

If EM heat won’t turn off in your home, that usually means your heat pump has an issue you need to repair. In this case, it is best to hire an HVAC contractor to fix it.

Once your HVAC technician repairs the heat pump, you can turn the secondary heating system off and re-engage the heat pump. If your HVAC service provider cannot service your heat pump within the next day or two, ask for recommendations regarding your emergency heat. In some cases, they might tell you to leave it on the whole time, while others might advise against it, so it doesn’t hurt to check.

If you have a fireplace, we suggest firing it up along with your emergency heat to lessen the strain on the air handler and your power bill.

Use Emergency Heat Sparingly

EM heat on your thermostat stands for “emergency heat.” It is a supplemental heating source (usually electric) for homes in moderate climates that use heat pumps. As the name suggests, only use EM heat in emergencies – i.e., when your heat pump breaks down, or it is too cold outside for the heat pump to warm your home.

If your home is using emergency heat because your heat pump isn’t working, contact an HVAC technician immediately. EM heat can’t keep protecting your home from the cold forever.

About The Author

Jonathon is a mechanical engineer with over ten years of experience in the HVAC industry. He has hands-on experience with all types of HVAC systems.

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