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When the temperatures outside dip too low, are you tempted to switch on the EM Heat setting on your Honeywell thermostat. Or perhaps you’ve just installed your heat pump and are trying to understand what the setting does. We explain all!

EM heat and heat pumps

The heat pump in your home works in 3 main modes:

Primary heat pump

In this mode, your heat pump works in the same way as your air conditioner, just that in this case, it pulls warm air from outside into your house. The moving heat mode is the main heating method in any heat pump.  

Auxiliary heating

Sometimes when the air outside is too cold, your primary heat pump isn’t able to bring in enough warm air. And that’s where the aux heat comes in.  Your HVAC system will automatically turn on your electric heat strip to generate the extra heat that you need.

Backup furnace

The cost of using electricity as the backup heat for your house can significantly add up. Thus, when the outside heat goes too low for a prolonged period, most homeowners prefer to switch to a gas furnace as their source of auxiliary heat. That’s because gas is cheaper than electricity yet equally effective.

What is emergency heat?

EM heat is the short form of emergency heat. As the name suggests, it should only be used in cases of emergency.

By switching on your Honeywell thermostat’s EM heat, you’re simply commanding your system to switch off the primary heat mode and rely only on the auxiliary mode.

Your pump will now either run solely on the electric heat strip or the backup gas furnace. Both of these modes will keep you warm and toasty. However, when using the electric heat strip as your main source of heating, your electricity bill will shoot up.

Beware of manually switching!

Sometimes, when the temperatures outside are too low, you may think that manually turning the em heat setting on will keep you warmer. But that may be a costly mistake!

Your heat pump is an automatic device. It senses when the heat levels outside are too low and in such cases, switches the auxiliary switch on to boost the warmth levels in your home. And once the heat levels outside are back to normal, your pump switches the auxiliary heat off to save on energy.

Even in the coldest winters, do not be tempted to switch on your emergency heat thinking that you’ll supplement the heat in your home. Your HVAC system is automated and will regulate the heat pump accordingly.

When should I use emergency heat?

Sometimes, when the outside heat levels are low, your primary heat pump may not generate enough heat to keep your home warm. In such cases, your HVAC system instantly turns on your auxiliary heating unit to supplement the heating needs.

On the other hand, if you turn on your emergency heat, your HVAC system completely shuts down your primary heat pump. Your system then relies only on the auxiliary heating unit, which in most cases is gas or electricity.

When you’re using the auxiliary heating unit alone, your heating costs may double (or even triple). That’s why the Honeywell thermostat EM heat is intended for use only during emergencies.

Has a tree fallen on your heat pump and it no longer works? Did your heat pump freeze out in the cold and has stopped working? That’s when you can turn on the EM heat as you wait to replace or repair your primary heat pump.

What does emergency heat do?

Emergency heat works in the same way as your primary heat pump. The only difference is that you’re only relying on the secondary heating unit of your HVAC system. This auxiliary heat can either be an electric heat strip or a backup gas furnace.

But remember, the electricity or gas heat unit is intended for use only as a secondary source of heat, for a good reason. These heating units are less efficient and also quite expensive.

Under normal circumstances, your heat pump is adequate to maintain the desired temperature in your home 24/7. And when the temperatures drop too low, the heat pump turns on the auxiliary heating unit to supplement your home’s heating needs.

Accidents or Malfunctions

But, sometimes, due to an accident or malfunction, your primary heat unit may fail. What next? You’ll have no choice but to use your backup heat unit.

As a general rule of thumb, only use your Honeywell thermostat EM heat for the shortest durations possible as you arrange to repair your heat pump. Otherwise, your utility bills will rapidly rise.

Is emergency heat more expensive to run?

Yes. Emergency heat is much more expensive to run than your primary heat pump. The extra cost will depend on your source of heat and how long you’ll use it.

The most common types of auxiliary heating units are gas furnaces and electric heat strips. And although both are reliable, the cost of running emergency heat on electricity is significantly greater than when using gas or the heat pump.

That’s why your emergency heat setting should only be used for emergencies. Contact a professional technician to ensure that your heat pump is up and running within the shortest time possible.

What an illuminated emergency heat light indicator means

Have you noticed a red light indicator on your thermostat or on your heat pump? The illuminated emergency heat light indicator means that your Honeywell thermostat EM heat is switched on. And, your HVAC system is currently relying only on your auxiliary heating unit.

If you didn’t activate the emergency mode, first confirm to ensure that someone else hasn’t activated it, either by mistake or on purpose. If it was by mistake, simply switch it off and your heat pump will continue to work as it should.


So there you have it! We’ve detailed what the Honeywell thermostat EM heat setting is, what it means, when to use, and what to do when the indicator is on.

Always remember that this is an emergency setting. And when it is used for a prolonged period, your heat bills will significantly go up. It’s also important that you keep on checking your thermostat from time to time. That way, it will be easier to notice in case the EM heat mode is switched on by mistake.


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