What is EM heat? Everything You Should Know About Emergency Heat

If you have a heat pump system, you might have noticed an “emergency heat” or “EM heat” setting on your thermostat. The two terms are synonymous; “EM” is short for “emergency.” But what is emergency heat, and when should you use it?

Not all heat pump systems have emergency heat. EM heat is an additional feature that might not have been installed with your system. Houses in warm climates that predominantly use heat pumps for cooling don’t often include emergency heat. If you live in an area that experiences cold winters, however, emergency heat is essential if your heat pump breaks down or can’t keep up during freezing temperatures.

Not all heat pump systems have backup systems. Heat pumps in cold climates are more likely to have supplemental heating, such as electric heat strips in the air handler, a furnace, or a hot water system. Emergency heat is practical in areas where temperatures regularly drop below 35 degrees Fahrenheit. Emergency heat might not be necessary for regions with moderate climates.

The electric heat pump and the compressor shut down when the thermostat turns on EM heat. The backup system generates the home’s heat until the emergency setting is turned off. Backup systems are generally less efficient, so EM heat is only for emergencies.

A heat pump switches to emergency heat when the setting is manually selected on the thermostat and runs until it’s manually turned off. The emergency heating system can run indefinitely, but your energy bills will likely increase. Emergency heat is intended for emergencies.

The emergency heat setting should be turned on when:

• The heat pump is inoperable or unable to provide sufficient heat

• The outside temperatures are below freezing or lower than the safe operating range of your heat pump

• An ice storm occurs to avoid damage to the heat pump’s coil

No, auxiliary heat (aux heat) is different from emergency heat. Auxiliary heat is automatically activated when the heat pump can’t keep up due to low outside temperatures. The backup heating system, typically electric heat strips in the air handler, turns on and operates with the heat pump to deliver heat.

Auxiliary heat might trigger when:

• the outside temperature drops below the threshold

• the house is two to three degrees colder than the thermostat setting

• the heat pump’s defrost cycle begins  

Auxiliary heat is unnecessary for a heat pump to work in winter, but it’s a standard upgrade for houses in cold climates. Examining your thermostat for an “aux heat” light or display can tell you if you have auxiliary heat. You have auxiliary heat if your air handler contains electric heat strips or your house has another backup heating system.

Under normal conditions, set your thermostat to “heat.” This is the standard mode for heating your home with the heat pump as the primary heating system. Your heat pump system will automatically switch to auxiliary heat if necessary.

Use the “EM heat” setting when an emergency prevents your heat pump from warming your home or protects your heat pump from extreme conditions. The emergency heat setting is appropriate if your heat pump breaks down, fails to warm the house during cold weather, the outside temperatures are below freezing or lower than the safe operating range of your heat pump, and during an ice storm.

Emergency heat systems consume more energy and yield higher energy bills than heat pump systems. How much more is contingent on several factors. Different types of heat pumps and backup systems consume distinct amounts of energy. The duration, outside temperature, and energy prices further influence energy costs.

According to Home Inspection Insider, operating a heat pump in thirty-degree temperatures for one week costs about $32.76. Utilizing emergency heat strips in ten-degree temperatures for one week costs about $196.56. In this situation, emergency heating costs $163.80 more.

On the other hand, a dual fuel heat pump that uses a gas furnace for emergency heat might have energy costs equivalent to regular operation because furnaces are more efficient heaters, and natural gas prices are typically lower than electricity.  

Emergency heat or EM heat is supplemental heating used if the heat pump breaks down, can’t keep up during extremely cold conditions, or protects the heat pump’s coil during ice storms. Emergency heat must be manually switched on at the thermostat. The heat pump system is bypassed when emergency heat is initiated, and the supplemental heating system exclusively generates the home’s heat. Typically, electric resistance coils or heat strips installed in the air handler provide emergency heat, but furnaces and other heating systems can be used as well. The emergency heating system will generate the home’s heat until it is switched off.

Auxiliary heat uses a supplemental heating system but functions differently from emergency heat. Auxiliary heat is an automatic function that activates when the outside temperature drops below the threshold, the house is two to three degrees colder than the thermostat setting, or the heat pump goes into defrost mode. The heat pump continues to operate with the supplemental system providing additional heat.

Supplemental heat is an essential addition for heat pumps in cold climates. Because backup heating systems are typically less efficient than heat pumps, EM heat should be reserved for emergencies.