What is emergency heat and when should it be used?

HVAC Logo IconBy Tom MoorJuly 31, 2023
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Does your home feel chillier than normal, even with your thickest sweater on? Check your thermostat. If the temperature is significantly lower than it should be, it may be time to turn on your emergency heat.

What does the emergency heat setting do? Emergency heat is ideal for when the outside temperature is too cold for your heat pump to keep your home warm. If the heat pump freezes over or becomes damaged, then you should switch to emergency heat and call an HVAC service provider.

Schedule an appointment with a local heating expert.

What is a heat pump?

A heat pump warms your home as it pulls in heat from the outdoors, but it can also cool your home by expelling heat outside. Heat pumps use electricity and refrigerant to create a comfortable home temperature. Refrigerant transfers heat from one place to another by flowing back and forth from an indoor unit (air handler) to a heat pump compressor (outdoor unit).

If you live in an area with milder temperatures, heat pumps are great for saving money and energy. However, you should always have a backup heating source for when temperatures drop too low and emergency heat becomes a necessity.

What is emergency heat on your thermostat?

When the weather gets too cold, your heat pump isn’t able to pull enough warmth from the outdoor air to heat your home to the desired temperature. A secondary heating source, like emergency heat, can be used to keep you warm.

The heat pump emergency heat setting is used when your heat pump needs a break to avoid system damage. Plus, it works well at warming your home in below-freezing temperatures.

The “em heat” setting on your thermostat indicates your emergency heat has been activated. Emergency heat mode will continue to run until you manually turn it off.

How does emergency heat work?

When emergency heat is turned on, your compressor and heat pump shut down entirely, and your system’s backup heating system turns on. This brings in heat without damaging your outdoor heat pump system.

In most cases, emergency heat is electric, but it can also run on natural gas or oil. When you manually set the emergency heat on your thermostat, your system bypasses the heat pump and directly accesses either the electric heat strip or the gas or oil furnace. With electric systems, your air handler turns into an electric furnace.

If the temperature outside climbs to 40 degrees or above and your home still won’t stay warm without using emergency heat, call an HVAC service provider. Your heat pump may have frozen over or need repairs.

Schedule an appointment to repair your heat pump now.

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When to use emergency heat

Emergency heat should only be used in emergency situations, like your heat pump breaking down or icing over.

For example, if a snow-heavy branch snaps and crashes into your heat pump, use emergency heat while you wait for repairs. If your heat pump shorts out during an ice storm, go ahead and turn on your emergency heat. Then call for an HVAC service provider to restore your equipment and get back to a normal heating cycle.

Emergency heat should not be used for long periods of time. Emergency heat can be taxing on your heating system. By removing the heat pump from the equation, your system is solely relying on your secondary heating response. This puts a lot of strain on your backup heating element.

For all-electric systems, emergency heat should keep you warm until your heat pump can be fixed or thaws. Once your system has been mended, turn off your emergency heat to stop the increased heating rate on your electricity bill. Gas and oil furnace second-stage systems can last longer in emergency heat mode without putting too much of a strain on your home heating system.

Em heat vs. aux heat

You see both functions on your thermostat, but what’s the difference between “aux heat” and “em heat”? The answer lies in the weather and your heat pump’s condition.

Auxiliary heating is an automated function that turns on when the outdoor temperature takes a quick dip. Aux heat kicks in when the heat pump is working but there’s a difference (typically 2 – 3 degrees) between your thermostat setting and the actual indoor temperature. This supplemental heating typically only runs for up to a couple of hours. When auxiliary heat is activated, your heat pump energizes a heat strip within its system for an added heating boost. If your heat pump freezes, the auxiliary heat also becomes ineffective.

Emergency heat requires a manual switch and may need to run for hours or days, depending on your repair schedule. This secondary heating source does not work with your heat pump. As the name suggests, this function should be used in an emergency situation, and your heat pump should be shut off.

Why does emergency heat cost more?

You’ll stay warm, but the emergency heat mode can dramatically elevate your electricity bill. This type of heating uses a lot of energy and power, which means spending more money than you normally would if your heat pump was working properly.

Home Inspection Insider provides a cost breakdown comparing the use of a heat pump to combat cold weather versus emergency heat. As you can see, emergency heat dramatically increases your electric bill.

 Normal heat pump at 
30 degrees for 1 week
Emergency heat at 
10 degrees for 1 week
Watts per hour3,000 watts3,000 watts + 15,000 watts
Hours use per day12 hours24 hours + 12 hours
Number of days7 days7 days
Total kWH252 kWH252 kWH + 1260 kWH
Cost per kWH$0.13$0.13
Total cost per week$32.76$196.56

How to tell your heat pump needs repair

Regular maintenance checks on your HVAC system are important to maintaining a comfortable home. If your heat pump suddenly breaks, you may be stuck running emergency heat for a few days as you wait on an HVAC service person.

There are a few DIY fixes that can save you money upfront, but keeping to a regular maintenance schedule will ultimately save you from future frustration. For safety, most repairs should be completed by a professional heat pump repair technician.

Scroll through the list below to see if your heat pump problem is identified. If not, explore our common heat pump problems guide for more solutions.

Your heat pump runs without warming
A continuously running heat pump is normal as long as it is keeping your home warm. If the unit runs continuously but is unable to keep up with the desired temperature, call an HVAC professional. Re-check the settings on your thermostat. Does the heat pump’s air filter need to be cleaned or replaced? If not, your compressor contactor may be broken.
Your heat pump doesn’t turn on
Verify your heat pump is receiving power. Is your thermostat set to heat or did it get accidentally changed to another setting? If neither of those suggestions helps, your heat pump capacitor may be broken.
Your heat pump doesn’t heat the home
If you’ve recently had a winter storm, make sure your unit isn’t blocked by snow, ice, or fallen shrubbery. It could also be time to change or clean your air filter. If your filter and heat pump are free of debris, the issue could be with your reversing valve or low refrigerant levels. Do not attempt to refill or recharge your refrigerant on your own. This should be done by an EPA-certified HVAC professional for your safety.

Book a consultation with a heat pump technician.

Your heating emergency won’t last forever

It can be stressful when the outside temperatures begin to plummet and your heating system isn’t effectively warming your home. When needed, emergency heat is available and ready to be activated.

If your auxiliary heat hasn’t automatically turned on to warm your home, switch your thermostat to the “em heat” setting. Your home should heat up soon, and you should make a call to your local HVAC expert to inspect the heat pump. Your emergency heat should keep you and your family warm until they can arrive to fix any issues.

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Emergency heat FAQs

How do you turn off emergency heat?
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