What is emergency heat and when should it be used?
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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.
Before we dive into what emergency heat really means for the comfort of your home, let’s explore the concept of heat pumps. Understanding how your outdoor unit works can help you identify issues with your system and understand when emergency heat is necessary.
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 cannot create heat or cold air on their own. They transfer warmth and coolness from one place to another.
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.
Heat pump emergency heat
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 electric heat strips turn 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. For 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 your local HVAC service provider. Your heat pump may have frozen over or need repairs. We recommend getting your heat pump repaired as soon as possible before the winter weather returns and you’re stuck without proper heating.
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.
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 hour||3,000 watts||3,000 watts + 15,000 watts|
|Hours use per day||12 hours||24 hours + 12 hours|
|Number of days||7 days||7 days|
|Total kWH||252 kWH||252 kWH + 1260 kWH|
|Cost per kWH||$0.13||$0.13|
|Total cost per week||$32.76||$196.56|
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How to tell your heat pump needs repair
Regular maintenance checks on your HVAC system is an important step 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
Your heat pump doesn’t turn on
Your heat pump doesn’t heat the home
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.
Learn more about heat pumps and other types of heating systems today. Check out our complete guide to heating for more information.