Do All Heat Pumps Have Emergency Heat?

If you walk by your digital thermostat during the cold winter months, you might have noticed the words “Aux Heat” flashing on the read-out. You might be wondering what it means and if all heat pumps have emergency heat.

All heat pumps in the northern climate (below 35 degrees) have a backup heating system known as emergency heat or auxiliary heat. When the indoor temperature reaches 2-3 degrees colder than the set indoor climate, your thermostat energizes auxiliary heat to compensate for the temperature drop.

What is Emergency Heat?

Emergency heat is often referred to as auxiliary heat, backup heat, or even heat strips. Emergency heat (EM) is a “standby” secondary heat on a heat pump. It is designed purposely to protect you from extreme cold weather when the heat pump’s primary heat solution is overwhelmed or unavailable for whatever reasons.

Heat Aux heat, or auxiliary heat, is a component of emergency heat, but they are not the same thing. Auxiliary heat will kick on automatically to work with the heat pump. Heat pumps work by using heat transfer from warmer outside air blowing across the outside condensing coil

 Heat pumps cannot create heat or cold air on their own. Most heat pumps use electric heaters for emergency heating. With an electric system, this will turn the air handler into an electric furnace by using a set of radiant heat strips.

The electric furnace is integrated into the heat pump system such that it automatically takes over when the unit is overwhelmed. Typically, the secondary heat source is activated when outdoor temperatures drop below 30°F to 40°F. However, you can also turn on the emergency heat mode manually.

For instance, if your heat pump is broken or not giving off enough heat, perhaps due to low refrigerant, a backup heat source can step in until you fix the primary heat source.

These supplemental heating sources are things such as the electric resistance heating at the indoor unit, gas, oil, or even hot-water backup systems. The supplemental heat will continue to provide heat when the outside temperature is too cold for the heat pump to work effectively

Do All Heat Pumps Have Emergency/Aux Heat?

All heat pumps in the northern climate (below 35 degrees) have a backup heating system known as emergency heat or auxiliary heat. When the indoor temperature reaches 2-3 degrees colder than the set indoor climate, your thermostat energizes auxiliary heat to compensate for the temperature drop.

However, a few models lack the valuable setting. For instance, the Payne Model PF1MNC030000 doesn’t have an auxiliary heat function. Whether or not a heat pump has an emergency heat component depends on many factors, including the heat pump model and when it was made.

Typically, older heating units don’t have the EM component as the technology was developed many years after the discovery of heat pumps.

Similarly, many units on the cheaper end often lack the feature, perhaps because of the costs involved in integrating the technology into the heat pump. This means you have to shop more carefully if you want a unit with the EM component.

How Do I Know if My Heat Pump Has Emergency Heat?

There are several ways to know whether your heat pump has a auxilliary heat. the following are a few to consider;

  • Check for an emergency heat switch: If your heat pump has emergency heat, it will almost certainly have an “EM,” “E-Heat” or emergency setting on the thermostat, complete with an emergency heat light.  
  • Check your owner’s guide: If you can’t locate the EM switch, refer to your owner’s manual. It will most likely tell you whether the appliance has the setting, where to find it, and even how to use it.
  • Call the seller or manufacturer: Many sellers know all models with auxiliary heat. However, you can also call the manufacturer directly. They’ll be happy to help.
  • Lookout for signs of EM heating: For instance, if your heat pump keeps running even when outdoor temperatures drop below 30 degrees, you almost certainly have auxiliary heat. You’ll also know you have EM heat if the heat pump’s outdoor unit is off but heating goes on as usual inside the house. The indoor unit has the backup heat and together with the thermostat, they decide when to kick in the aux heating system.

The AUX is an ‘ indicator’ on your thermostat that you are running the heat strips when the switch is set to heat. The outdoor unit is where the heat pump is located and the indoor unit is either a gas furnace or air handler.

Auxiliary heat uses electric resistance heating, which is much less efficient than your heat pump. Therefore, a heating system stuck in AUX heat will run up an energy bill.  If your thermostat stays in “Aux Heat” even when the temperatures outside rise, you should call to have it serviced

Does a Heat Pump Automatically Switch Emergency Heat?

Yes, EM heat activates automatically under normal circumstances. The feature is wired to the rest of the heat pump’s control system such that the heating load is automatically transferred to the electric heat strip when the primary heating system is overwhelmed.

Sensors inside the heat pump monitor the primary heat source and alert the control panel when temperatures drop below 30°F.

Then the circuit board shuts down the primary heat source and activates the electric heat strips. However, this only applies when the heat pump is overwhelmed but working. You need to manually turn ON emergency heat if the heat pump breaks down.

At What Temperature does Emergency Heat Turn ON?

The majority of heating pumps activate the electric heat strips when outdoor temperatures drop below 30 degrees Fahrenheit. However, it’s not a fixed number. For instance, many heating pumps activate emergency heating when outdoor temperatures drop below 40°F. It depends on the heat pump model.

The reason is that they begin to struggle when outdoor temperatures drop so low. At 40°F or lower, the heat pump can no longer extract enough heat from outdoor air to keep your rooms at 68°F to 72°F, i.e., the DOE’s recommended thermostat setting for winter. It can try, but it puts a lot of weight on the appliance, which can result in internal damage.

Moreover, heat pumps frosting/freezing during winter is a major concern at such low temperatures as removing heat from already very cold air easily causes freezing. That’s why you get a lot of frost and ice around the outside unit on particularly cold days.

It’s nice that these units have a defrost feature to remove the ice to keep the heat pump running. However, you may easily find your heat pump in a permanent defrost mode when temperatures drop too low. Therefore, it makes more sense to switch to emergency heat at this point.

Should I Switch my Heat Pump to Emergency Heat?

Yes, you can switch your heat pump to emergency heat when needed. However, you shouldn’t, unless it’s necessary. The first reason is that they automatically switch to auxiliary heat when needed.

As we’ve seen, the heat pump’s controls will switch to EM heat without your intervention if temperatures drop below 30°F or 40°F, depending on your heat pump type. Therefore, you don’t have to turn it on manually.

Secondly, EM heat is very expensive. It costs about six times more to heat with EM heat than regular heat pump heating. This means you should use EM heat only when you have no other options. More importantly, you want to use it for the shortest time possible.

However, this doesn’t mean you can’t manually switch ON emergency heat altogether. For instance, you’re allowed to turn on emergency heating if the heat pump is broken or if it won’t respond.

You can also manually switch it on if the automatic switching doesn’t happen even after outdoor temperatures drop below 30°F. 

How do you know if the Emergency Heat Setting is ON?

When the EM heat setting is on, there will be a red indicator light and may also have a symbol on the thermostat display. If you see the emergency heat indicator on when you did not trigger the EM heat setting, then you could use extra energy for no benefit.

How to Turn ON Emergency Heat

How to turn on emergency heat on a heat pump depends on the heat pump. So, it’s not easy to provide the exact steps for all heat pumps.

However, the general procedure is as follows;

  1. Confirm that your outdoor unit is not producing heat, or if it’s producing very little heat, turn it off first.
  2. Head to your thermostat (or heat pump control panel)
  3. Locate the emergency heat setting on your thermostat. It’s usually marked “EM,” “Emergency,” or “E-Heat
  4. Slide or press the switch to turn ON the EM heat setting
  5. Verify that emergency heat is ON by confirming whether you’re now getting heat in your rooms.

The process is a little different when using Nest thermostats. The following is a step-by-step guide to follow;

  1. Connect your emergency heating wire to the star (*) connector on the thermostat
  2. Go to your thermostat and select “Settings” from the “Menu”
  3. Select “Equipment”
  4. Click “Emer. Heat”
  5. Confirm that you want to switch on emergency heat
  6. Define the desired heating set point In both cases, make sure to call your HVAC services provider to troubleshoot the outside unit as soon as the emergency heat is on. You don’t want to heat with the EM feature for too long as it’s very expensive and puts too much strain on the heat pump.

When Should you Use Emergency Heat?

You should only use emergency heat if first-stage heating isn’t working to the required level or not working at all. This means you should only use emergency heating on two occasions;

  • First-stage heater is broken: You’re free to manually turn on the emergency heating component if it’s winter and the first-stage heating component isn’t working.
  • First-stage heater is overwhelmed: You’re also at liberty to activate EM heat if the outdoor unit seems overwhelmed and the unit hasn’t automatically switched to EM heat.

Is Emergency Heat Expensive to Run?

Unfortunately, yes. Emergency heating can leave you with a massive electricity bill. Although the statistics are hard to come by, some figures show that it costs up to six times more to run EM heat than first stage heating with a normal heat pump.

It is understandable given that heating pumps are some of the most cost-effective space heaters today as they merely transfer energy from one point to the next.

Meanwhile, EM heaters are often electric resistance heating systems, which are some of the most expensive heating solutions today. Even gas and oil-powered EM heaters are still multiple times more expensive than first-stage heat pump heating.

It’s the main reason we strongly warn against running emergency heat for a long period. If your primary heater is broken and EM is your only option, then fine. However, if you have other options or can fix the first-stage heater quickly, then EM heat should only be a very short-term solution.

Do All Heat Pumps Have Emergency Heat? FAQs

How does Emergency Heat Work?

Emergency heat refers to second-stage heating in heat pumps that activate when the first-stage heating system is broken or overwhelmed. Most EM heat systems are electric-powered, while others are oil and natural gas-powered.

What Happens if I Accidentally Turn ON Emergency Heat?

If you have accidentally activated your EM switch, don’t panic. It’s not dangerous in any way but leaving your thermostat on emergency heat forces your heat pump to use this option no matter what the outside temperature. Moreover, you can easily deactivate it. Simply locate the EM switch on your thermostat and turn it off.

How much more Expensive is Emergency Heat?

It’s not easy to tell because the data is very hard to come by. However, a few people who’ve compared the figures say that electric resistance heating is up to six times more expensive than first-stage heating.


The big takeaway here is that not all heating pumps have an emergency heating (EM) feature. Most modern units do. However, many older units don’t.

That said, though, you should strongly consider heat pumps with EM heat when shopping as the feature can prove invaluable when your heat pump is broken or overwhelmed.