Heating & Cooling

Heat Pumps and Emergency Heat: What You Should Know

Heat pumps are very efficient when heating a home above 30 degrees. But, even in moderate climates, you can expect some freezing nights. Heat pumps and emergency heat are designed to help keep up with demand in freezing temperatures. However, it’s important to note that emergency heat is expensive to use and shouldn’t be your primary heat source.

All heat pumps have a backup heat source known as emergency or ancillary heat. When it’s freezing, heat pumps use emergency heat to meet the thermostat’s demand.

If you increase your heat pump thermostat setting by more than 2 degrees, heat pumps switch to emergency heat. Heat pumps often use emergency heat to reach the desired temperature.

I will explain how emergency heat works and answer common questions about it. To better use the heat pump in your home, understand these explanations.

Heat Pumps and Emergency Heat: What You Should Know

The heat pump uses electric emergency heat to warm the home to the setting on the thermostat. Heat pumps engage the emergency heat when needed. You do not need to set your thermostat to emergency heat.

No matter how cold outside, your heat pump will use emergency heat if you set your thermostat to it. Emergency heat, also called ancillary heat, costs more because it needs extra electricity for the heating coil.

The table below shows the costs of using a normal heat pump in 30 degrees F weather for one week. It also compares the costs of using the heat pump in 10 degrees F weather with the emergency heat for 12 hours a day.

Cost BreakdownNormal Operation
at 30 Degrees
for 1 week
Emergency Heat
Operation at 10
Degrees for 1 week
Watts per hour:3000 watts3000 watts + 15000 watts
Hours use per day:12 hours24 hours + 12 hours
Number of days:7 days7 days
Total kWH:252 kWH252 kWH + 1260 kWH
Cost per kWH:$0.13$0.13
Total Cost per Week:$32.76$196.56

In cold weather, using emergency heat costs $163.80 more per week.

How Emergency Heat Works

Heat pumps work by transferring heat from the warmer outside air to the outside condensing coil. Heat pumps cool the refrigerant oil to a temperature much colder than the outside air.

The warm outside air goes over the coil and heats the refrigerant oil. The oil then goes to the evaporator coil. The cool interior air passes over the coil and gets heated. It is then distributed through the ductwork.

Emergency heat is a backup electrical coil that helps warm the air in your heat pump to provide heat. It uses electricity to heat electric coils to warm the air going into the ductwork.

At What Temperature Does Emergency Heat Turn On?

When it’s colder than 30 degrees Fahrenheit outside, the emergency heat will turn on. The emergency heat turns on because the heat pump can’t warm the home enough.

For example, picture a cold day outside, but inside the house, it’s warm. The heat pump can’t keep up with demand, so it uses emergency heat or the air conditioner to reach the desired temperature and keep it there.

Modern heat pumps can detect when it is necessary to have the emergency heat turned on. The best part is the energy it saves and the user’s peace of mind. This means your heat pump runs and uses emergency heat only when needed.

In our article, Will a Heat Pump Work in Subzero Temperatures? We detail how heat pumps operate in subfreezing temperatures.

When Should You Use Emergency Heat?

You should not need the emergency heat setting on your thermostat, even when it’s frigid cold. When it’s cold, the emergency heat will warm your home.

The only time to use this setting is if your heat pump stops working. This setting makes your backup heat run all the time, which is inefficient and expensive. If you increase the thermostat by more than 2 degrees, the emergency heat turns on.

We discuss emergency heat and 16 reasons your heat pump may not blow hot air.

The “emergency heat” option is only temporary until a repairman can fix your heat pump. Due to the way that backup heat works are much less energy efficient than your heat pump, so using it is best.

The heat pump will switch to emergency heat or backup heat if necessary but not if it’s unnecessary. If you have any questions about how your heat pump works, contact an HVAC contractor.

Is Emergency Heat Expensive to Run?

Emergency heat is expensive to run. Heat pumps are more efficient and cost less than electric backup heating strips. Heat pumps produce 1kw of heat with 1kw of energy, while heating strips use much more energy. This is one reason you should not use your emergency heat unless necessary. 

In dual-fuel heat pumps, the emergency heat runs on propane or natural gas. The cost may or may not cost more. In most cases, it will still cost more, but sometimes it can run without using extra fuel. 

In most cases, it’s safer to use your home’s regular heat setting instead of emergency heat or the gas furnace. Regardless of the weather, saving energy (electricity or gas) will save you money on heating.

heat pump iced lg

Auxiliary Heat vs. Emergency Heat – Are They the Same?

Auxiliary and Emergency heat are the same heat source. If you have both on your thermostat, the only difference is the name and purpose of use. When it gets too cold, the auxiliary heat comes on to help the heat pump. You can manually choose emergency heat, which makes the backup heat provide all the heating. 

Emergency heat is often referred to as auxiliary heat, backup heat, or electric heat strips. It is safe to assume that these all mean the same thing. It would help if you allowed your heat pump to do what it needs to unless something goes wrong. When the heat pump controls the auxiliary heat, you will save more energy (and thus money) than if you set your thermostat to emergency heating.

If unsure, consider where you’ll see the words “auxiliary heat” and “emergency heat.” Usually, “emergency heat” is a setting on your thermostat.

You can select it when necessary. However, “auxiliary heat” is not as commonly seen as a setting option in modern thermostats. It is the automatic function that your heat pump will switch on, thus not needing manual involvement to turn on. 

Why My Emergency Heat is Not Working

The most common reason that your emergency heat is not working is due to a lack of electricity. This can be due to a tripped circuit breaker or a faulty heating element.

If this is not the case, you can check inside the unit to ensure that the sequencer is working. A sequencer is a small circuit that controls the energy flow of a heat pump. It turns switches on and off based on the electrical setting. It puts different heating elements in order, aka “sequencing” them, to work in their respective turn.

Regular use of the heating system benefits the prevention of tripping the breaker or blowing the fuse by distributing energy.

To check if your heat pump’s sequencer is working correctly, use an electrical test meter. Before testing, make sure to turn off the power. If you are unsure how to do this safely, it is recommended to contact a local HVAC technician.

If you’re sure your sequencer isn’t the problem, check the electricity source. That’s usually why the emergency heat doesn’t work. 

To do this, the first thing you should do if you notice that your emergency heat is not working is to check the circuit breakers. If you flip them and they are working, then you can check the fuses. If you have an electric current checker, it is good to get enough volts to the unit.

You can verify this by looking up your specific unit and checking what its voltage should be. 

If all of this is good, it is time to inspect the machine. The sequencer inside of the box should be able to turn the emergency mode or auxiliary heat on. If this unit is bad, you will want to replace it.

Replacing any part of your heating system will bring lasting benefits to your home. It will improve your comfort and keep your home at the right temperature.

Emergency heat strips can also burn out, requiring replacement. Heat pumps will have two heat strips. If one fails, there is still one heat strip to provide heat to the home.

One heat strip or first-stage heating will not keep up with the demand for an extended time. It’ll also cause the system to run longer, consuming more energy.

Heat Pumps and Emergency Heat FAQs

Is it OK to run the heat pump on emergency heat?

Running a heat pump on emergency heat is inefficient and costly. It uses electric resistance heating, consuming more energy. Reserve it for extreme cold temperatures or system malfunctions. Avoid regular use to save on energy costs. Consult an HVAC professional for guidance.

At what temperature does a heat pump switch to emergency heat?

Heat pumps switch to emergency heat mode below 35-40°F, varying by system. It uses electric resistance heating when the heat pump can’t extract sufficient heat from the outdoor temperature unit. Using it often is costly; reserve it for extreme cold or system issues.

How much more expensive is emergency heat on a heat pump?

Emergency heat, or auxiliary heat, is much costlier than the primary heating pump mode because it uses electric resistance heating, consuming more electricity. This less efficient method can lead to higher energy bills. Using it sparingly during extreme cold is advisable for comfort, but continuous reliance can be expensive.

Do heat pumps work well in extreme heat?

Heat pumps work well to cool extreme heat by extracting indoor unit heat. However, in extreme heat, their heating efficiency drops as they struggle to extract enough warmth from the outdoor air. Supplemental heating may be needed.

Final Thoughts

To save energy and money, it’s important to know how heat pumps and emergency heat work. Heat pumps work well for heating homes above 30 degrees Fahrenheit. But, they have difficulty in cold weather. Emergency heat can fill the gap in certain situations. But, it costs more because it uses electric resistance heating.

When using emergency heat, remember it should not be the main heat source. It can make energy bills much higher. When needed, heat pumps can switch to emergency heat for efficient operation. The emergency heat setting on your thermostat is for temporary use. You should only use it until you fix your heat pump.

Emergency heat works well for warmth, but it costs more to use than the heat pump or electric furnace. To save money on heating, use the regular heat pump instead of relying on it constantly.


Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.