If you already have a heat pump, you may be wondering about some of the different settings mentioned in the instructions or indicated on the remote control. While these terms can seem intimidating at first, with some basic understanding, you’ll be able to better adjust your new heat pump and understand when something has gone awry.

Perhaps the first terms you’ll see are “auxiliary heat” and “emergency heat.” In this post, we’ll look to answer the question “What does auxiliary heat mean?” and dive into any differences between auxiliary heat vs. emergency heat.


Auxiliary heat, emergency heat, radiant heat, and strip heat are terms that generally refer to the same thing: your heat pump’s electric heat strips. These heat strips offer a form of heat similar to an electric space heater that uses coils that become super-heated to warm the air around it. This differs from the typical way your heat pump warms your home, which uses refrigerant to transfer heat where it’s needed.

If there is a difference between heat pump auxiliary heat and emergency heat, it’s subtle. Auxiliary heat gets its name from the “AUX” symbol that appears on your heat pump’s controls when, under the normal heating operation, your system automatically switches on the heat strips. Two common scenarios for the heat strips turning on is when the outside unit needs defrosting or when the low outdoor temperatures cause performance issues for the normal operation of the heat pump.

Emergency heat, on the other hand, is a manual setting selected by the user to turn on strip heat. If your outdoor unit is damaged or malfunctioning, you can select this setting to turn on the heat strips without waiting for them to triggered by automation.

To summarize, while these terms can be used interchangeably and refer to the same type of heat, auxiliary heat is when your heat pump’s heat strips turn on automatically. Emergency heat is when the heat strips turn on due to you manually selecting the emergency heat setting.


Not all heat pumps offer auxiliary heat. In places with moderate winters that never hit the freezing point, auxiliary heat is unnecessary, as it would most likely never click on.

Some residential spaces may also prefer to pair a different type of heating system with their heat pump. Dual systems that include geothermal heat, natural gas, or other generators of heat can work in conjunction with heat pump systems, so if temperatures drop too low, there is still a form of operational heat.


Your heat pump’s auxiliary heat should turn on whenever the outdoor unit can no longer efficiently transfer heat inside. This can happen in multiple scenarios, but most often, when outdoor temperatures drop below 35 to 40 degrees Fahrenheit. Another potential use is when the outdoor unit requires defrosting to function.

Auxiliary heating should also turn on when your room’s temperature is three degrees colder than the thermostat setting. This is a sign that heat is no longer being transferred easily from the outdoor unit to the interior heat pump. If the indoor temperature struggles to catch up to the desired setting even as outdoor temperatures rise, this can be an indication your heat pump is low on refrigerant due to a leak or another cause.


While the auxiliary heat turns on somewhat regularly in cold temperatures, if you notice it never turns off or is in constant use, you may find yourself with a higher energy bill at the end of the month. Auxiliary heat is more expensive and less efficient than the heat pump’s typical operation, so while it may keep your warm, it can affect your budget.

There are a couple of ways to reduce the need for auxiliary heat. When outdoor temperatures drop to around freezing, you shouldn’t keep your thermostat set to higher temperatures to compensate. If it’s 25 degrees Fahrenheit outside, you should keep your thermostat in the high-60’s or low-70’s at maximum.

If you have a dual-fuel heating system, you should also switch from your heat pump to your other heating sources as temperatures dip to near freezing. A gas furnace, for instance, may still not be as efficient as your heat pump, but it far exceeds the auxiliary heat’s efficiency.

By keeping an eye on your thermostat and planning for lower temperatures, you should be able to help mitigate the constant use of more expensive and less efficient auxiliary heat while keeping your home heated. Of course, in a pinch, a comfy sweater can help, too.


The first time your heat pump’s auxiliary heat switches on, you may notice a slight burning smell. This can be alarming, but if there’s no indication of smoke or flame, you will not need to contact the fire department.

One of the most common sources of this burning smell is dust that has collected on the heat strips. If you haven’t turned on your heat in a while, this dust may start to burn and give off an acrid smell. This smell should dissipate within a day. So, there’s no cause for concern unless you notice the odor linger into the next day.

Another typical source is a clogged or dirty air filter. A clogged filter makes the heat pump work extra hard to push heat into your room, which can cause a burning smell. You should clean your air filters at least once a season but preferably once a month.

If you still smell burning after a day of use and cleaning your air filter, this may be a sign of an electrical issue. In this case, it’s best to turn off the heat pump and contact us immediately.


As the Pacific Northwest’s heat pump experts, The Heat Pump Store stands ready to answer any questions you may have. Contact us today by calling 877-509-2691 or visit our showrooms in Eugene, Portland, and Salem.