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What Is Auxiliary Heat?

Do you own a heat pump? If so, you might have noticed the letters AUX heat” on your thermostat and wondered what it means. 

Put simply, it refers to a backup heating source for your heat pump. AUX” refers to auxiliary” heat and the setting turns on when your heat pump’s efficiency drops due to extremely cold outdoor temperatures. 

To help explain more about this setting and why it comes on, in this blog, we’ll review:

You can also check out our blog, Heat Pump vs. Furnace in Colorado: Which Is Better?” for further reading about reliable heating systems for Colorado homeowners.

Need heating advice from Colorado experts?

Contact Cooper Heating and Cooling! Since 1978, our highly trained technicians have supported Colorado homeowners with 5‑star heating services. Whether you need a heat pump replacement, repair, or maintenance, we’ve got you covered with convenient scheduling and honest pricing. Call us at (720) 605‑7270 or book online below.

How Your Heat Pump Works

Before we look at auxiliary heat, it’s important to understand how heat pumps work. As you may know, a heat pump is a two-in-one heating and cooling system. While there are some different types, air-source heat pumps are the most common.

Air source heat pumps operate by transferring heat rather than creating it. During colder months, the heat pump absorbs heat from the outdoor air, even in low temperatures, using a refrigerant fluid that evaporates at low temperatures. This fluid is then compressed, increasing its temperature, and the resulting high-temperature gas releases heat into the indoor space. In the warmer months, the process can be reversed for cooling, where the heat pump absorbs heat from the indoor air and releases it outside. 

This dual functionality makes air source heat pumps a sustainable alternative to traditional heating and cooling systems, as they can transfer rather than generate heat, using less energy and reducing greenhouse gas emissions. However, they may struggle with heating when the temperature drops below freezing. This is why it’s also recommended to have an auxiliary or supplementary heat source.

Extremely Cold Weather Conditions

We’ve reviewed how heat pumps work and answered, What does auxiliary heat mean?” Now, it’s time to explore why AUX heat mode occurs in the first place. 

The main reason why your heat pump may switch to AUX heat is because it’s extremely cold outside. If temperatures fall below 32 ºF, the system may have difficulty extracting enough warm air from outside. To adequately heat your home, it will turn to the backup source.

Backup Heating System

Now that you know why AUX heat is important, you might wonder: What type of backup heating systems can you have? Most homeowners choose between the following options:

  • Electric resistance coil heaters
  • Gas furnaces

Electric resistance coil heaters are installed directly in your home’s ductwork. Gas furnaces, meanwhile, are separate appliances that run on natural gas. TheEnergy Efficiencyy’re usually more efficient and reliable than electric resistance coil heaters but are also more expensive.

Energy Efficiency

A common question homeowners ask when they notice the AUX heat” message is, Is it bad if auxiliary heat comes on?” The answer depends on the circumstances. If it’s very cold outside, or if your heat pump has frozen over, then AUX heat is normal. However, if AUX heat is on and it’s over 40 ºF outside, then there may be a problem with your heat pump. 

This brings us to a second question: What happens if AUX heat turns on unnecessarily? The most significant consequence is decreased energy efficiency. AUX heat mode consumes more energy because it involves two heat sources (your heat pump and backup source). This leads to higher energy bill costs, which may be up to 50% higher during AUX heat mode.

What to Do If AUX Heat Keeps Turning On

While it’s normal for your heat pump to switch to AUX heat mode every now and then, this shouldn’t be a frequent occurrence. And it definitely shouldn’t happen in the summer.

When AUX heat keeps turning on, the first thing you should do is check your thermostat settings. If you accidentally set it to a very high temperature, your heat pump may use the backup source to fulfill these needs. If your settings are normal, the best thing to do is contact HVAC professionals, such as the Cooper Heating and Cooling team.

Need a Heat Pump Repair? The Cooper Green Team Is On the Way!

Our team has over 40 years of experience providing top-notch heating services throughout Denver and Colorado’s front range. Whether you need a repair, maintenance, or upfront quote on a heat pump installation, you can trust us to get it done quickly and efficiently. Call us at (720) 605‑7270 or request service through our website below.

Luke Cooper

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