How Do I Know If I Have a Heat Pump with Auxiliary Heat?

Sometimes you don’t even need to know. If the auxiliary heat function is present on your heat pump, it will kick on automatically without further effort on your part. This way, you don’t have to bother with supplemental heat sources during extremely cold weather.

Unfortunately, auxiliary heat can sometimes present a few challenges. For instance, the auxiliary heat function may refuse to kick in even after countless attempts. Meanwhile, others may kick into action but fail to function as intended.

In this case, knowing a few things about the heat pump’s auxiliary heating system, how it works, and how to troubleshoot common issues may help. Let’s begin with a definition.

What’s Auxiliary Heat?

Auxiliary heat, or aux heat, refers to an additional (or supplementary) heating component on a heat pump. Its main purpose is to provide extra heat alongside the heat pump whenever the heat pump cannot draw enough heat to keep your home warm and comfortable.

This often happens when it gets too cold outside. Temperatures can drop significantly during the winter months. Sometimes a few areas experience temperatures as low as 30˚F. Heat pumps aren’t very reliable under such cold conditions because there isn’t much heat to extract from the outdoor air.

Moreover, heat pumps need to keep their internal components warm during extremely cold weather. It’s why your heat pump defrosts a lot more in the heart of winter.

Defrost cycles focus on ridding the outdoor condenser of frost that forms inside and outside the condenser when it gets too cold outside. Otherwise, the freezing can damage condenser coils and the entire heat pump.

With the heat pump incapacitated and the little heat it produces constantly needed elsewhere, a heat pump may leave battling biting cold at the time when you need home heating most. That’s where auxiliary heaters come in handy.

How the Auxiliary Heater Works

Auxiliary heaters are primarily radiant heat strips built in to the heat pump to “burn” electricity to produce heat. Unlike the heat pump, which extracts heat from outdoor air and dumps it inside the house to raise indoor temperatures, auxiliary heaters use high resistance strips to convert electric current into heat.

However, some heat pumps may have auxiliary heating without an in-built auxiliary heating system. Instead, these systems rely on external heat sources.

For instance, the heat pump can be directly wired to a natural gas heater or hot water heating system. When temperatures fall below the specified mark, the heat pump signals the external sources to generate supplemental heat.

In both arrangements, though, auxiliary heating is controlled from the heat pump thermostat. More importantly, aux heat engagement is automatic. The auxiliary heat source will kick into action automatically without further intervention on your part.

How Do You Know that You Have Auxiliary Heating?

Although most heat pumps, especially modern models, have auxiliary heating, not all models do. There are four broad ways to know if your unit has aux heat;

1. Check the user manual

If your heat pump has an auxiliary heater, the manufacturer will likely mention it in the user manual. Most manufacturers mention it towards the end of the manual, though you can also check the contents page. Check for words such as “supplemental heat,” “auxiliary heat,” and “aux heat.”

A key advantage of checking with the user manual is that it will likely have more information on using the feature. For instance, it will tell you whether you can turn on aux heat manually and what to do if the aux heat feature malfunctions.

2. Look at the air handler closely

Heat pumps with auxiliary heat contain a unique feature on the air handler conspicuously missing from those without aux heat – electrical resistance coils.

If the heat pump has a built-in auxiliary heating system, it will have electric resistance coils in the air handler. Some also use finned electric elements. Either way, models without aux heat don’t have these additional coils.

The only problem is that you need to open the air handler to see the coils. If you’re not scared, the fans are easily visible when you remove the air handler lid.

3. Look at the thermostat

We’d have had this at number, except that some thermostats are built-in, meaning that you may not easily tell whether the aux function is present. However, if your heat pump uses a wall thermostat, you should tell with ease if it has auxiliary heat.

The aux heat function typically appears as a setting on wall thermostats. The name might vary depending on the heat pump brand. But, again, check for terms such as “aux heat” and “auxiliary heat.” Some also indicate “heat,” which can be a little confusing.

4.Observe the heat pump at work

If you live in a region with extreme winters, you can also know you have auxiliary heating if heating performance isn’t affected when temperatures dip below 31˚F. Very rarely do heat pumps perform well at such low temperatures. Some mini-split systems are designed to go off altogether when temperatures drop below 35˚F.

If outdoor temperatures are lower than that (around 35˚F, though others start at 40˚F), it’s almost certain that you have auxiliary heating. 

Aux Heat as a “Potential Add-On”

As we’ve mentioned, some heat pumps are designed to allow you to wire the system to external heat sources for auxiliary heating.

We must also mention that a few units can have the optional aux heat feature but require that the auxiliary heating system is installed within the heat pump. These units usually indicate aux heat as an “add-on.”

In both cases, the choice is yours. You can install the auxiliary heater or choose to neglect it. We’d strongly recommend that you install it. It’s a great way to protect yourself from extremely cold conditions when the heat pump is overwhelmed.

Aux Heat vs. Emergency Heat

As we conclude, it’s also vital to understand the difference between auxiliary heat and emergency heat. Sometimes people confuse the two. Although both are important, they aren’t the same thing.

More importantly, although the more advanced heat pumps have both, some have only one while others lack both.

  • Aux heat is supplementary

Auxiliary heat steps up to complement the heat pump. It doesn’t take over all heating responsibilities. Instead, it merely tops up the balance to ensure that your home is warm and comfortable throughout. The two often run simultaneously.

  • Emergency heat is a replacement

It replaces the heat pump in case the heat pump stops working. It will never run alongside the heat pump. Instead, it only steps in when the heat pump is out. As soon as the heat pump returns to function, the emergency heater shuts down.

Key Takeaway

Auxiliary heat is critical, especially if you live in a colder part of the country where temperatures occasionally drop below 40˚F. At this temperature, the heat pump may not be able to provide enough heat to keep you warm and cozy. The auxiliary heater will step in to fill the balance.

Unfortunately, not all heat pumps have auxiliary heaters. If you want to find out if your heat pump has one, check the user manual, the thermostat, or the air handler. You can also tell that the heat pump has auxiliary heating if heating levels don’t fall even at temperatures below 35˚F.