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

Author: Mr. Tre Morar V  |  Last update: Tuesday, March 10, 2026

Auixiliary Heat will turn on automatically when heat can no longer efficiently transfer heat from the outside air to heat pump. This is when the outside is around 35-40 degrees and the indoor temperature is around three degrees cooler than the thermostat setting.

Does a heat pump automatically switch to auxiliary heat?

If the temperature outside is below freezing, your heat pump's auxiliary heat system will come on automatically - whether that's a gas furnace or electric heat strips. But there are some things you can do to minimize the need for aux heat. Make sure your heat pump is correctly sized for your home.

At what temperature should auxiliary heat come on?

Homeowners should expect auxiliary heat to turn on during colder temperatures, especially under 40 degrees. Your heat pump is an amazing appliance that can efficiently extract warmth from the outdoor air and transform it into cozy comfort inside your home.

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

This is where emergency heat comes in. Typically, this setting on your thermostat kicks on when the temperature is anywhere between 30 to 35 degrees Fahrenheit. How your emergency uses this air differs from the normal way that your heat pump usually functions.

Why is my heat pump not switching to auxiliary heat?

Aux Heat Will Not Turn On

One of the most common causes of a heat pump system or auxiliary heat not turning on is a blown fuse or tripped circuit breaker. Start by checking your fuse box or circuit breakers.

Heat Pump Notification of AUXILIARY HEAT

What happens if auxiliary heat runs too long?

This can cause concern, as auxiliary heat typically is not supposed to run all the time. While it's normal for auxiliary heat to kick in during exceedingly cold temperatures, running it too long may indicate an issue with the heat pump.

Can you run heat pump without auxiliary heat?

Some heat pumps are designed operate independently without back up heating, while others are designed to use a back up heating system. Whether or not you need a backup heat source for your heat pump will depend on the type of heat pump you purchase, your climate zone, and the design and efficiency of your home.

What temperature is too cold for heat pumps?

Most standard heat pumps will function at 100% efficiency until the outside temperature reaches about 40° F. However, when the temperature dips below this, most heat pumps are not able to maintain efficiency. They become much less effective at temperatures between 20° F to 30° F.

What is the difference between auxiliary heat and emergency heat?

Auxiliary Heat – This is the secondary heat source that turns on automatically. Emergency Heat – This is when you turn on the secondary heat source.

At what temperature should you switch from heat pump to furnace?

With a typical operation of a hybrid heating system, the heat pump will operate with ambient temperatures above 32 degrees. When temperatures are below 32 degrees, the gas furnace will operate.

What triggers auxiliary heat?

Auxiliary heat is a secondary heating function your thermostat automatically switches to when it's too cold outside for your heat pump to extract warmth from the air. This type of heating is often triggered when the outdoor temperature drops to near or below-freezing temperatures.

What is stage 2 heat on a heat pump?

What is meant by Stage Two heating? When the thermostat on a dual-stage furnace reads “Stage 2,” it implies that the furnace is operating at the higher setting, giving you 100 percent of its capacity. Usually, the lower setting of a dual-stage furnace is sufficient to provide household comfort almost 80% of the time.

What is the normal temperature for auxiliary?

Normal temperature is around 98.6°F (37°C). But it can range from 97.6°F to 99.6°F (36.4°C to 37.6°C). Armpit temperatures can range from 0.5°F to 1°F (0.3°C to 0.6°C) lower than a rectal temperature. Before putting the thermometer away, clean it with soap and warm water or alcohol.

What temperature to turn on auxiliary heat?

Auixiliary Heat will turn on automatically when heat can no longer efficiently transfer heat from the outside air to heat pump. This is when the outside is around 35-40 degrees and the indoor temperature is around three degrees cooler than the thermostat setting.

Can a heat pump switch from heating to cooling automatically?

The Auto mode on heat pumps allows the heat pump to decide whether to heat or cool the space, but it doesn't always know best. “Auto” mode could cause your heat pump to heat on a cool summer night or cool on a sunny fall or winter afternoon. To avoid accidentally cooling during the fall and winter, use “Heat” mode.

Why does my HVAC keep switching to auxiliary heat?

With some newer thermostats, the auxiliary heat may turn on if the temperature does not rise quickly. Your HVAC technician might reprogram your thermostat or recommend a different model. Older thermostats, on the other hand, are more likely to malfunction, which can also trigger auxiliary heat.

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

This heating method works incredibly efficiently until the outdoor temperature reaches about 35 degrees. At this point, the heat pump has difficulty extracting enough heat from outside to keep up with the thermostat setting. This is when many people assume it's time for switching their heat pump to emergency heat.

Does auxiliary heat run up your electric bill?

Auxiliary heat strips supplement the heat pump and produce warm air to quickly heat your home. Those heat strips use substantially more energy and will increase your electric bill.

Why is my auxiliary heat blowing cold air?

The heat pump itself might have a problem that needs to be addressed as soon as possible. There could be a refrigerant leak, or the reverse valve is malfunctioning. Either issue prevents the unit from blowing warm air in heating mode, requiring immediate attention from an HVAC technician.

What is the 20 degree rule for heat pumps?

Simply put, it means you should never set your thermostat for a temperature more than 20 degrees cooler than the outside air. Why not? Most air conditioning systems can only handle a 20-degree difference between the outside and inside air temperatures.

At what outside temperature does a heat pump become ineffective?

Heat pumps do not operate as efficiently when temperatures drop to between 25 and 40 degrees Fahrenheit for most systems. A heat pump works best when the temperature is above 40. Once outdoor temperatures drop to 40 degrees, heat pumps start losing efficiency, and they consume more energy to do their jobs.

Should I turn off my heat pump in extreme cold?

People do not need to turn their heat pumps off. Residents should make sure their supplemental home heating systems are on and operating. Set the thermostats to a degree or two lower than heat pumps.

How does a heat pump know when to switch to auxiliary heat?

Aux heat will kick on when your heat pump cannot deliver enough warmth to heat your home. Typically, your heat pump will energize the auxiliary heat strip inside your secondary heating source to help reach its set temperature faster.

Does heat pump shut off when auxiliary heat is on?

If the heat pump can't keep up with the demand for heating, then your auxiliary heat would come on. Then both would be running. On the other hand, if it is so cold outside that the heat pump can't make heat efficiently, it should shut down in favor of the less costly 100% gas heat.

Should my thermostat say auxiliary heat?

Your aux heat indicator signifies that your heat pump needs some extra help reaching your desired temperature setting. When you see aux heat on the thermostat, you'll know your heat pump is attempting to energize the auxiliary heat strip inside your secondary heating source.

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