If you take a closer look at your thermostat, you may notice an “Aux Heat” setting and many people don’t know what this does. This is the setting that a heat pump will defer to automatically when the outdoor temperatures are too cold for the equipment to warm the home to a desired temperature. This is not a heat setting that you would use constantly and you may be tempted to contact an HVAC specialist to deal with the “problem”. With a fuller understanding of how a heat pump and the Aux Heat setting works, you have more information to make decisions.

Heat Pumps 101

A heat pump can heat a home by pulling heat into the home from the outdoors, and it can cool the home by pushing heat out of the home. In a very real sense, a heat pump doesn’t generate heating or cooling by itself. They simply transfer coolness or warmth from one location to another using a circulatory system filled with refrigerant. The refrigerant flows from the heat pump condenser outdoors to the air handler indoors and back again to make temperature changes. In a milder climate, a heat pump is an energy efficient way to cool or heat a home. But, if there is a sudden temperature change, most people would turn to a secondary heating source to keep the home comfortable. When the freezing winter temperatures arrive, the Aux Heat setting is automatically triggered.

Aux Heat 101

This is the secondary heating setting that the thermostat switches to automatically when the external temperatures are too cold. The heat pump simply cannot extract sufficient warmth from the air outdoors to make the home feel warmer. Auxiliary heat is often a setting that you notice when the external temperature approaches or reaches below freezing. This is also the setting that turns on when a heat pump is in defrost mode to prevent the introduction of cold air into a home when the outdoor condenser unit is thawing.

Auxiliary heat will turn on when the system recognizes that some extra help is required to achieve the comfortable temperature that’s set on the thermostat. An auxiliary heat strip is turned on to energize the heating performance to add warmth to the home. The temperature that you set on the thermostat is the main trigger that starts the Aux Heat. If the thermostat sensor detects a drop of 1-2º below the set temperature limit, the Aux Heat will kick in.

The Aux Heat setting will also be activated automatically if the heat pump is covered in ice and/or snow. If ice forms on the Aux Heat strip this will prevent the equipment from defrosting which can damage the equipment. This scenario can also occur if the refrigerant levels are too low or the outdoor motor fans are damaged. The Aux Heat setting can be noticed on the thermostat with an indicator. This could be a small flashing light or an Aux Heat digital reading on the thermostat display.

4 Aux Heat Tips

If the Aux Heat setting turns on, there are four tips that you can follow to prevent this heating system from inefficient heating over the long term. They are:

  • The 30 Minute Check: The Aux Heat setting is designed to be a temporary solution, and if it turns on, check it after 30 minutes to see if it’s turned off again.
  • Make Minor Temperature Adjustments: Adjust the thermostat in 1-2º increments to prevent the Aux Heat from turning on if the temperature drops below the thermostat setting by a few degrees.
  • Avoid Using Emergency Heat: Don’t resort to the use of emergency heat settings unless there truly is a heating emergency. A heat pump needs time to draw heat into the home, and emergency heat consumes a lot of extra energy.
  • Check the Outdoor Temperature: When the external temperature reaches 40º or higher, the Aux Heat should turn off. If it stays on, there may be a problem, and you need to contact an HVAC technician.

How to Identify Heat Pump Problems

The best way to avoid and prevent heat pump problems is to invest in regular preventative maintenance. Identifying and fixing emergent issues at an earlier stage will be less expensive than a more extensive repair later. The technician can make adjustments that will improve the performance and energy efficiency. Let’s look at three potential problems and their possible causes.

1.   The Heat Pump Won’t Turn On

If the heat pump won’t turn on, there may be a simple fix, check that the thermostat is set to heat and that the equipment is receiving power. If this doesn’t fix the problem, the most likely problems are a reversing valve or heat pump start capacitor issue. Contact a local HVAC specialist to identify the cause and make the necessary repairs.

2.   The Heat Pump is Not Heating the Home

Check the outdoor unit, it may be blocked under snow, ice, or with some fallen branches or shrubbery. Inside, the air filter may need to be changed or cleaned to allow the air to pass through efficiently. If these are not the cause of the problems, it’s time to get the refrigerant levels checked by an EPA certified HVAC technician for safety, performance, and efficiency.

3.   The Heat Pump Runs Constantly

If a heat pump is running constantly, it will damage the equipment, drive up the energy bills and shorten the lifespan of the equipment. Check the thermostat to ensure that the system is not set to Aux Heat and clean or replace the air filter. If these simple fixes don’t work, the most likely problem is a broken compressor unit. Contact your local HVAC technician, and this can replace this crucial component for you to restore normal operations.

In Conclusion

The best way to support your heat pump is to schedule regular annual maintenance for the system. Some other passive ways to improve heating performance are checking doors and windows for cracks that can be sealed. Adding more insulation to the attic space is a great way to keep the warmer air indoors when the weather is colder.

If you want to schedule some essential maintenance for your heat pump, contact your local heating and cooling specialist.