Season-by-Season Guide: Should My Thermostat Run on Auto or Fan?

October 05, 2022

When the weather is cooling off, you are probably thinking about how you’ll take full advantage of your heating and cooling. After all, HVAC bills routinely make up a large chunk of your monthly electric bill. To try and find ways to save, some owners take a closer look at their thermostat. Is there a setting they could use to improve efficiency?

The bulk of thermostats have a ‘Fan’ or ‘Fan On’ setting. But if the fan is on during a typical cycle, what will the fan setting provide for your HVAC system? This guide should help. We’ll share precisely what the fan setting is and when you can use it to save money over the summer or winter.

What Is the Fan Setting on My Thermostat?

For the majority of thermostats, the fan setting means that the air handler’s blower fan stays on. Some furnaces may continue to run at a low level in this setting, but in general heating or cooling isn’t being generated. The ‘Auto’ setting, in contrast, will turn on the fan over a heating or cooling cycle and turn it off when the cycle is complete.

There are benefits and drawbacks to trying the fan setting on your thermostat, and the ideal option should depend on your unique comfort requirements.

Advantages to trying the Fan/On setting:

  • You can keep the temperature throughout your home more uniform by allowing the fan to keep circulating air.
  • Indoor air quality should improve because constant airflow will keep forcing airborne pollutants through the air filter.
  • A smaller amount of start-stop cycles for the blower fan helps extend its life span. Since the air handler is usually part of the furnace, this means you could prevent the need for furnace repair.

Drawbacks to using the Fan/On setting:

  • A constant fan can add to your energy bills slightly.
  • Constant airflow may clog your air filter in a shorter amount of time, increasing the frequency you should replace it.

Should My Thermostat Be on Fan or Auto in Summer/Winter

Through the summer, warm air can persist in unfinished spaces such as the attic or an attached garage. If you leave the fan on, your HVAC system can gradually move this warm air into the rest of your home, pushing the HVAC system to work more to preserve the preferred temperature. In extreme heat, this can lead to needing AC repair more often as wear and tear increases.

The reverse can happen during the winter. Cooler spaces such as a basement will hold onto cooler air, which may eventually drift into the rest of your home. Keeping the fan on may pull more cold air upward, increasing the amount of heating you need to keep warm.

If you’re still trying to figure out if you should try the fan/on setting, remember that every home and family’s comfort needs will vary. Leaving the HVAC system’s fan on might work for you if:

Someone in your household deals with allergies. Allergies and other respiratory conditions can be hard on the family. Leaving the fan on should help to improve indoor air quality, helping your family breathe easier.

Your home has hot and cold spots. Lots of homes wrestle with difficult hot and cold spots that quickly return to a temperature different from the rest of the house. The fan setting should help limit these changes by consistently refreshing each room’s ventilation.