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

October 05, 2022

As the weather starts to cool off, you are probably wondering about how you’ll prepare your heating and cooling. After all, HVAC bills routinely add up to a large portion of your monthly electric bill. To learn new ways to reduce costs, some owners look closer at their thermostat. Could there be a setting they should use to increase efficiency?

The bulk of thermostats come with a ‘Fan’ or ‘Fan On’ setting. But if the fan is running during a normal cycle, what will the fan setting offer for your HVAC system? This guide should help. We’ll review just 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. A few furnaces may continue to run at a low level with this setting, but for the most part heating or cooling isn’t being produced. The ‘Auto’ setting, on the other hand, will run the fan over a heating or cooling cycle and shut it off after the cycle is over.

There are advantages and disadvantages to using the fan setting on your thermostat, and whether you do or don’t will depend on your unique comfort preferences.

Advantages to trying the Fan/On setting:

  • You can keep the temperature in each room more balanced by enabling the fan to keep circulating air.
  • Indoor air quality will be highest since continuous airflow will keep passing airborne pollutants through the air filter.
  • A smaller number of start-stop cycles for the system's fan helps expand its life span. Because the air handler is typically a component of the furnace, this means you could avoid needing furnace repair.

Drawbacks to utilizing the Fan/On setting:

  • A nonstop fan can increase your energy costs slightly.
  • Constant airflow may clog your air filter in a shorter amount of time, increasing the frequency you’ll need to replace it.

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

Through the summer, warm air can stick around in unfinished spaces such as the attic or an attached garage. If you use the fan setting, your HVAC system may gradually move this warm air into the rest of your home, pushing the HVAC system to work harder to keep up with the set temperature. In severe heat, this may lead to needing AC repair more quickly as wear and tear gets worse.

The opposite can happen during the winter. Cooler spaces like a basement will hold onto cooler air, which may eventually flow into the rest of your home. Leaving the fan running will sometimes pump more cold air upward, increasing the amount of heating you need to remain warm.

If you’re still trying to determine if you should switch to the fan/on setting, keep in mind that every home and family’s comfort needs are different. Leaving the HVAC system’s fan on may work for you if:

Someone in your household suffers from allergies. Allergies and similar respiratory conditions can be hard on the family. Leaving the fan on is more likely to improve indoor air quality, helping your family breathe easier.

Your home deals with hot and cold spots. Many homes wrestle with persistent hot and cold spots that quickly evolve to a temperature different from the rest of the house. The fan setting might help minimize these changes by constantly refreshing each room’s airflow.