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

October 05, 2022

When the weather is cooling off, you might be thinking about how you’ll prepare your heating and cooling. After all, HVAC bills can make up a big piece of your monthly electric bill. To learn new ways to save, some owners take a closer look at their thermostat. Could there be a setting they should use to improve efficiency?

The majority of thermostats come with a ‘Fan’ or ‘Fan On’ setting. But if the fan is on during a typical cycle, what does the fan setting provide for an HVAC system? This guide can help. We’ll review just what the fan setting is and how you can use it to save money in the summer or winter.

What Is the Fan Setting on My Thermostat?

For the bulk of thermostats, the fan setting means that the HVAC blower fan keeps running. Certain furnaces can run at a low level with this setting, but in general heating or cooling isn’t being made. The ‘Auto’ setting, on the other hand, will turn on the fan over a heating or cooling cycle and turn it off once the cycle is finished.

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

Advantages to switching to the Fan/On setting:

  • You can keep the temperature in every room more uniform by permitting the fan to keep running.
  • Indoor air quality will be highest since constant airflow will keep forcing airborne contaminants into the air filter.
  • A smaller number of start-stop cycles for the system's fan helps extend its life span. Because the air handler is typically a component of the furnace, this means you might prevent the need for furnace repair.

Downsides to using the Fan/On setting:

  • A constant fan can add to your energy expenses by a small margin.
  • Continuous airflow may clog your air filter soon, increasing the frequency you should replace it.

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

Through the summer, warm air can stick around in unfinished spaces including the attic or an attached garage. If you keep the fan running, your HVAC system may pull this warm air into the rest of your home, forcing the HVAC system to run longer to keep up with the preferred temperature. In extreme heat, this could result in needing AC repair more quickly as wear and tear grows.

The opposite can occur over the winter. Cooler spaces such as a basement will hold onto cooler air, which will eventually make its way into the rest of your home. Leaving the fan setting on may pull more cold air upward, increasing the amount of heating you need to stay warm.

If you’re still trying to figure out if you should try the fan/on setting, don’t forget that every home and family’s comfort needs will vary. Leaving the HVAC system’s fan on could work for you if:

Someone in your household deals with allergies. Allergies and other respiratory conditions can be tough on the family. Leaving the fan on is more likely to increase 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 can help lessen these changes by constantly refreshing each room’s supply of air.