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

October 05, 2022

Once the weather begins to cool off, you are probably concerned about how you’ll make the most of your heating and cooling. After all, HVAC expenses routinely contribute a large piece of your monthly electric bill. To figure out new ways to lower their HVAC bill, some owners take a closer look at their thermostat. Maybe there’s a setting they could use to improve efficiency?

Most thermostats include both a ‘Fan’ or ‘Fan On’ setting. But if the fan is running during a typical cycle, what will the fan setting provide for the HVAC system? This guide can help. We’ll walk through just what the fan setting is and when you can use it to cut costs during the summer or winter.

What Is the Fan Setting on My Thermostat?

For most thermostats, the fan setting means that the air handler’s blower fan remains on. Certain furnaces can operate at a low level in this setting, but in most cases heating or cooling isn’t being generated. The ‘Auto’ setting, conversely, will start the fan during a heating or cooling cycle and shut it off when the cycle is finished.

There are advantages and disadvantages to switching on the fan setting on your thermostat, and the ideal option will depend on your distinct comfort preferences.

Advantages to utilizing the Fan/On setting:

  • You can keep the temperature throughout your home more consistent by enabling the fan to keep circulating air.
  • Indoor air quality should improve since continuous airflow will keep moving airborne contaminants through the air filter.
  • A smaller number of start-stop cycles for the HVAC fan helps extend its life span. As the air handler is often a component of the furnace, this means you could avoid needing furnace repair.

Downsides to switching to the Fan/On setting:

  • A nonstop fan can raise your energy costs somewhat.
  • Continuous airflow can clog your air filter soon, increasing the frequency you will want to replace it.

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

During the summer, warm air will sometimes persist in unfinished spaces such as the attic or an attached garage. If you keep the fan running, your HVAC system might pull this warm air into the rest of your home, compelling the HVAC system to work more to preserve the desired temperature. In extreme heat, this can lead to needing AC repair more quickly as wear and tear gets worse.

The reverse can occur in the winter. Cooler spaces such as a basement will hold onto cooler air, which can eventually drift into the rest of your home. Keeping the fan on could 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 switch to the fan/on setting, remember that every home and family’s comfort needs are different. Leaving the HVAC system’s fan on might be best for you if:

Someone in your household deals with allergies. Allergies and similar respiratory conditions can be tough on the family. Leaving the fan on is more likely to enhance indoor air quality, helping your family breathe easier.

Your home has hot and cold spots. Many homes wrestle with stubborn hot and cold spots that quickly return to a temperature different from the rest of the house. The fan setting should help lessen these changes by steadily refreshing each room’s supply of air.