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

October 05, 2022

When the weather starts to cool off, you might be concerned about how you’ll take full advantage of your heating and cooling. After all, HVAC costs can add up to a significant piece of your monthly electric bill. To learn new ways to lower their HVAC bill, some homeowners look closely at their thermostat. Could there be a setting they can use to improve efficiency?

The bulk of thermostats come with a ‘Fan’ or ‘Fan On’ setting. But if the fan is on during a normal cycle, what will the fan setting provide for the HVAC system? This guide can help. We’ll review precisely 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 indicates that the air handler’s blower fan keeps running. A few furnaces will run 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 through a heating or cooling cycle and shut it off after the cycle is over.

There are benefits and drawbacks to switching on the fan setting on your thermostat, and the ideal option will depend on your personal comfort needs.

Advantages to switching to the Fan/On setting:

  • You can keep the temperature in every room more consistent by allowing the fan to keep running.
  • Indoor air quality should improve as continuous airflow will keep passing airborne contaminants through the air filter.
  • A smaller amount of start-stop cycles for the HVAC fan helps extend its life span. Since the air handler is usually a component of the furnace, this means you can minimize the risk of needing furnace repair.

Disadvantages to using the Fan/On setting:

  • A nonstop fan will likely add to your energy bills somewhat.
  • Constant airflow could 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 may linger in unfinished spaces like the attic or an attached garage. If you use the fan setting, your HVAC system may pull this warm air into the rest of your home, compelling the HVAC system to work more to preserve the set temperature. In severe heat, this could result in needing AC repair more often as wear and tear increases.

The opposite can happen over the winter. Cooler spaces such as a basement will hold onto cooler air, which may eventually drift into the rest of your home. Leaving the fan running could pump more cold air upward, increasing the amount of heating you need to stay 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 be ideal 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 deals with hot and cold spots. All kinds of homes deal with stubborn hot and cold spots that quickly shift to a temperature different from the rest of the house. The fan setting should help limit these changes by steadily refreshing each room’s ventilation.