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

October 05, 2022

When the weather starts to cool off, you may be wondering about how you’ll make the most of your heating and cooling. After all, HVAC expenses routinely contribute a large portion of your monthly electric bill. To try and find ways to lower their HVAC bill, some owners look closely at their thermostat. Could there be a setting they can use to boost efficiency?

Most thermostats have a ‘Fan’ or ‘Fan On’ setting. But if the fan is running during a typical cycle, what can the fan setting offer for your HVAC system? This guide should help. We’ll share what exactly 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 the majority of thermostats, the fan setting indicates that the system's blower fan stays on. Some furnaces will generate heat at a low level with this setting, but in most cases heating or cooling isn’t being produced. The ‘Auto’ setting, conversely, will start the fan through a heating or cooling cycle and shut it off when the cycle is finished.

There are pros and cons to switching on the fan setting on your thermostat, and whether you do or don’t can depend on your distinct comfort needs.

Advantages to utilizing the Fan/On setting:

  • You can keep the temperature in each room more balanced by permitting the fan to keep circulating air.
  • Indoor air quality will be highest since steady airflow will keep passing airborne contaminants through the air filter.
  • A smaller number of start-stop cycles for the system's fan helps expand its life span. Since the air handler is often part of the furnace, this means you could minimize the risk of needing furnace repair.

Disadvantages to using the Fan/On setting:

  • A continuous fan could increase your energy expenses by a small margin.
  • Constant airflow could clog your air filter soon, 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 will sometimes stick around in unfinished spaces including the attic or an attached garage. If you keep the fan running, your HVAC system might draw 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 lead to needing AC repair more quickly as wear and tear increases.

The reverse can take place in the winter. Cooler spaces like a basement will hold onto cooler air, which will eventually flow into the rest of your home. Leaving the fan running could 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 use the fan/on setting, remember that every home and family’s comfort needs are different. 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 stressful on the family. Leaving the fan on can help to increase indoor air quality, helping your family breathe easier.

Your home has hot and cold spots. Lots of homes deal with persistent hot and cold spots that quickly return to a temperature different from the rest of the house. The fan setting can help limit these changes by steadily refreshing each room’s supply of air.