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

October 05, 2022

As the weather begins to cool off, you may be concerned about how you’ll prepare your heating and cooling. After all, HVAC costs can contribute a significant portion of your monthly electric bill. To learn new ways to reduce costs, some people look closely at their thermostat. Could there be a setting they should use to improve efficiency?

The majority of thermostats have a ‘Fan’ or ‘Fan On’ setting. But if the fan is going during a normal cycle, what will the fan setting offer for an HVAC system? This guide can help. We’ll share just what the fan setting is and how you can use it to reduce costs during 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 remains on. Certain furnaces will generate heat at a low level with this setting, but in most cases heating or cooling isn’t being made. The ‘Auto’ setting, conversely, will run the fan during a heating or cooling cycle and shut it off when the cycle is finished.

There are pros and cons to using the fan setting on your thermostat, and the ideal option will depend on your unique comfort needs.

Advantages to utilizing the Fan/On setting:

  • You can keep the temperature throughout your home more consistent by allowing the fan to keep running.
  • Indoor air quality should improve as constant airflow will keep moving airborne contaminants through the air filter.
  • A smaller amount of start-stop cycles for the system's fan helps lengthen its life span. Because the air handler is usually part of the furnace, this means you could prevent the need for furnace repair.

Disadvantages to utilizing the Fan/On setting:

  • A constant fan will likely raise your energy costs somewhat.
  • Continuous airflow could clog your air filter up more quickly, increasing the frequency you should replace it.

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

During the summer, warm air may persist in unfinished spaces such as the attic or an attached garage. If you use the fan setting, your HVAC system might pull this warm air into the rest of your home, compelling the HVAC system to work harder to preserve the set temperature. In severe heat, this can lead to needing AC repair more quickly as wear and tear grows.

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 may pull more cold air upward, increasing the amount of heating you need to remain warm.

If you’re still trying to decide if you should switch to the fan/on setting, remember that every home and family’s comfort needs will vary. 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 stressful on the family. Leaving the fan on should help to enhance indoor air quality, helping your family breathe easier.

Your home experiences 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 might help lessen these changes by constantly refreshing each room’s supply of air.