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

October 05, 2022

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

Most thermostats have a ‘Fan’ or ‘Fan On’ setting. But if the fan is on during a typical cycle, what will the fan setting provide for an HVAC system? This guide can help. We’ll walk through just what the fan setting is and whether you can use it to save money over the summer or winter.

What Is the Fan Setting on My Thermostat?

For the bulk of thermostats, the fan setting indicates that the HVAC blower fan remains on. Certain furnaces can operate 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 switch it off when the cycle is finished.

There are advantages and disadvantages to trying the fan setting on your thermostat, and whether you do or don’t will depend on your personal comfort requirements.

Advantages to switching to the Fan/On setting:

  • You can keep the temperature in every room more consistent by enabling the fan to keep circulating air.
  • Indoor air quality should improve as constant airflow will keep moving airborne particles through the air filter.
  • A smaller number of start-stop cycles for the blower fan helps expand its life span. Because the air handler is usually a component of the furnace, this means you can minimize the risk of needing furnace repair.

Drawbacks to utilizing the Fan/On setting:

  • A constant fan could add to your energy expenses somewhat.
  • Continuous airflow can 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 can 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, forcing the HVAC system to work more to keep up with the preferred temperature. In severe heat, this can result in needing AC repair more regularly as wear and tear increases.

The reverse can occur over the winter. Cooler spaces like a basement will hold onto cooler air, which can 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 remain warm.

If you’re still trying to decide 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 might work for you if:

Someone in your household suffers from 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 deals with hot and cold spots. All kinds of homes wrestle with stubborn hot and cold spots that quickly shift to a temperature different from the rest of the house. The fan setting should help minimize these changes by consistently refreshing each room’s ventilation.