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

October 05, 2022

As the weather starts to cool off, you might be thinking about how you’ll take full advantage of your heating and cooling. After all, HVAC expenses routinely contribute a significant portion of your monthly electric bill. To figure out new ways to save, some owners look closer 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 running during a typical cycle, what will the fan setting offer for the HVAC system? This guide will help. We’ll review just what the fan setting is and when you can use it to save money over the summer or winter.

What Is the Fan Setting on My Thermostat?

For the majority of thermostats, the fan setting indicates that the HVAC blower fan remains on. Certain furnaces may continue to run at a low level in this setting, but in most cases heating or cooling isn’t being made. The ‘Auto’ setting, on the other hand, will start the fan during a heating or cooling cycle and shut it off when the cycle is complete.

There are pros and cons to trying the fan setting on your thermostat, and the ideal option should depend on your unique comfort requirements.

Advantages to trying the Fan/On setting:

  • You can keep the temperature throughout your home more consistent by allowing the fan to keep running.
  • Indoor air quality can increase as constant airflow will keep moving airborne contaminants through the air filter.
  • Fewer start-stop cycles for the system's fan helps expand its life span. As the air handler is usually part of the furnace, this means you can avoid needing furnace repair.

Drawbacks to utilizing the Fan/On setting:

  • A continuous fan could raise your energy costs by a small margin.
  • 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

Through the summer, warm air may stick around in unfinished spaces including the attic or an attached garage. If you leave the fan on, your HVAC system may pull 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 can result in needing AC repair more often as wear and tear gets worse.

The reverse can take place during the winter. Cooler spaces such as a basement will hold onto cooler air, which will eventually make its way into the rest of your home. Keeping the fan on will sometimes draw 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 not the same. Leaving the HVAC system’s fan on may be ideal 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 should help to enhance indoor air quality, helping your family breathe easier.

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