When the weather starts to cool off, you might be wondering about how you’ll make the most of your heating and cooling. After all, HVAC expenses routinely make up a significant portion of your monthly electric bill. To try and find ways to lower their HVAC bill, some people take a closer look at their thermostat. Could there be a setting they can use to improve efficiency?

Most 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 should help. We’ll walk through precisely what the fan setting is and how you can use it to reduce costs in the summer or winter.

What Is the Fan Setting on My Thermostat?

For the bulk of thermostats, the fan setting indicates that the system's blower fan remains on. A few furnaces will operate at a low level with this setting, but for the most part heating or cooling isn’t being made. The ‘Auto’ setting, in contrast, will start the fan during a heating or cooling cycle and switch it off once the cycle is over.

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

Advantages to switching to the Fan/On setting:

  • You can keep the temperature in every room more uniform by allowing the fan to keep circulating air.
  • Indoor air quality will be highest since continuous airflow will keep passing airborne pollutants into the air filter.
  • Fewer start-stop cycles for the system's fan helps extend its life span. As the air handler is typically part of the furnace, this means you might prevent the need for furnace repair.

Drawbacks to switching to the Fan/On setting:

  • A continuous fan could add to your energy costs slightly.
  • Nonstop airflow could clog your air filter in a shorter amount of time, increasing the frequency you’ll need to replace it.

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

During the summer, warm air will sometimes stick around in unfinished spaces including the attic or an attached garage. If you use the fan setting, your HVAC system may draw this warm air into the rest of your home, forcing the HVAC system to run longer to keep up with the set temperature. In serious heat, this could result in needing AC repair more quickly as wear and tear grows.

The opposite can happen over the winter. Cooler spaces like a basement will hold onto cooler air, which may eventually drift into the rest of your home. Keeping the fan on could pull more cold air upward, increasing the amount of heating you need to stay warm.

If you’re still trying to decide if you should try the fan/on setting, remember that every home and family’s comfort needs will vary. Leaving the HVAC system’s fan on could work for you if:

Someone in your household has allergies. Allergies and similar 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 has hot and cold spots. Many homes deal with stubborn hot and cold spots that quickly shift to a temperature different from the rest of the house. The fan setting might help limit these changes by consistently refreshing each room’s ventilation.