24/7 Emergency Support

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

October 05, 2022

Once the weather starts to cool off, you might be concerned about how you’ll prepare your heating and cooling. After all, HVAC expenses routinely make up a significant piece of your monthly electric bill. To learn new ways to reduce costs, some owners look closer at their thermostat. Is there a setting they could use to increase efficiency?

The bulk of thermostats include both a ‘Fan’ or ‘Fan On’ setting. But if the fan is running during a normal cycle, what does the fan setting provide for the HVAC system? This guide should help. We’ll review what exactly the fan setting is and when you can use it to reduce costs over 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. A few furnaces can run at a low level in this setting, but in most cases heating or cooling isn’t being made. The ‘Auto’ setting, conversely, will turn on the fan during a heating or cooling cycle and turn it off after the cycle is over.

There are benefits and drawbacks to using the fan setting on your thermostat, and the ideal option should depend on your personal comfort needs.

Advantages to using the Fan/On setting:

  • You can keep the temperature in each room more uniform by allowing the fan to keep circulating air.
  • Indoor air quality can increase because continuous airflow will keep moving airborne particles into the air filter.
  • Fewer start-stop cycles for the system's fan helps extend its life span. As the air handler is usually connected to the furnace, this means you can prevent the need for furnace repair.

Drawbacks to switching to the Fan/On setting:

  • A continuous fan could increase your energy costs slightly.
  • Nonstop airflow can clog your air filter up more quickly, increasing the frequency you will want to replace it.

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

During the summer, warm air will sometimes linger in unfinished spaces like 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 run longer to keep up with the preferred temperature. In severe heat, this can lead to needing AC repair more regularly as wear and tear increases.

The opposite can occur over the winter. Cooler spaces like a basement will hold onto cooler air, which can eventually flow into the rest of your home. Leaving the fan setting on could pump more cold air upward, increasing the amount of heating you need to keep warm.

If you’re still trying to determine if you should switch to the fan/on setting, keep in mind that every home and family’s comfort needs are not the same. Leaving the HVAC system’s fan on could be best for you if:

Someone in your household suffers from allergies. Allergies and other respiratory conditions can be stressful on the family. Leaving the fan on can help to improve indoor air quality, helping your family breathe easier.

Your home deals with hot and cold spots. Lots 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 lessen these changes by constantly refreshing each room’s airflow.