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

October 05, 2022

When the weather is cooling off, you may be thinking about how you’ll prepare your heating and cooling. After all, HVAC bills can make up a big piece of your monthly electric bill. To learn new ways to lower their HVAC bill, some people take a closer look at their thermostat. Is there a setting they can use to increase efficiency?

The bulk of thermostats come with a ‘Fan’ or ‘Fan On’ setting. But if the fan is running during a normal cycle, what can the fan setting provide for your HVAC system? This guide will help. We’ll walk through what exactly the fan setting is and when you can use it to save money in the summer or winter.

What Is the Fan Setting on My Thermostat?

For most thermostats, the fan setting signifies that the HVAC blower fan keeps running. A few furnaces may continue to operate at a low level with this setting, but for the most part heating or cooling isn’t being produced. The ‘Auto’ setting, conversely, will turn on the fan during a heating or cooling cycle and turn it off when the cycle is complete.

There are benefits and drawbacks to switching on the fan setting on your thermostat, and whether you do or don’t should depend on your distinct comfort preferences.

Advantages to switching to the Fan/On setting:

  • You can keep the temperature throughout your home more uniform by permitting the fan to keep circulating air.
  • Indoor air quality will be highest as steady airflow will keep passing airborne pollutants into the air filter.
  • A smaller number of start-stop cycles for the HVAC fan helps extend its life span. Since the air handler is typically part of the furnace, this means you could avoid needing furnace repair.

Drawbacks to using the Fan/On setting:

  • A nonstop fan can raise your energy costs slightly.
  • Continuous airflow may 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

Through the summer, warm air will sometimes persist in unfinished spaces such as the attic or an attached garage. If you leave the fan on, your HVAC system might draw this warm air into the rest of your home, pushing the HVAC system to run longer to preserve the desired temperature. In serious heat, this may lead to needing AC repair more quickly as wear and tear gets worse.

The reverse can take place in 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 draw more cold air upward, increasing the amount of heating you need to remain warm.

If you’re still trying to figure out if you should use the fan/on setting, remember that every home and family’s comfort needs are different. Leaving the HVAC system’s fan on might be best for you if:

Someone in your household has allergies. Allergies and other respiratory conditions can be stressful 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. Many homes deal with difficult hot and cold spots that quickly evolve to a temperature different from the rest of the house. The fan setting might help lessen these changes by steadily refreshing each room’s supply of air.