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

October 05, 2022

When the weather begins to cool off, you may be wondering about how you’ll take full advantage of your heating and cooling. After all, HVAC costs can make up a significant chunk of your monthly electric bill. To learn new ways to lower their HVAC bill, some homeowners look closely at their thermostat. Maybe there’s a setting they should use to boost efficiency?

The majority of thermostats include both a ‘Fan’ or ‘Fan On’ setting. But if the fan is running during a normal cycle, what will the fan setting offer for your HVAC system? This guide should help. We’ll walk through what exactly 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 majority of thermostats, the fan setting means that the HVAC blower fan remains on. Some furnaces will run at a low level in this setting, but for the most part heating or cooling isn’t being produced. The ‘Auto’ setting, conversely, will start the fan over a heating or cooling cycle and switch it off once the cycle is over.

There are pros and cons to switching on the fan setting on your thermostat, and whether you do or don’t should depend on your unique comfort needs.

Advantages to trying the Fan/On setting:

  • You can keep the temperature in every room more consistent by allowing the fan to keep circulating air.
  • Indoor air quality will be highest as constant airflow will keep forcing airborne particles into the air filter.
  • Fewer start-stop cycles for the blower fan helps extend its life span. Because the air handler is often part of the furnace, this means you could prevent the need for furnace repair.

Disadvantages to utilizing the Fan/On setting:

  • A nonstop fan can raise your energy bills somewhat.
  • Continuous airflow can clog your air filter soon, increasing the frequency you will want to replace it.

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

In the summer, warm air will sometimes stick around in unfinished spaces like the attic or an attached garage. If you leave the fan on, your HVAC system can draw this warm air into the rest of your home, forcing the HVAC system to work harder to maintain the set temperature. In severe heat, this may lead to needing AC repair more quickly as wear and tear gets worse.

The opposite can happen during the winter. Cooler spaces like a basement will hold onto cooler air, which may eventually make its way into the rest of your home. Leaving the fan running may pump 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, remember that every home and family’s comfort needs are different. Leaving the HVAC system’s fan on may be best 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 can help to enhance indoor air quality, helping your family breathe easier.

Your home has hot and cold spots. All kinds of homes deal with stubborn hot and cold spots that quickly evolve to a temperature different from the rest of the house. The fan setting should help lessen these changes by constantly refreshing each room’s ventilation.