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

October 05, 2022

As the weather begins to cool off, you are probably wondering about how you’ll make the most of your heating and cooling. After all, HVAC costs can make up a significant portion of your monthly electric bill. To figure out new ways to lower their HVAC bill, some homeowners look closely at their thermostat. Is there a setting they should use to boost efficiency?

The majority of thermostats come with a ‘Fan’ or ‘Fan On’ setting. But if the fan is on during a normal cycle, what does the fan setting provide for your HVAC system? This guide can help. We’ll review precisely what the fan setting is and how you can use it to cut 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. Some 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 run the fan during a heating or cooling cycle and shut it off once the cycle is finished.

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

Advantages to utilizing the Fan/On setting:

  • You can keep the temperature in each room more consistent by permitting the fan to keep generating airflow.
  • Indoor air quality can increase because steady airflow will keep forcing airborne contaminants through the air filter.
  • A smaller amount of start-stop cycles for the HVAC fan helps lengthen its life span. Since the air handler is usually connected to the furnace, this means you can prevent the need for furnace repair.

Drawbacks to using the Fan/On setting:

  • A constant fan can add to your energy costs slightly.
  • Constant 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 may persist in unfinished spaces such as the attic or an attached garage. If you use the fan setting, your HVAC system might draw this warm air into the rest of your home, compelling the HVAC system to work harder to maintain the desired temperature. In severe heat, this may lead to needing AC repair more quickly as wear and tear grows.

The opposite can happen over the winter. Cooler spaces such as a basement will hold onto cooler air, which can eventually make its way into the rest of your home. Leaving the fan running may pull more cold air upward, increasing the amount of heating you need to keep warm.

If you’re still trying to figure out if you should try the fan/on setting, don’t forget that every home and family’s comfort needs are different. Leaving the HVAC system’s fan on might be ideal for you if:

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

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