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

October 05, 2022

When the weather starts to cool off, you may be thinking about how you’ll make the most of your heating and cooling. After all, HVAC bills frequently add up to a significant portion of your monthly electric bill. To figure out new ways to lower their HVAC bill, some people look closer at their thermostat. Maybe there’s a setting they can use to boost efficiency?

The majority of thermostats come with a ‘Fan’ or ‘Fan On’ setting. But if the fan is on during a regular cycle, what can the fan setting provide for your HVAC system? This guide should help. We’ll review precisely what the fan setting is and how you can use it to save money in the summer or winter.

What Is the Fan Setting on My Thermostat?

For the majority of thermostats, the fan setting signifies that the system's blower fan remains on. Some furnaces can generate heat at a low level with this setting, but in most cases heating or cooling isn’t being made. The ‘Auto’ setting, conversely, will start the fan over a heating or cooling cycle and turn it off when the cycle is over.

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

Advantages to utilizing the Fan/On setting:

  • You can keep the temperature throughout your home more consistent by allowing the fan to keep circulating air.
  • Indoor air quality should improve because continuous airflow will keep forcing airborne pollutants through the air filter.
  • Fewer start-stop cycles for the system's fan helps extend its life span. Since the air handler is typically part of the furnace, this means you can avoid needing furnace repair.

Disadvantages to using the Fan/On setting:

  • A nonstop fan will likely raise your energy expenses by a small margin.
  • Constant airflow could clog your air filter in a shorter amount of time, 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 linger in unfinished spaces such as the attic or an attached garage. If you use the fan setting, your HVAC system can draw this warm air into the rest of your home, pushing the HVAC system to run longer to preserve the preferred temperature. In serious heat, this may result in needing AC repair more often as wear and tear grows.

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

If you’re still trying to decide if you should try 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 may work for you if:

Someone in your household suffers from allergies. Allergies and similar respiratory conditions can be hard 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. Many homes wrestle with difficult hot and cold spots that quickly evolve to a temperature different from the rest of the house. The fan setting might help limit these changes by constantly refreshing each room’s supply of air.