Most thermostat settings are easy to understand, with the main options being “heat” or “cool.”  But do you know the difference between the thermostat fan settings? To make the right choice for your home, it’s important to understand the differences between each setting and their benefits and disadvantages.

“On” Setting

This setting keeps your thermostat fan running at all times, even when your heating or cooling system is not on.


  • Keeps the air in your home moving through your furnace filter leading to better indoor air quality
  • Helps to better distribute warm or cool air
  • Your furnace fan is subjected to less wear and tear from constantly cycling on and off


  • Uses more energy, can lead to costs up to an extra $50 per year
  • Requires more frequent filter replacements
  • Can be noisy to have the fan running 24/7

“Auto” setting

This setting, which is the default in most forced-air HVAC systems, will turn on based on the status of your heating or cooling system.  When the heat is on, the fan will only turn on as your home heats up. When cooling, the fan will only run while your air conditioner is running.


  • Helps save on energy costs, since the fan isn’t running constantly
  • Furnace filters will need to be replaced less often


  • Will not distribute conditioned air as evenly once the temperature has reached the desired setting
  • May lead to higher maintenance costs since having the fan repeatedly turning on and off can lead to more wear and tear

Some thermostats now offer a “Circulate” setting that will turn your fan on for a set period of time to help in circulating the air. Many modern HVAC systems now come with variable-speed blower motors that provide similar benefits to running your thermostat fan on “on.” The whole heating or cooling system adapts its running speed to your temperature demands, and usually runs at a slower, more continuous speed.

To learn more about furnace settings or to speak with one of our professionals, contact us at Mowery Heating, Cooling and Plumbing, proudly providing superior service in the Greater Indianapolis area.

Our goal is to help educate our customers in Brownsburg, Indiana and surrounding areas about energy and home comfort issues (specific to HVAC systems).