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As the temperature rises outside, you automatically reach for the thermostat to switch from heating to cooling. Your hand hovers over the second setting option. Should you set the fan to “Auto” or “On?” This question trips you up every season, and you eventually settle on your gut instinct.

This summer, you don’t have to play the guessing game anymore. We’re here to settle the age-old battle of whether your air conditioner fan should be set to the auto or on setting. First, you need to understand what the fan does.

What Does the Fan Do?

Your HVAC system’s fan is responsible for pulling in air to be heated or cooled and sending the air back through the vents in your house. The airflow you feel blasting out of the vent is created by the fan. You can switch the fan back and forth from the on and auto settings.

When the fan is set to the auto setting, the fan will only turn on when your system is cooling the air. When it’s set to the on setting, the fan will constantly run, even if the air conditioning unit is not actively cooling the air.

The Pros and Cons of Setting Your Thermostat to “Auto”

Whether you set your AC’s fan to “auto” or “on” is a personal preference. To help you make this decision wisely, we’ve presented the pros and cons of each setting below. Let’s take a look at the advantages and disadvantages of the auto setting first:


  • Lower Energy Consumption: When your thermostat is set to “auto,” the fan will only run when the air conditioner is actively cooling the air. This means less energy is used, and you can see significant savings overall.
  • Longer Lasting Air Filters: Since air is not constantly circulating through the air filters, they are less likely to clog. You will likely be able to get away with changing the filters every other month, as opposed to every month.
  • Less Wear and Tear on AC Parts: When the fan doesn’t run continuously, the motor and other fan parts are used less and have a better chance of lasting longer.
  • Better Dehumidification: With your AC fan set to auto, moisture built up from the cooling coils has a chance to drip and drain outside. If the fan runs constantly, moisture accumulates faster than the system can let it drain. This means the moisture can be circulated back into your house, raising the indoor humidity levels.


  • No Air Circulation Between Cycles: When the auto setting is turned on, you may notice that the air feels stagnant or stuffy between cycles.
  • Greater Fan Wear and Tear: Another thing you need to consider is that the constant on and off cycling of the system can cause the fan to wear out faster.

The Pros and Cons of Setting Your Thermostat to “On”

With your AC fan set to “on,” the fan will run every minute of every day. Here are the pros and cons of choosing this option:


  • Even Distribution of Cool Air: When the fan runs constantly, you will notice that the air throughout your home is more evenly distributed. You are less likely to struggle with cold or hot spots.
  • Better Air Filtration: With the fan continuously moving, the air is frequently pulled through the system’s air filter. In this way, more allergens are removed from the air, providing additional relief for those suffering from allergies.


  • Increased Costs: Letting your AC fan run constantly is certainly not the most energy-efficient option. The longer it runs, the more energy it will use. You will notice a significant difference in energy costs between the “on” and “auto” settings.
  • Uses More Air Filters: When the “on” setting is selected, you will notice that you have to change the filter more often since air is constantly circulated through it.

Go With the “Smart” Option

If you would like to save even more money, consider installing a smart thermostat. These modern thermostats offer a fan setting called “circulate,” which causes the fan to run during system cycles and for a few minutes every hour. With this setting, your air circulation will be better, and it will not cost you an arm and a leg! Plus, you can change the cooling and heating settings from anywhere when you have a smart thermostat, giving you more control over your energy bills.

Have Questions About Your Thermostat or AC? We Can Help!

At Northern Services, our technicians are committed to helping you feel comfortable in your home all summer long. We’ll keep your HVAC system running efficiently with AC maintenance in Renville County. And if your system starts acting up, we can provide timely air conditioner repairs. Contact us today to schedule a service appointment or ask additional questions!