This Thermostat Setting Will Leave Your Home Miserably Humid

Most homeowners don’t realize that your air conditioner actually has two responsibilities: to cool and dehumidify your home.

But if you’re leaving your thermostat fan setting to “ON”, you prevent your AC from removing as much moisture from your home.

And humidity inside your home isn’t just uncomfortable, it can cause damage and even make your family sick.

Let’s take a look at how this thermostat setting increases humidity and what setting you should be using instead.

How leaving your AC fan “ON” increases humidity

First off, it’s helpful to know the two settings for your AC fan and the difference between them:

  • AUTO—This setting runs your fan only when your AC is blowing cold air. In between cooling cycles, the fan shuts off.
  • ON—This setting runs your fan constantly, even when your AC isn’t actively producing cool air.

Setting your fan to AUTO instead of ON better dehumidifies your home.


Think of how a glass of ice water beads up and “sweats” when you place it in the sun. This is how your AC unit works.

Your AC’s refrigerant coils absorb heat and moisture from the air inside your home. That cold air is then blown into your home but the moisture is left behind sitting on the coils. 

And what happens to that moisture next depends on the setting of your fan.

If your fan is set to AUTO, it shuts off between cooling cycles. This allows time for the moisture on the cooling coils to collect and drain outdoors like it is designed to do. 

But if your fan is set to ON, the fan runs continuously and blows the moisture right back into your house. 

High humidity levels: the perfect conditions for mold

Although low humidity levels are often associated with comfort, it also serves a higher purpose and protects your family from health hazards such as mold.

The Department of Health and Human Services states that around 70% humidity or higher is the perfect breeding conditions for mold. 

Mold can cause breathing problems, skin irritations and a variety of other health concerns.

Leaving your AC fan set to ON allows the moisture in your home to accumulate and reach mold-growing levels of humidity.

To ensure that you and your family stay cool and healthy this summer, keep your AC thermostat fan setting to AUTO.

Professional HVAC Help

Coolray is your Atlanta and Birmingham area home comfort expert with specialists in heating, air conditioning, air quality, plumbing, and electrical. Have more questions? We’d be happy to help – just contact us online.

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