Confused by which AC fan setting to use?
We recommend that you set your thermostat to AUTO instead of ON.
In this blog, we’ll explain:
- The difference between the AUTO and ON settings
- Why you should normally set your thermostat to AUTO
- When to use the ON setting
Let’s start by looking at the difference between both fan settings.
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The difference between the AUTO and ON settings
Both the AUTO and ON settings control the AC blower fan, which is located in the air handler (the indoor part of your AC system). The blower fan pulls warm air into the AC to be cooled, then blows the cool air back into your home.
The blower fan is located in the indoor AC unit
When you select the:
- AUTO setting, it means the fan will only turn on when your system is cooling air
- ON setting, the fan will run non-stop—even if your AC isn’t actively cooling your home’s air
Now that you know the difference between the two fan settings, let’s look at why you should normally leave your thermostat set to AUTO.
Why you should normally set your thermostat to AUTO
Compared to the ON setting, the AUTO setting gives you benefits such as:
- Lower energy consumption. In AUTO mode, the blower fan only runs when necessary, which cuts down your AC system’s energy usage.
- Reduced wear and tear on AC components. Because the fan isn’t running constantly, the motor and other fan components will last longer.
- Better dehumidification. In AUTO mode, the fan shuts off between cooling cycles. This allows more moisture from humid air inside your home to collect and drain outside, which leads to lower indoor humidity.
Less noise. Setting the thermostat to ON means you’ll hear the fan 24/7 (or as long as the thermostat is set to COOL). In AUTO mode, you’ll only hear the fan as it’s pushing cool air into your home. If you have a newer high-efficiency system, this will not apply to you as the fan noise is minimal in newer systems anyway.
When to use the ON setting
In the following situations, it may be necessary or beneficial to use the ON setting:
- You’re cleaning your house. If you’re dusting or vacuuming your home, setting the thermostat fan setting to ON can actually help you clean. The ON setting improves air circulation, which means airborne particles like dust will be pulled into your air filter. Set your thermostat to ON while cleaning, and leave it on 15-30 minutes afterward. Then, switch your thermostat back to AUTO.
- You’re hosting a lot of guests. Sometimes the air can feel stuffy when there are a lot of people in a confined space. Turning the thermostat fan setting to ON can help circulate fresh air, making the room feel more comfortable.
Have more thermostat questions?
We’re happy to answer any questions you may have. If your thermostat or AC system is giving you problems, we also offer same-day AC repairs.