This is one of the most searched HVAC questions online. Should I set my thermostat fan to AUTO or ON? Your thermostat fan setting (either auto or on) controls the blower on your HVAC system. The blower is what helps push hot or cold air though the home until the air reaches the temperature on the thermostat setting.

What is the difference between Auto and ON?

AUTO means that the fan turns on automatically when your system is heating or cooling air. Once the thermostat reaches the desired temperature, the entire system shuts off until the next cycle.

ON means that the fan is constantly running and blowing air even when your HVAC system is not heating or cooling air.

Pros of AUTO setting

Keeping your fan on AUTO is the most energy-efficient option. The fan only runs when the system is on and not continuously. This means less energy bills.
Since auto shuts the fan on and off between cycles, the additional cycles of could shorten the life of the fan.

Cons of AUTO setting

It could cause hot/cold spots as the air isn’t delivered evenly throughout the home.

Pros of ON setting

The air quality in your home will be better if it is pulled through a filtration or UV light system because it will be cleaning the air continuously.
Air will be circulating continuously, which could feel more comfortable.
There could be reduced stress on the fan from less frequent starts and stops, which could potentially help extend its lifespan.
Temperature in the home is more consistent.
Fewer start/stop cycles on your AC fan (less wear and tear) = longer lifespan.

Cons of ON setting

You’ll need to replace your furnace filter more often as air is constantly being blown through it. The additional passage of air means more particulates will be trapped in the filter more often causing it to become dirty faster.
During the summer, any ducts that run in your attic or close to your outside walls can fill with warm air, blowing hot air into your home. Your HVAC system many now need to run more to offset the additional heat.
Higher energy bills due to continuous operation of the fan.
There is less dehumidification in the home during summer months. When your fan runs constantly, moisture from the coil doesn’t have a chance to drain outside and can disperse humidity into the home.

Ultimately, it’s your choice whether you set your thermostat to auto or on fan setting. If you have an air cleaner like a UV light, air scrubber or LED light then we would recommend settings the AC fan to “on” so that the air is continuously cleaned and circulated.

If you want to cut down on energy bills, “auto” may be the best option for you so you aren’t spending additional money running the fan.

Is comfort most important? Then “on” is your best choice so that air is distributed more evenly throughout the home.

Where do I find the AC fan setting on my thermostat?

If you have a more traditional thermostat that does not have a digital display, there should be a toggle switch or small knob that can be adjusted from auto to on. This switch is usually located right on the front of the thermostat. It can sometimes be on the side.

If you have a digitally based thermostat like an ecobee, nest, or the like, then you will need to go into the settings menu by touching the 3 little menu bars on the home display and finding fan settings from there. You may also be able to access these settings from your mobile app. Each thermostat is slightly different.

If you are in the Cincinnati area and would like an estimate on adding air cleaning solutions to your home, just book an estimate online or give us a call at 513.620.4822.