This is one of the most searched HVAC questions online. Should I set my AC fan on the thermostat 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 AC Fan Auto and ON setting?

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?

Homeowners can find their thermostat settings by locating their thermostat, which is typically mounted on a central wall in the home, such as in a hallway, living room, or near the HVAC system. Most smart thermostats have a digital display with labeled buttons or a touchscreen interface where you can navigate settings for temperature, fan control, and system mode. If you have a smart thermostat, you may also access settings through a mobile app. For older manual thermostats, look for a small switch or dial that controls the fan and system settings. If you’re unsure about your thermostat model, check the user manual or look up instructions online based on the brand and model number.

What is my Thermostat Display is Blank?

If your thermostat display is blank, it could indicate several issues. The most common reasons include:

Dead Batteries – If your thermostat is battery-powered, the batteries may need to be replaced. Try swapping them out with fresh ones.
Tripped Circuit Breaker – Your HVAC system may have tripped a breaker, cutting power to the thermostat. Check your electrical panel and reset any tripped breakers.
Loose or Disconnected Wiring – A loose or damaged wire inside the thermostat or HVAC system could cause a loss of power. If you’re comfortable, you can carefully check the wiring, but it’s best to have a professional inspect it.
Blown Fuse – Some HVAC systems have internal fuses that can blow, cutting power to the thermostat. This typically requires an HVAC technician to diagnose and replace.
Malfunctioning Thermostat – If the thermostat itself is faulty or old, it may need to be reset or replaced.

If replacing the batteries or resetting the breaker doesn’t work, it’s best to call a professional HVAC technician to diagnose and fix the issue.

Thermostat Services Cincinnati, OH

If you are in the Cincinnati area and need help with your thermostat don’t hesitate to give Quality Comfort a call at 513-620-4822 or book service online.