ON VS AUTO: Which Thermostat Setting Is Better?

Your air conditioner uses a fan to deliver the cold air it produces. You manage this fan at your thermostat by switching it to “auto,” which means the fan will only be on when the air conditioner is running. Or you can switch it to “on,” which indicates it will work continuously.

During the hot weather, operating your air conditioning can be your highest monthly utility expense. We are all looking for ways to save money. That may involve finding an energy-efficient AC setting or even upgrading to an ENERGY STAR®-rated unit with air conditioner installation.


What AUTO and ON mean

The fan setting controls your AC’s blower; a fan inside your system that helps distribute air throughout your home.

AUTO means the fan turns on “automatically” ONLY when your system is heating or cooling your air. When the thermostat reaches your temperature setting, the system, including the blower fan, shuts off. This is the most energy efficient option.

ON means the fan is CONSTANTLY blowing, even when your system isn’t working to heat or cool the air. We recommend avoiding the ON setting for several reasons.


Air Conditioner Fan Set to “Auto”

AUTO is short for automatic. The fan only turns on when cooling or heating is required.

If you are generally as comfortable in one room of your home as the next, you will want to use the AUTO setting. The AC fan kicks in when needed and stops running when the job is done.

This is the best energy-efficient setting, since the fan will only operate when your air conditioner does. It is ideal if your house always feels comfortable, regardless of which area you are in.


  • Saves energy and lowers your monthly energy bills.
  • Air filters may not need to be replaced as often.
  • Greater control over your system. You specify when the fan turns on (by temperature) and when it shuts off.


  • Conditioned air isn’t delivered evenly through your home, which can result in hot-and-cold spots.
  • The indoor air quality in your home may not be as clean and clear as it would in the ON setting.


Air Conditioner Fan Set to “On”

“On” means the fan is on  24/7, even when the air isn’t being heated or cooled. Having your air conditioner’s fan go all the time can better equalize your home’s comfort. This is good if you live in a two-story house, since areas upstairs can be warmer. It is also ideal if you struggle with unbalanced cooling because of hot and cold spots.


  • Keeps the air in the home consistent. Perhaps you want the cooler air in the basement and the hotter air in the upstairs bedrooms to be more balanced. A constant fan can help with this.
  • Indoor air is clean. Since air is always flowing through your home’s air filtration system, the air stays cleaner as long as you have a decently efficient filter and keep your windows closed.
  • Entended Lifespan. Fewer stop-and-start cycles for your AC fan which can help extend its lifespan.



  • Higher energy costs. Since the fan is always running, you’re using more energy than when the fan only runs when your system is heating or cooling.
  • Increases humidity. When the fan is set to “On” your AC will not dehumidify your home as well as it should. The air conditioning cycle continues to run as the indoor coil gets colder. Now water vapor (pulled from the air) begins to condense on the coil while passing over. If the compressor is turned off, the coil warms up. The water vapor on the coil will simply sit there until the next cycle, with some of it evaporating and sitting in the air inside the coil housing. But when the fan runs continuously, the air passing over the coil as it warms up evaporates that water and puts it right back into your house raising the humidity level overall.
  • Worsens air duct leakage. Most homes leak about 10% of the supply air and 12% of the return air through their duct system. So if the fan is blowing all the time, you’re always losing your conditioned air, running up your energy bills.
  • More frequent repairs. Obviously, when the fan runs constantly, it increases the wear and tear on your blower motor. This will lead to repairing and replacing worn parts or possibly the motor itself sooner than necessary.


Give Us a Call

Keeping your Southern California home cool during the scorching summer heat just got easier, with help from Aire-Tech! We give you countless resources to help you explore and learn about HVAC and energy efficient options for your home.

If your system needs repair or inspection, call Aire-Tech on 951-926-1002. You can also visit our Contact page and complete the contact form.