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A/C fan “on” or “auto?” Which uses less energy?

A/C fan “on” or “auto?” Which uses less energy?

by | Aug 30, 2016 | 239 comments

I’m hoping you can help settle a bet. A friend of mine thinks leaving her A/C fan setting on “auto” uses more energy. Which A/C fan setting actually costs more – “on” or “auto?”

Asked by: Victoria I., Port St. Lucie

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Hi Victoria, that’s a great question, and I’m happy to give you the facts to share with your friend. First of all, it’s important to understand that the on/auto fan switch on your A/C thermostat will affect the price you pay to cool your home. That’s because the A/C fan circulates the cool or warm air throughout your home. Switching the fan to “on” will make the A/C fan run continuously – all day long. If you choose the “auto” setting, this will allow the fan to shut off with the rest of the cooling system as soon as your desired temperature is reached.

Fan “on” costs more
Advice from friends can be helpful, but in this case your friend was mistaken to think that the “auto” setting used more energy. Let’s assume your air conditioner normally cycles off 30 percent of the time. In this example, turning the fan switch to “on” will make the fan run over 200 extra hours a month. For a typical size central air conditioner, that would cost you about $8 more each month. Keep in mind, a fan that runs all the time may wear out sooner.

Another reason to keep it on “auto”
Setting your A/C fan to “auto” also helps provide better dehumidification. Have you noticed how moisture from the air condenses on the outside of a cold drink on a humid day? Your A/C unit captures moisture the same way, helping your home feel more comfortable. When the fan cycles off using the “auto” mode, moisture has a chance to drip from the cold cooling coils into the condensation pan and then drain outside. However, when the fan runs all the time in the “on” setting, less moisture has a chance to drip and drain outside. Some people prefer the feel or sound of the fan running all the time. If that’s you, at least now you know how much that choice will cost you.

Learn how to save even more
At FPL, we’re always working to help you keep your energy bills low and find you new ways to save. Visit our summer tips page for more ways to control your energy costs. Remember, you can save five percent on your monthly cooling costs for each degree you turn your thermostat up.

Don’t forget, you can also take our Online Home Energy Survey to get a personalized savings plan filled with energy-saving tips and recommendations. It’s easy – with just a few clicks you can save up to $250 a year.

About The Author

Tiffany Spence

Tiffany Spence is an energy expert at Florida Power & Light Company. She's conducted thousands of energy audits at homes and businesses, helping customers find new ways to make their bills even lower.


  1. I am wondering why FPL does not offer or have offered any kind of incentive for people in Florida to buy whole house fans. (used to be called attic fans) Starting in Oct the evening weather cools down and these fans are GREAT for drawing in the cooler night air so we don’t have to use our A/C.

  2. no comment

  3. Very interesting,now I will check more for info !
    Thank you

  4. I am a snow bird I guess. I have to say whenever I have a problem u guys r great. Thank u for great service.

  5. My condominium is going to switch lights (quantity 70). I argue that we should switch to LED vs incandescent. Can you make the argument for me?


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