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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. Does having a thermastat with a humidify component more efficient on your air conditioner. What is the benefit of having a humidistat on your AC

  2. If you leave the setting on auto and then shut it off when you leave the home all day for work isnt that better than to leave it on auto all day? For those 8 hours???? What about compiters. Should they be unplugged?

  3. What is the difference between having a ceiling fan rotate clockwise versus counterclockwise? I note that your advice was to have it rotate counterclockwise but it feels breezier when going clockwise

  4. I am really pleased with FPL . You are definitely making the effort to educate customers on energy usage .
    I am impressed . Keep up the good work

  5. W


  6. I have a neighbor who insists on turning her a/c off during the day. When she comes home she turns it back on. I leave mine on all day but set the thermostat at 77° and my monthly bill is less than hers. I’ve tried to explain to my neighbor it costs more to recool the house, thus using more electric. Who’s right and who’s wrong? Thanks for your help.

  7. I changed my lights for Philips hue and I’m saving about $50 per month.

  8. For the last year I have been using the averaging idea. My bill is higher than it was before. Particularly the last two billing cycles. I was gone for two weeks in September, the thermostat was set at 85 and yet my bill is 20.00 higher than the previous month. No one was in the house for those two weeks except to check on my cats. No electrical use except pool filter. Why has it increased In August and September?

    • I live in a 900 sq ft condo. When I leave for the summer I keep my thermostat set at 78. What is the correct setting I see some people keep there’s at 85

    • I have the same issue with this “budget billing” idea. I thought it would be cheaper, but somehow keeping the same temperature in my house, even from prior to joining the program, my bill continues to increase by 20 dollars per month. This month the hurricane hit and did not have power for 4 days. Any compensation by FPL not at all. I am thinking about discontinuing the budget billing. Let me know if you did and what happened.

  9. I just received this months online bill. I was shock to see the increase of $33.00 than the last month. I leave the temperature to 83 deg all day. I am not home most of the time and at night I use the fan in the bedroom. I live alone and on fixed income. Please explain where I went wrong or maybe miscalculation on your part. Thank you.

  10. Just signed up for the auto payment from my personal bank account. Please send the restaurant discount certificate.
    Thank you,


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