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From Constellation Energy

Quick energy efficiency tip: To stay cool and manage your energy at the same time, use ceiling fans to create a “wind chill” in rooms you are using. The wind chill will help you feel cooler than the actual temperature. Make sure the ceiling fan is set to turn in a counter-clockwise rotation.

I was wondering why the ceiling fan is set to turn in a counter-clockwise rotation, instead of the other way around?

Thanks!

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    $\begingroup$ Most ceiling fans have a reverse switch, which makes the blades spin the other way so the fan blows air towards the ceiling. I believe the purpose of this is to circulate air without producing a strong cooling feeling. The only silly thing about this statement is that it is unclear because it relies on the assumption that all fans have their blades angled the same way. This is likely a good assumption, but it is still a confusing way to say "make sure the fan is blowing downwards". $\endgroup$
    – Colin K
    Jul 17, 2012 at 12:01
  • $\begingroup$ @DImension10 Abhimanyu PS : Please stop removing the fan tag. The benefit thereof is too small compared with the noise it creates on the front page. $\endgroup$
    – Qmechanic ♦
    Sep 30, 2013 at 8:44

3 Answers 3

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The blades of a ceiling fan are pitched out of plane slightly. As a result, when the fan spins, the blades push air either up towards the ceiling or down towards the floor. Which direction it pushes air is determined by the direction the fan is spinning, and the direction the blades are pitched. The usual convention is given by the right hand rule: if you hold your right hand so that you can curl your fingers in the direction the fan is spinning, then it will push air in the direction that your thumb is pointing.1 When it's pushing air down on you, it will then be spinning in a counter clockwise direction as you look up at it. You can make it follow a left hand rule by reversing the pitch of the blades.

Once you have set the direction of the pitch of the blades, you can reverse the airflow by reversing the direction the fan spins. Many (most?) modern ceiling fans provide some mechanism to do this. The fans in my house have a small black switch that slides up and down. @Ignacio Vazquez-Abreams mentions using a pull chain in a comment to another answer.

In warm weather, you set the fan so that it pushes air down towards the floor. This causes you to feel a breeze, which cools you. In cold weather, you set the fan so that it pushes air up into the ceiling. You don't feel a breeze,2 but it circulates warm air from the ceiling towards the walls and down towards the floor.

  1. Box fans usually follow the right hand rule as well. You may find it easier to check some of this if you have a box fan handy. You can walk around the fan and hold a tissue in front of it from both side while watching the blades spin.
  2. You can check this with a box fan. Set the box fan on the floor, and turn it on. It will pull air from one side and push it out the other. You feel a breeze on the "out" side and feel a much weaker breeze (if any) on the "in" side.
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If the fan rotates the wrong way it will blow the air up onto the ceiling, so at best you'll get a turbulent breeze as the air flows along the ceiling then down. It's obviously better that the fan blows the air straight down as you'll feel a higher air speed.

I agree with Ron that the comment from Constellation Energy seems rather silly, but the thought of people bolting their fans to the ceiling the wrong way up made me smile on a rainy Tuesday morning. Maybe if you ramped up the fan speed the updraft might exert an evolutionary effect by ridding the gene pool of people unable to read the instructions :-)

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    $\begingroup$ Ceiling fans can't be bolted the wrong way up. They can, however, have their "Reverse" chain pulled. Not really sure what effect that's supposed to have though, other than to make the air come down the walls instead of the center... $\endgroup$
    – Ignacio Vazquez-Abrams
    Jul 17, 2012 at 6:48
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It is not necessary that to push air down the fan must rotate counter clockwise. by adjusting the angular twist of the blade in the reverse manner the same can be achieved even by rotating the fan in the clockwise direction. the angular twist is to be so made that in which direction the fan rotor is rotating. at present the rotor is made rotate in the counterclockwise direction and the blades are made accordingly. i don't know the reason why the rotor is made to rotate in the counter clockwise direction, the answer for which i also visited this site.

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