There is an often cited statistic in the HVAC field that reversing the ceiling fan direction can save 10% on heating bills due to air circulation.

I would imagine that this is somewhat true due to the fan circulating the air.

In theory, reversing the fans direction should flip the intake (blows from high elevation to low elevation) and makes it blow from low elevation to high elevation.

Conceptually this doesn't make sense to me though. In the winter mode, the cold, higher density air appears to be taken through the fan blades and stay on the ceiling only to return down the sides of the walls (kind of like the magnetic field line shape).enter image description here

If the fan was in summer mode, wouldn't it make more sense to have the hot air pass down directly through the blades (where the warm air would be more concentrated) and warm the center of the room instead of the edges? Or is this for the entire house and not the benefit of any one person in the room?

Is there even any scientific evidence behind some of these claims, or is it mainly a marketing point?

  • 1
    As stated here. What Direction Should a Ceiling Fan Spin in Winter? Ceiling fans should rotate in a clockwise direction in winter, which will cause the fan to blow cold air towards the ceiling. Nov 21 at 19:31
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    It would be interesting to know how much of a thermal gradient actually occurs between floor and ceiling. Additionally, I too see no reason why reversing direction in a closed room would make a difference to just running normally in terms of breaking up that gradient.
    – Jack
    Nov 21 at 22:27
  • 1
    I am trying to get my head around the claim. Is it that blowing up in the winter will break up that thermal gradient that @Jack mentions, without focusing the airflow on people sitting under the fan, and thus avoiding an evaporative cooling effect.on their skin? If so, interesting claim. I look forward to seeing some evidence.
    – Oddthinking
    Nov 22 at 4:02
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    Are you claiming that you use less energy (ie: lower bill), or become more efficient (more air moved / joule)?
    – tuskiomi
    Nov 22 at 4:11
  • In order to make this a "notable" claim, it would be helpful to quote a source or, even better, a quantitative study that explains how exactly this is supposed to work.
    – Hilmar

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