Does waving a fan really cool you down?

21 April 2015

Question

It seems to me that when people fan themselves in hot weather that the energy expended in waving the fan negates the cooling effect of the air movement? Is it not better to sit still?

Answer

We put this question to Naked Scientist Ginny Smith...

Ginny - I have used fans before. It certainly feels like it's cooling you down. I imagine it's helping your sweat to evaporate which is going to cause a cooling effect. I mean if you're holding one of those huge fans when you're fanning a queen, you know, those giant ones, I imagine that takes quite a lot of energy. But if it's a little sort of handheld foldout thing, I wouldn't have thought it takes too much energy to fan.

Chris - There is going to be an energy cost to moving the fan as you say. Muscles are only about 20 per cent efficient. So, of all the energy you use, actually moving the fan, 80 per cent of it is being wasted and turning into heat, exactly as Steven is suggesting. So, you've actually got to fan a bit harder and sweat a bit more to compensate for the fanning effect, but it will still cool you down because of evaporation. So, I think there's still a net benefit Steven, but it's going to be a modest one.

Kat - Absolutely fascinating stuff.

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