Quirks & Quarks

Why do fans make the air feel cooler?

Air flow from a fan makes the air feel cooler due to convection and evaporation

Air flow from a fan makes the air feel cooler due to convection and evaporation

The increase in velocity of air flow from a fan makes the air, and you, feel cooler (Shutterstock / Ben Bryant)

This week's question comes from Scott Leggo in Corner Brook, Newfoundland and Labrador. He asks:

Why does air from a fan feel cooler than air going into a fan?

Fatima Suleiman, a PhD candidate in the Department of Mechanical and Mechatronics Engineering at The University of Waterloo, says a fan doesn't reduce the temperature of the air exiting or downstream of the fan.

The increase in velocity of the air flow from the fan that causes the air to feel cooler than the air going into the fan. The fast moving air increases the rate at which our bodies lose heat due to convection and evaporation. 

The faster moving air from the fan displaces the warmer air that is in direct contact with our skin. This enhances the rate of convective heat transfer, which means we feel cooler. 

Moisture in the form of sweat on our skin also evaporates more quickly in the presence of fast moving air. This takes away some body heat and makes us feel cooler.

In a similar way, blowing on hot food cools it down faster than having it sit in air of the same temperature. 

Produced and written by Mark Crawley

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