eli5: If hot air rises and cool air falls, why are we told to have our ceiling fans blow up in the winter and down in the summer? Wouldn’t it make more sense to pull the air in the opposite direction it naturally goes to help it circulate?
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Air that’s close to the same temperature mixes readily — it makes no difference if you make the fan blow up or down.
Or rather, the only difference is whether you want to feel the breeze directly on you or not
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It also depends on whether you have your vents coming from the floor (as I have noticed up north) or the ceiling (like I often see down south).
Pro tip, clean your fan before you flip the switch. U don’t want all that accumulated dust to go everywhere
Ever had a fan blowing cold air directly on to you in winter? That’s why.
I would submit that running the fan in “winter mode” is actually an effective way to cool you in the summer. As stated in previous posts, it forces the air up, across the ceiling and down the walls. Most people put their furniture against the walls, so you get the breeze you want throughout the room without having to be directly under the fan. Run it at higher speeds in summer to get a breeze, and lower speeds in winter to circulate the warmer air from the ceiling. You can also benefit from the Bernoulli effect at any time of year, making you HVAC more efficient.
Amazed that people
A: didn’t know fans could change direction, and
B: were so wrapped up in the idea that the density of air changes at different temperatures, someone needed to explain that a breeze feels good when it’s hot but not when it’s cold.
Fans are very good at pushing air, but very bad a pulling air (unless there is some kind of enclosure). Put a balloon one meter in front of a fan and one meter behind it and you’ll see what i mean.
So you turn your fan on blowing up in the winter to push the hot air up there around the rest of the room.
In the summer, you want the fan blowing on you to help with evaporative cooling, aka sweat.
Also, within a minute or so of turning the fan on, you’re moving enough air to effectively eliminate the variation between the ceiling and the floor. The higher the fan speed, the more effective this mixing effect becomes. Ceilings typically have few obstacles to air flow than floors, so “winter mode” achieves a more effective circulation effect.
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