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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When you’re hot you sweat, even a little bit. THe air blowing on your skin feel cool. In the winter you want the cool air lifted off the ground and the hot air pushed down to the ground wo having a breeze directly on you.
The air coming down blowing on you on you feels cooler in summer, and reversing in winter draws cool air up which pushes warm air out and down as it’s displaced by cooler air being forced up.
I didn’t even know fan blades were supposed to be swapped seasonally so I’ve already learned something new.
It’s the difference between being in a room where a fan is circulating the air and sitting directly in front of the fan. Sitting in front of it will have a cooling effect you don’t want in winter.
In the summer, it’s not the circulation you want, it’s the breeze, you want the air blowing down on your skin to evaporate your sweat and cool your body. A fan literally does nothing to cool a room (actually it heats it up) if you’re not under the fan getting directly blowed on.
In the winter you *don’t* want the breeze (because you’re already cold) you want that hot air to come down off the ceiling back to the level you’re walking around in. So the fans blow up, so there is no breeze, but that upwards flowing air *pushes away* the warm air at the ceiling. The air moves until it hits a wall then flows down the wall to the floor. So in the winter the upwards blowing fan circulates the air to bring the warm air down to you.
EDIT – since this is blowing up a bit, if you look at your ceiling fan you’ll see what is typically a black two-position toggle switch. That’s the switch you flip that reverses the blade spin from summer to winter back to summer modes.
EDIT 2 – to be triple clear, if you leave a fan in “winter mode” and use the fan in the summer, you are literally making the room hotter and getting none of the breeze benefit of the fan. You are literally making the situation worse by running a fan in winter mode in the summer.
EDIT 3 – because I worded Edited 2 Poorly – the fan motor itself produces negligible heat. I’m didn’t mean to imply that the winter mode-in summer thing made the room hotter via the fan motor. I meant to state that winter mode in summer will just circulate down the hottest summer air down from the room’s ceiling and bring it down to human level. Considering you’re running the fan because you already feel too hot, bringing down the hottest air in the room to you, but also doing it slowly enough that you don’t get any nice breeze from it, it’s a poor choice.
EDIT 4 – Oh, ok, so final edit. A good number of people have challenged my 2nd and 3rd edits (in a surprisingly constructive & polite way, yay!). So, *I think I’m still right*, but whatever, who the hell am I? I could be totally wrong! I’m in construction, not a doctor of thermodynamics. That being said there are some great “You’re wrong because ….” below that are worth reviewing for debate’s sake.
In the winter, the warm air in the room “pools” around the ceiling. The air dragged up from a ceiling fan in winter mode pushes the warm air away from the ceiling and gets it to circulate back into the rest of the room where you can feel it.
I like the people that mention that a fan only cools you if it is blowing air at you, and technically warms the room (slightly). Throughout my life I’ve stood aghast at people who insist they need to leave their fan running while they are gone, cuz the room will be cooler (somehow?) when they return.
In the winter, the ceiling fan blows warm air down from the ceiling (where it would tend to stratify.)
In the summer, it doesn’t matter which direction the air blows, you just need air movement on your skin to help cool down by evaporating sweat.
Fans don’t cool by moving cool air down to you. They cool by moving air across you body. The difference in air temp between you and the fan is going to be pretty small.
Wait, there are ceiling fans that have the option to blow in both directions?… Today I learned a new thing
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