I recently saw a public service ad on TV that advised people to change the direction of rotation of their ceiling fans twice yearly, in winter and summer, and this would increase energy efficiency in the house. There’s a switch to make the fans change direction, but it’s not labeled clockwise/CCW or anything. Alas, the ad went by too fast for me to catch the instructions, but it raised a bigger puzzlement once I considered it.
Which direction is the fan supposed to rotate in summer, and which way in winter?
Just which way IS clockwise? Is it clockwise as I look at the fan from underneath? Or is it clockwise as I conceptually look at it from above?
I’ve read that fans are supposed to push hot air down in the winter, and pull cool air up in the summer. This makes sense, except for the fact that the air movement in the winter would seem to offset the benefits of several degree warmer air, and fans (ours, anyway) aren’t strong enough to pull a whole lot of air up…
ok on all or at least most cieling fans, there is a little switch. it decides which way the fan turns. one way sux air up the other forces it down. since hot air rises, u want the fan to circulate the hot air back down twards the floor during winter. and in the summer u want the air to get sucked back up to the top. understand now?
We have a big ceiling fan (4’ diameter)in our living room. I didn’t check which way ours is, but the blades are tilted so when the fan turns one way, blows down and vice versa… like a boat prop; I don’t know if the tilt is the same on all fans or if it depends on the make. Our living room is about 12X17 feet, with the standard 8 foot ceiling. End result of a small hot room and a big ceiling fan: there’s no such thing as drawing up cool air because the air volume is so low that the temp is the same throughout already. When it’s 30C inside, there IS NO cool air to draw up. Also, within a few seconds after turning on our fan, the air in a room is completely mixed so you don’t feel the effect of cool air coming up anymore. Remember… if you blow the warm air down, where’s it go when it hits the floor? - it fluffs back up and you end up with an even temp throughout. It depends on the design and layout of your house, but we only turn our fan on in the summer to create wind, and have it blowing down to evaporate the sweat from us. We tried it sucking up, but basically sat there sweltering in a well-mixed but still HOT room because there was no air blowing ON US. Basically all a ceiling fan does is mix the air in a room; not pump air from one place to another. The overall temperature will end up the same throughout the room whether it’s blowing down or up. The only thing you get to choose is whether you want the air blowing down directly on you (and scattering papers off the tables )or not.
MMMiiikeeee…You got it right. This is a question that has pondered in the minds of ceiling fans over.
Personally, it is all crap. Explainable well in theory, but it doesn’t work. The air blowing on you will make you cooler. It will circulate the air below more, which in itself will make you feel cooler. OTOH, if it is hot air. Turn the fan where it is blowing up. The cold air below will be forced up and warmed.
Personally, I keep it blowing down all year. It works best that way outside of theory.
I will not pretend to know how every fan in the world works, but here’s what I can tell you:
The clockwise/counterclockwise is pointless unless you can see which way the blades are tilted. Ever ceiling fan I have ever seen controls its direction by means of a switch on the side of the motor housing which has 2 positions. In the “up” position, the fan pulls air up through its blades; in the “down” position, the fan pushes air down through its blades.
Use the down position when it’s warm. This creates a breeze in the greatest part of the room and helps more too cool your skin, like any fan will.
Use the up position when it’s cool. This causes moves the air in the room up in the center and down along the walls, helping to keep the air circulating without creating so much of a detectable breeze. The effect is to keep so much of your heated air from accumulating near your ceiling but without the wind-chill effect of a fan blowing on you. You should also keep it to a lower speed setting in this mode.
Next week on the Straight Dope: Should the toilet paper hang over the top or down the back?
Our ceiling fans blow down in the summer – there’s nothing like the delicious chill of lying naked on the futon under them after getting out of a cool shower. Brrrrrrrr.
In the winter we just leave them off. Who wants a breeze when it’s ten below?
KneadtoKnow has it right. The value of a ceiling fan in the summer is to create a breeze in the main part of the room. The air is no cooler, but because of evaporative cooling (of your sweat), it feels cooler. To create this breeze, it must push the air down.
Why does pushing the air down create a better breeze than “sucking” the air up to the ceiling? Aerodynamics, my friends. Trust me on this, I’m an aerospace engineer. The moving blades of a fan induce momentum in the air molecules that pass through them (actually, in the air molecules that they pass through, but it depends on your perspective), causing the air to move directly away from the fan along its axis in a sort of cone. The air entering at the back of the fan is not so much “sucked” in by the fan as pushed in by the surrounding air as the fan creates a low pressure area at its back. As such, the air on the back moves more slowly.
Try an experiment: turn on a portable fan and place your hand on either side of it. One side will have a much stronger breeze than the other.
In winter, the object is to mix the warm air near the ceiling with the relatively cooler air near the floor. (In some rooms this may be fifteen degrees or more!) It may be equally efficient to do this whichever direction the fan is turning (I don’t know), but since you don’t need that cooling breeze, it’s just more comfortable to have it blow up toward the ceiling.
PS: The end of the toilet paper should obviously hang over the top of the roll. That makes it much easier for the cat to unroll it all over the floor. Trust me on this, I’m an engineer.
)or not.