What determines how fast ceiling fan spins?
#1
07-28-21, 06:33 PM
What determines how fast ceiling fan spins?
So over the years I've installed a total of 5 different ceiling fans throught our home. What I don't understand is how some of them spin really fast and blow alot of air. While others don't. Is it wattage, amps, CFM rating? Or just something I did wrong. I have all of them installed on speed switches with 3 different power levels. Just something that's perplexed me for over 10 years now.
#2
07-28-21, 06:45 PM
Group Moderator
It's all in the design. Blade size and pitch. Motor hp and speed.
One would think that the larger blades would create more air and normally they wood except if they're too close to the ceiling where they work opposite. The fan needs the ability to draw air over the blades to discharge down. I've seen the best air movement from smaller fans.
I have a 52" Hunter five blade custom ceiling hugger in my bedroom.
You wouldn't believe the noise it makes when the blades starve for air.
Overall..... I'd consider the air movement poor.
One would think that the larger blades would create more air and normally they wood except if they're too close to the ceiling where they work opposite. The fan needs the ability to draw air over the blades to discharge down. I've seen the best air movement from smaller fans.
I have a 52" Hunter five blade custom ceiling hugger in my bedroom.
You wouldn't believe the noise it makes when the blades starve for air.
Overall..... I'd consider the air movement poor.
#3
07-28-21, 07:05 PM
We're in an old farmhouse with window A/C, so 3 bedroom ceiling fans, den, kitchen and sunroom.
Agreed on motor HP, how many blades, how close to the ceiling.
I'd ALSO add that the pitch can make a big difference as well- both for balance, and air movement.
So, what I've done a few times is put an additional twist on the blades so they "bite" more air, which slows down the rotation a bit.
However, I've also had some which worked MUCH better taking 'shallower" bites of the air, and tossing it down at higher velocity.
Agreed on motor HP, how many blades, how close to the ceiling.
I'd ALSO add that the pitch can make a big difference as well- both for balance, and air movement.
So, what I've done a few times is put an additional twist on the blades so they "bite" more air, which slows down the rotation a bit.
However, I've also had some which worked MUCH better taking 'shallower" bites of the air, and tossing it down at higher velocity.
#4
07-29-21, 04:35 AM
Member
With reference to what PJ posted. For awhile they stopped making ceiling hugger fans just because of that problem. But people were not buying the fans because their rooms could not handle the drop tube. So the lesser of the two evils is poorer performance but the ability to have a fan in typical 7 to 8 foot bedroom ceiling.
#5
07-29-21, 08:22 AM
interesting stuff. didnt think about the closeness to the ceiling. Not all of mine are just not spinning very fast. the one in my sons room really cooks. whereas the others, different brands and models, spin not as fast.
#6
07-29-21, 09:47 AM
If you have several fans, (especially by the same manufacturer), you sometimes get lucky and can swap the blades between fans- the ceiling-hugger style seems to work better with longer blades, while the drop-fans can work with shorter blades.
#7
07-29-21, 01:00 PM
Group Moderator
The manufacturers put out recommendation charts but we all know bigger is better. 
When I replace mine I'll use a much smaller diameter fan.
When I replace mine I'll use a much smaller diameter fan.
#8
07-29-21, 01:52 PM
Member
But the smaller size fans also make more noise, especially at the high speed.
I have a 52" in our bedroom. Wife does not like the fan, but I do. At low speed it drives just enough air that I can feel it but she is willing to put up with it. Also very quiet at the low speed.
I have a 52" in our bedroom. Wife does not like the fan, but I do. At low speed it drives just enough air that I can feel it but she is willing to put up with it. Also very quiet at the low speed.
