Varying blades’ rotation and speed can better distribute cool and warm air, lower energy costs
One of the basic things we all understand about heat is that it rises. As air molecules warm up, they expand and become lighter, and that causes them to head up toward the ceiling of a room, which isn’t necessarily where you want them.
This natural rising can create layers within a room, with cooler air down near the floor, and warmer air trapped up near the ceiling. That’s especially true if you have ceiling-mounted heat registers, where your heat is entering the room at a higher level to start with. And of course, the higher the ceilings, the more that heat can rise, and the warmer the temperatures will get up near the peak.
The same is going to be the case with cooler air. When summer finally gets here and we switch back to air conditioning, cooler air is going to want to fall and settle near the floor of a room, to the detriment of those spaces on the upper levels. And here again, if you have air conditioning ducts in the floor, the effect is going to be that much more pronounced.
Stirring things up
Sizing things up
When considering a ceiling fan, the first order of business is deciding on the size. Fans are sized by the overall diameter of the blades, such as 36-inch, and will have anywhere from three to five blades. For the most part, the more blades and the larger the diameter, the more air movement you’ll have, although some large-diameter, industrial-style fans move quite a bit of air with only three blades.
As a general rule of thumb, a fan with a diameter of 36 to 44 inches will handle a room up to about 225 square feet, and a fan with a 52 or 54 inch diameter will handle about 400 square feet. For rooms that have more square feet than that, simply use more fans.
Ideally, the fans should be installed with the blades about 7 to 10 inches from the ceiling. Any closer than that and you won’t get a good air movement to stir up the stagnant air along the ceiling. Also, the blades should be at least 18 inches away from the wall.
Most ceiling fans have the option of multiple speeds, so this is also a consideration when choosing a size. Larger blades have the capability of moving more air at a slower speed, so if you have relatively low ceilings, that can be a real advantage when you don’t want the fan to be blowing loose papers around!
So which way is up?
If you look at the fan blades from the end, you’ll see that they’re angled in relation to the floor, rather than being exactly parallel. It’s that angle that allows them to move air as they turn, like a horizontal airplane propeller. Most fans have a reversing switch, which allows the motor to run either clockwise or counterclockwise. In one direction, the angle of the blades will pull air up from the floor toward the ceiling; in the other direction, the blades will push the air down from the ceiling toward the floor.
If you have a very high ceiling, such as a room with a two story vault, you’d like to get the warm air that’s trapped up there pushed down, so the lower floors can take advantage of it. Typically, that means that the fan rotation should be such that the blades are pushing the air down. However, in homes with lower ceilings, that downward push of air, even though it’s pushing the heat down, may also create an unpleasant breeze that actually makes you feel cold.
In that case, reverse the motor so the blades are pulling the air up. That will create a convection current of air against the ceiling, and push the warm air that’s up there outward and down the exterior walls, which again stirs things up.
The bottom line is that getting things where you want it from a heat distribution standpoint may take a bit of trial and error, with a combination of both blade rotation and blade speed.
For cooling, things are usually a bit more straightforward. Most people prefer to have the fan rotation set so the blades are pushing the air down, which stirs up the air and creates a nice cooling breeze. Set the speed at whatever level you’re comfortable with, and you should find that you can save money by cutting back on how often you run your air conditioning.
Source: “Ceiling fan provides relief in 2 ways” by Paul Bianchina, Inman News, February 22, 2013