An undersized fan will fail to make the room comfortable and have to be run more often, using more energy in the process. An oversized fan will also use more energy and cut into the efficiency an Energy Star rating brings to the table.
When selecting a fan, start with the size of the room. A blade sweep — in most all cases the total width of a fan fixture — of up to 42″ is sized for a 12′ x 12′ room or 144 sq. ft. A blade sweep of 44″ is good for a room up to 225 sq. ft. Any room larger than 225 sq. ft. will require a blade sweep of 50″ or more.
There must be 7 feet of clearance between the ground and mounted fan blades. Anything lower poses the possibility of injury. 8 to 9 feet of clearance is ideal.
Most ceiling fans include a 3- to 5-inch downrod. This is the piece between the ceiling bracket and the fan housing. It creates enough space between the fan blades and the ceiling for optimal circulation. A fan can be mounted closer to the ceiling with low-profile “hugger” mounts. These mounts ensure the 7 feet of fan blade clearance, but they are less efficient.
How much air can a ceiling fan move? It depends on the fan’s CFM rating, or cubic feet per minute. The higher the CFM, the more air is moved. Some manufacturer’s don’t list the CFM, in which case you should look at the RPM (revolutions per minute) and the blade pitch (the angle of the blades). The more RPM and steeper the blade pitch, the more air is moved and usually with a larger motor.