Quote Originally Posted by Pepper
This is not complicated. Just buy a ceiling fan control. They cost sightly more because it's not the same as a dimmer.

1.5 Amp White Slide-To-Off Quiet Fan Speed Control

Pick a fan controller with a higher rating if yours needs more than 1.5 amps.
Listen to Pepper here. A/C motors, unless they come with variable speed build in, are not designed to run at varied speeds. A rheostat will increase resistance in the circuit which allows less power for the fan, causing the fan to spin slower than it should. This works for D/C circuits, but A/C is frequency modulated, not voltage. This can cause a lot of stress to the fan and can cause the motor to stall and overheat, with the possibility of catching fire.

Another difference between a rheostat and a fan speed controller is that a rheostat will operate from 0-100% whereas the fan controller will run something like 40-100%, which keeps the fan from stalling and becoming a hazard.

Fork out the extra $10 for all the good a real fan controller will do, it's worth it