Unfortunately, many ceiling fans have been installed on electrical boxes designed for light fixtures, not the fan-rated boxes required by code. This means the fan is attached to a box that isn't designed for the additional load. A fan installed this way could eventually come crashing down.
A properly mounted fan will be attached to a fan-rated box, mounted either on a 2x4 with lag screws or to an adjustable fan brace. To be certain how the fan is mounted, you may ultimately need to make a trip to the attic. But first loosen the bracket housing and take a look from below. A fan-rated box is usually so labeled, and you'll usually see hexagonal heads of lag bolts attaching it to a wood brace, or U-bolts attaching it to a metal brace.
Next, test the fan support bracket for sturdiness. If you can move the bracket easily, tighten it. If you can't tighten it, or if the box is the wrong type, install an adjustable fan brace (available at home centers).
- Make sure the tooth on the fan support bracket is resting in the slot on the ball joint.
- Test all bolts and screws for tightness, especially where the fan blades attach to the blade iron and where the blade irons mount to the motor spindle.
- Check the blades and blade irons with a story board. Hold the story board in a single spot, bring each blade end to it, and mark each spot. The variance should be less than 1/4 in. Typically, manufacturers will replace warped blades or bent blade irons.
If none of the fixes above solve the problem, try balancing the blades. Balancing kits are available at lighting stores, but you can also use coins. Start by taping a dime to the middle of a single blade and turning the fan on high. Repeat this test for each blade until you find the one where the wobble starts to lessen. Then move the coin up and down the blade, trying heavier coins as necessary, until you find the optimal balance.