Hi, I have someone installed a ceiling fan by harbor breeze. The fan wobble a little when it is on. Is it normal? I have used an 18 inches extension rod. But also, they have installed the fan at the middle of a vaulted ceiling. They should install it on one side of the ceiling (the fan allow this mounting without) but they install it a the middle creating a small gap between fan and ceiling. Please advice.

It is normal, but if it bothers you, you can balance the blades. See:

Ceiling fan blade balancing issues - Ceiling Fans N More (http://www.ceiling-fans-n-more.com/blade-balancing-issues.php)