I hope that your ceiling is properly blocked for the chandelier. Please make sure that it is! There is no set rule that I know of about chandelier height in a family room with a 30' cathedral ceiling. You want the light to be low enough to light the room, but not so low that it blocks a view. I'd say that the bottom of the chandelier should be between 12 and 15', and I'd likely take a look at it at 12' and then decide. I suggest you do a scaled drawing of the room with the chandelier in it.
Carolyn Albert-Kincl, ASID

Thank you for your expertise!!!