This answer is based on the 2017 NEC. A. Outlet boxes for a ceiling paddle fan must be listed and marked as suitable for the purpose, and must not support a fan weighing more than 70 lbs. Outlet boxes ...
The fear of being zapped into next week—or beyond—keeps even some intrepid do-it-yourselfers away from electrical work. Generally speaking, that's wise, because messing with electricity can be lethal.