Before you buy a fan, consider the size of the room you want to cool. A 52-inch fan is appropriate for a room that's 230 square feet or larger, while a 42-inch fan is appropriate for rooms ranging in size from 150 to 229 square feet.
For a ceiling fan to move the right amount of air, its blades should be set at a 14 degree angle. Blades set at a 10 degree angle will simply slice the air, while blades at a 20-degree angle will meet so much resistance that the motor may burn out.
Set fan clearance at 9 feet above the floor if possible (if this is not possible, maintain a minimum clearance of 7 feet. This will help you and your family avoid injuries. Conversly, don't fit the ceiling fan too snugly to the ceiling; doing so will prevent it from circulating air properly.