A ceiling fan should leave at least 7 feet from the floor to the bottom of the fan, so that you and your guests do not injure yourselves on the turning fan blades. If your ceilings are 8 feet, you should have a flush mounted fan to allow 7 feet underneath. Optimal ceiling fan height is 7-9 feet to create good air flow. For example, if your ceilings are 15 feet high, a 5 foot downrod is recommended, which leaves 9 feet from the bottom of the fan to the floor.