Ceiling fans can reduce your energy bills up to 40% in the summer and 10% in the winter. Ceiling fan size (measured by the diameter of the fan in inches) is determined by the square footage of the room: 29"(up to 75 square feet), 42"(76-144 square feet), 52"(145-250 square feet), 60"(vaulted ceilings and rooms 250-500 square feet). Longer rooms and vaulted ceilings often require more than one ceiling fan. The greater the blade pitch, the more air it will move (14