Ceiling fan
A ceiling fan is a mechanical fan mounted on the ceiling of a room or space, usually electrically powered, suspended from the ceiling of a room, that uses hub-mounted rotating blades to circulate air. Ceiling fans typically rotate more slowly than other types of circulating fans, such as electric desk fans. They cool people effectively by introducing slow movement into the otherwise still, hot air of a room. Fans never actually cool air, unlike air-conditioning equipment, they in fact heat the air due to the waste heat from the motor and friction, but use significantly less power (cooling air is thermodynamically expensive). Conversely, a ceiling fan can also be used to reduce the stratification of warm air in a room by forcing it down to affect both occupants' sensations and thermostat readings, thereby improving climate control energy efficiency.
Ceiling fan
Another concern with installing a ceiling fan relates to the height of the blades relative to the floor. Building codes throughout the United States prohibit residential ceiling fans from being mounted with the blades closer than seven feet from the floor; this sometimes proves, however, to not be high enough. If a ceiling fan is turned on and a person fully extends his or her arms into the air, as sometimes happens during normal tasks such as stretching or changing bedsheets, it is possible for the blades to strike their hands, potentially causing injury. Also, if one is carrying a long and awkward object, one end may inadvertently enter the path of rotation of a ceiling fan's blades, which can cause damage to the fan. Building codes throughout the United States also prohibit industrial ceiling fans from being mounted with the blades closer than 10 feet from the floor for these reasons.