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.
Fan death
Air movement will increase sweat evaporation, which cools the body. But in extreme heat – when the blown air is warmer than the body's temperature – it will increase the heat stress placed on the body, potentially speeding the onset of heat exhaustion and other detrimental conditions. The American Environmental Protection Agency (EPA) discourages people from using fans in closed rooms without ventilation when the heat index is above . The EPA does, however, approve of using a fan if a window is open and it is cooler outside, or when the heat index in a closed room is lower.