Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
In South Korea, it is commonly believed that sleeping in a closed room with an electric fan running can be fatal. According to the Korean government, "In some cases, a fan turned on too long can cause death from suffocation, hypothermia, or fire from overheating." The Korea Consumer Protection Board issued a consumer safety alert recommending that electric fans be set on timers, direction changed and doors left open. Belief in fan death is common even among knowledgeable medical professionals in Korea. According to Yeon Dong-su, dean of Kwandong University's medical school, "If it is completely sealed, then in the current of an electric fan, the temperature can drop low enough to cause a person to die of hypothermia." Although an air conditioner transfers heat from the air and cools it, a fan moves air to increase the evaporation of sweat. Due to energy losses, a fan will slowly heat a room.