Installing a whole house fan is an energy efficient alternative that can complement your central air conditioning. A whole house fan is a large louvered fan, installed in the ceiling of the top floor of your house. These fans work on the principle that there is cooler air outside the house in the early mornings and evenings. By switching on the fan and keeping the windows open, cool air is sucked into the house dispersing the warm air out through the attic. Whole house fans are usually run whenever the outdoor temperatures are lower than indoor temperatures. Controls for a whole house fan may be a simple on / off pull or wall switch. Fans may have automatic timers that allow them to be automatically turned on or off at a preset time.