Whole House Fan

Whole house fans are used when the outside air is cool, as in the morning. They draw air through your open windows and force it up through the ceiling, into the attic where it is exhausted out the vents. In the process, the entire house is cooled by fresh air. Whole house fans use much less energy and are much cheaper to run than air conditioning.

Whole house fans typically have louvered-shutters over a vent at a central location, such as your hall ceiling. The louvers prevent cooled or heated air from escaping when the fan is not in use.

--  from California Life, The Sacramento Bee, August 10, 1996.