A whole house fan is located in the attic, designed to exhaust air from the living space into the attic during the evening. When the fan is turned on the air in the living space is exhausted into the attic, creating negative pressure inside the house, which draws cooler evening air into the house. At the same time the air exhausted into the attic is pushed out of the house through attic vents. The fan essentially accelerates the natural cooling that would occur during the evening by having windows open at night.
For a whole house fan to have the desired effect there needs to be adequate attic ventilation to allow the exhausted air to be pushed out of the house when the fan is running (1 sq. ft. net free area per 1,000 cfm of air being exhausted is recommended).