A whole-house fan pulls in cool air from the outside, for times when the inside of a house is hotter than outside. Whole house fans cool efficiently, relying on drawing in outside cool air, instead of using up vast amounts of electricity to cool warm air.
Whole house fans cool multi-story homes much more cost-effectively than most air conditioning systems. If a climate is such that the temperature drops considerably in the evenings, leaving homes considerably hotter than the outside, using a whole house fan will take advantage of the outside cool air and force it into the house, while expelling it out of the rest of the house.
Houses with plenty of windows can take increased advantage of the airflow, using the openings to draw in more air than just relying on the breeze. The potential of a whole house fan is multiplied with each source of air flowing into the house.
Whole house fans also generate considerably less noise than other air conditioning or HVAC systems. The single fan creates noise from the movement of air and the motor running. If a whole house fan is mounted in the attic, the noise insulation will be increased as well.