There is a very significant difference between a whole-house fan and an attic fan and how their applications are used. An attic fan is used to remove hot air from the attic space in order to limit heat transfer to the living space below. In general, a cooling unit for the rest of the house is still needed. A whole house fan is mounted in the ceiling between the living space and the attic. It is used to suck warm air out of the living space up into the attic. The pressure created by the suction forces warm air out of the venting of the roof and it helps draw cooler outside air in through open windows in the house. Generally, a whole-house fan is most efficient during the evening hours and can in many cases be significantly more energy efficient than an air conditioner.