For maximum effectiveness, a whole-house fan must be sized correctly for the structure it is required to ventilate.
The formula to follow for determining capacity is: square feet of living area x 3 = CFM (cubic feet of air moved per minute) required.
Because whole-house fans exhaust hot air into an attic, a properly sized attic ventilation system is required to exhaust heated air from the attic to outdoors.
To determine the net free area of attic ventilation required, use the following formula:
CFM rating of fan divided by 750 = square feet of net free exhaust area.
Failure to provide this venting will reduce the fan's airflow capacity. In addition, it will lead to noisy operation and ultimately failure of the fan motor.
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