Selecting a Whole House Fan*
Choosing the whole house fan that's right for you will depend upon your needs and the features you prefer. Whole house fans are characterized most often according to the volume of air they replace in cubic feet per minute (CFM) and by their drive mechanisms- direct drive or belt drive.
A fan properly sized for your home can make a complete air exchange in about 2-3 minutes. Five to ten air exchanges will cool not just the air, but the walls and furnishings as well. Those things contribute to heat buildup by absorbing heat throughout the day and releasing it at night. Running a whole house fan for about 20 minutes will cool these things sufficiently to make your home comfortable.
Most standard whole house fans move between 2,500 and 6,800 CFM of air, depending upon such factors as fan blade size, opening size, and available net free venting.
To determine the volume of your home in cubic feet, take the floor area in square feet and multiply that by the height of the ceilings. For example:
an 1,800 square foot home with an 8 foot ceiling height has a volume of 14,400 cubic feet. If you wish to replace that volume of air in, say, three minutes, you would require a whole house fan rated at 4,800 CFM. A higher CFM rated fan will replace the air in less than three minutes, while a lower CFM rated fan will replace the air in more than three minutes.