Friday, September 28, 2007

Sizing Your Attic Fan

Determining the amount of airflow in cubic feet per minute (cfm) that the whole house fan should provide involves a simple calculation. Multiply the total gross square footage of the house (include upstairs area)by the ceiling height (typically 8 feet). Select a fan that delivers between one-half to one times that amount of cfm at 0.1" static pressure. For example, a 25' x 40' one-story home is 1,000 square feet and would need an 8 x 1,000 x 1/2 = 4,000 cfm fan or better. A two-speed unit that delivers 4,500 cfm at the high setting (240 watts) and 3,200 cfm at low (120 watts) should be adequate.

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