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How to Size and Use a Whole House Fan

Using a whole-house fan properly can lower cooling costs, reduce indoor allergens, and freshen the atmosphere of your home. Whole-house fans work by moving hot air out through gables or other attic vents and drawing cooler air in through open windows or doors. As a result, Whole-house fans do not work very well when the outdoor temperature is not less than 10 degrees cooler than the indoor temperature or when the outdoor humidity is high.

In order to determine the size of the fan your home will need, calculate the square footage of your home. Most whole-house fan manufacturers will list the capability of the fan to the square footage of your house. A common believe is that a complete change of the air in the home should be accomplished every 3 or 4 minutes.

Most fans include a CFM (Cubic Feet of air per Minute) rating. The greater the CFM value, the more air it can move. Simply divide your home’s cubic feet by the fan’s CFM rating to determine the number of minutes it will take to exchange the air. A 2000 square foot home with 8-foot high ceilings will have all the air in the house completely changed in 8 minutes with a 2000 CFM fan.

Here’s how you arrive at those figures. A 2000 CFM fan moves 2000 cubic foot volume of air in a minute. A 2000 square foot house with an 8 foot high ceilings has 16,000 cubic feet of space (2,000 sq/ft area * 8 ft = 16,000 cubic feet). 16,000 cubic feet of space divided by the capacity of the fan, 2,000 cubic feet per minute, equals 8 minutes (16,000 cu/ft volume of air divided by 2,000 cu/ft of air moved per minute = 8 minutes to move that volume of air).

NOTE: When you use the whole house fan, you also clear out your attic of harmful moisture and heat build up, which will increase the functional life of your roof. A whole house fan costs pennies an hour to operate. It’s a cost-effective alternative to air conditioning. Click on the following for more info on properly sizing a whole house fans


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