Expert: Howard Livingston - 7/9/2009

Question
Dear expert,
I am planning installing an attic fan in my 2-story house. My attic size is approximately 1200 sq.ft; there is no gable shutters, so I decided on a roof mounted fan. Seems like even the smallest Home Depot 1000 CFM fan should be adequate for up to 1600 sq.ft attic.
Two questions:
-for air intake I have (27) 12” wide X 12” long perforated soffits panels in my overhangs. That gives me 27 sq. ft of soffits. Per Amerimax manufacturer’s spec, they have 6 sq. in per 1 sq.ft air flow, to a total of 162 sq. in, or 1.125 sq. ft soffit air flow. I found a formula for required air flow: CFM:300 sq.ft, or in case of 1000 CFM fan: 1000:300=3.33 sq.ft  Seems that my soffits do not provide nearly enough air intake. Are my calculations right? What could be done to add missing 2 sq.ft of intake?
-I searched for attic fans online. The Broan brand 1000 CFM fan sells for $130-170. Similar Home Depot and Lowes models (AirVent or Master Flow) sell for $65-70. Are they different? Lower quality? Or just a brand recognition? There is also a Jet Fan similar model that sells for $309! What should I be looking for?
Thank you for the help.


Answer
The soffits vents will work === but if you remove one you will probably see a much smaller hole has ben cut in the soffit. Enlarge that hole to the max on every one. Vacuum the dust off the screen while you're at it. Then head for Home Depot. The fan will make a great difference of temps in the attic. Good for you !
Mount the fan as high as possible in the attic.