By Gene and Katie Hamilton
Air circulation in the attic is important because on hot days it prevents the space from overheating. When the thermometer drops, proper air flow reduces attic humidity and improves insulation performance.
A contractor will charge $358 to install a 14-inch power ventilator which includes the labor and material; you can do it for more than half and pocket a 65 percent savings. That's assuming you have carpentry experience and don't have a steeply pitched roof. If the idea of working on the roof and cutting a hole in it is too intimidating, don't hesitate to hire out the job.
For about $125 you can buy what you need: a power ventilator, an electrical box and cover, a short piece of three-wire BX or Romex cable, a package of wire nuts and a quart of roofing cement. An electrical circuit is needed to power the fan. If there isn't one already in the attic, call an electrician.
You'll need basic carpentry tools, and for cutting the roof opening rent a reciprocating saw. While you're working on the roof, you'll need someone inside the attic to help you.
Tip: Check the manufacturer's recommendations for the amount of intake vents required for the fan to run efficiently. You might have to install additional vents in the eaves or gable ends.
Figure the job will take you the better part of a day from start to finish, while a contractor who does the job often will finish up in about four hours.
Gable or soffit louvered vents are required as fresh air intakes for powered attic ventilators.
The Home Ventilating Institute recommends that a powered attic ventilator should provide at least ten air changes per hour. To determine the proper CFM (cubic feet per minute) rating for a fan which will provide that number of air changes, multiply the total square footage of your attic by .7.
To find the total square footage multiply the length of the attic times its width. Let’s say it comes out as 1500 square feet.
1500x.7 = 1050 CFM
That means a fan with a 1050 CFM rating is needed.
Here's more ventilation information from the Home Ventilating Institute Consumer Publications for Homeowners.
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The average price to install a roof vent noted above is cost data to compare a contractor’s estimate with doing it yourself. Tweak the data by adding your ZIP Code to find a local cost.
Improvement and Repair Cost Updated 2019