How Many Attic Fans Are Needed

An attic fan is installed on the slanted side of your roof or on one of the gable sides of your attic.

How many attic fans are needed.

Ideally there should also be plenty of soffit intake space their calculations recommend 336 net square inches of open soffit ventilation to supply 700 cfm. Note that these two feet would not need to be one large opening. Attic fans exhaust hot air from your attic to the outside. It doesn t matter if the ventilation openings are spread out as long as there is sufficient space for all the air to escape.

How an attic fan works. Ok i would definitely not recommend an attic fan. Ft of attic space for example 20 x 50 to be effective. Federal housing authority recommends a minimum of at least 1 square foot of attic ventilation for every 300 square feet of attic floor space evenly split between intake and exhaust.

Because what happens is attic fans are so strong that they actually reach down into the conditioned space of your house and they do that by using the wall cavities and where the outlets and pipes come through the walls as places where they draw air from the inside of your house it s that air conditioned air and it ll pull it right up into the attic and exhaust it outside. If your roof is 1200 sq ft soffit floor space you will need 4 sq feet of roof ventilation. According to their requirements you should have 1 square foot of attic ventilation per 300 sq ft of attic floor space. So if your fan is rated at 1500 cfm you will need about two feet of totally open space in your attic.

Use only soffit vents as fresh air intakes for powered attic ventilators. The uniform building code requires that the amount of venting area in the attic be equal to 1 150 of the area of the floor and in most circumstances it allows a ratio of 1. With square foot living space at a premium many homeowners turn to their attics for a little extra room. A minimum of one square foot of inlet area for every 300 cfm of hvi certified fan capacity is required for proper fan operation.

There should also be a 50 50 balance of attic venting and roof venting. According to the home ventilating institute hvi powered attic ventilators need to move a minimum of 700 cubic feet per minute cfm for 1 000 sq. Vent fan location locate roof mounted fans on the back of the roof below the ridge but not so high as to be visible from the front of the house in the middle of the main part of the attic. Attic vent fans are commonly rated from 800 to 1 600 cfm making one fans suitable for attics of up to around 2 200 square feet.