Frequently Asked Questions

How much attic ventilation is required for my home?
Last Updated 5 years ago

Lomanco recommends 1 square foot of attic ventilation for every 300 square feet of attic floor space (50% exhaust and 50% in intake)  Let’s go through an example… For a home with 1,500 square feet of attic floor space, you’ll divide 1,500 by 300 = 5 square feet of attic ventilation.  You divide 5 by 2 to provide half of the ventilation for intake and half as exhaust.  Thus, 5 divided by 2 = 2.5 square feet of attic ventilation for intake and 2.5 square feet of attic ventilation for exhaust.  To determine how many vents you will need, take the square feet recommended and multiply by 144 to convert to square inches.  Thus, 2.5 X 144 = 360 square inches of attic ventilation is required for exhaust and 360 square inches for intake.  Once you have determined how many square inches of ventilation you need and the Net Free Area of the product you are using, divide the Net Free Area (NFA) rating of the product by the NFA required.  For example, the Lomanco 750 provides 50 square inches of ventilation, so if you are using the 750, you’ll divide 360 by 50. Thus, you would need 7.2 vents (8 because you always want to round up).

(NOTE: Some local building codes require that 1 square foot of ventilation be provided for every 150 square feet of attic space.  Please check with your local building code office to ensure compliance to local requirements.)

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