How Big Should Attic Vents Be

To determine the size of your attic multiply the width by the length of the attic floor in feet.

How big should attic vents be.

If your attic floor has a vapor barrier you will need one square foot of nfa per every 300 square feet of attic floor area half of that will be intake half for exhaust. Ventsure inflow intake vent. At the same time getting a vent that is too large for the attic is a mistake. The area of the vent is specified on the packaging as the net free area the gable vent should provide 1 square inch of outlet and inlet area for every square foot of the attic.

Choose one of the following products to meet the recommended intake nfva of 528 square inches. Vents exceeding 40 feet 12 192 mm in developed length shall be increased by one nominal pipe size for the entire developed length of the vent pipe. Ideally half the vents should be located in the soffit at the bottom of the roof and half in gable or ridge vents near the top to allow for natural circulation of air through the attic. But venting has an equally important.

The gable vent you purchase should be sufficient for the size of your attic. Vent size for an attic. It is a big mistake to assume that just any gable vent will work for your attic. 4 ton unit x 144 square inches 576 squared.

Next multiply the square feet of attic space by 0 7 to get the minimum number of cubic feet of air per. Allows cool dry air to enter the attic. Vent pipes shall not be less than 1 1 4 inches 32 mm in diameter. How to size attic exhaust vent fans for your home attic size.

Calculate the square root of the total. Therefore your return air duct and grill size will be 24 by 24 inches. The following product options will allow you to achieve an intake nfva of 528 square inches. The square root of 576 is 24.

The purpose of attic ventilation is obvious in the summer when hot air collects in the attic and makes the entire house uncomfortable. Generally speaking you need a ratio of 1 300 where for every 300 square feet of ceiling space you need 1 square foot of attic ventilation. In other words the entire vent opening doesn t count as vented space. That said air resistance and interference such as vent grates reduces the area of true ventilation.

The general rule of thumb on the amount of total attic vent space needed is to have at least one square foot of vent space for every 150 square feet of attic area.