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.

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. In other words the entire vent opening doesn t count as vented space. The purpose of attic ventilation is obvious in the summer when hot air collects in the attic and makes the entire house uncomfortable. The gable vent you purchase should be sufficient for the size of your attic.

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. That said air resistance and interference such as vent grates reduces the area of true ventilation. Allows cool dry air to enter the attic. Calculate the square root of the total.

In order to facilitate this exchange of warm and cool air the general rule of thumb suggests installing at least 1 sq. Vent size for an attic. 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. Ventsure inflow intake vent.

Therefore your return air duct and grill size will be 24 by 24 inches. Choose one of the following products to meet the recommended intake nfva of 528 square inches. Vent pipes shall not be less than 1 1 4 inches 32 mm in diameter. This helps make it easy to calculate how many vents you need for your attic once you ve determined your requirements.

The square root of 576 is 24. At the same time getting a vent that is too large for the attic is a mistake. 4 ton unit x 144 square inches 576 squared. 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.

The following product options will allow you to achieve an intake nfva of 528 square inches. Next multiply the square feet of attic space by 0 7 to get the minimum number of cubic feet of air per. 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. 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.

It is a big mistake to assume that just any gable vent will work for your attic.