How Much Attic Venting Do I Need

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.

How much attic venting do i need.

Calculate the total vent area needed. Take the total cubic feet per minute of air flow cfm of the fan and divide by 750 2. A 50 x 30 attic would have a total area of 1 500 sq. As a certified licensed home inspector it is not correct to say too much ventilation is bad for an attic unless rain moisture is getting in.

We always recommend at least having 1 sqft of net free area venting for every 750 cfm in your system. Do not use mechanical means electric attic fans. If the slope of your roof is greater than 6 12 you will need more ventilation to reflect the extra volume of attic space. Divide the attic s square footage by 150.

Federal housing authority recommends a minimum of at least 1 square foot of attic ventilation evenly split between intake and exhaust for every 300 square feet of attic floor space. You mention exhaust vents shouldn t exceed intake vents in the roof for proper circulation. Calculate 20 per cent more for 7 12 to 10 12 pitches and 30 per cent more for a pitch that is 11 12 or greater. The answer is rafter venting.

I need additional exhaust ventilation in my roof with the planned installation of a whole house fan in the attic of my home located in sf bay area. Ft divided by 150 equals 10 sq. Length x width of attic in feet 150 total sq. Ft of attic space for example 20 x 50 to be effective.

The federal housing administration recommends 1 square foot of attic ventilation for every 150 square feet of attic space. However with only two 1 ft x 2 ft gable roof vents i ll need an additional 7 sq ft of exhaust vents. Proper attic ventilation consists of a balance between air intake at your eaves soffits or fascias and air exhaust at or near your roof ridge. Of total vent space needed.

Ideally there should also be plenty of soffit intake space their calculations recommend 336 net square inches of open soffit. Venting plays a huge part in how your quietcool whole house fan system works to its full potential. This will give you the amount of net free venting in square feet required for the fan you select. Rafter vents or insulation baffles install in any rafter space to create narrow gaps that direct fresh air from the soffit vents to the peak of the roof.

Multiply the length of the attic times the width in feet to find the attic area then divide by 150 to find the total square feet of vent space needed. Here is an example.