How Much Cfm Do I Need For Attic Fan

To calculate the amount of attic exhaust area you will need divide the fan s capacity in cfm by 750.

How much cfm do i need for attic fan.

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. You need a minimum of 1 square foot of attic air venting for each 750 cfm of air flow. The formula above gives an approximate value of the cfm needed for an attic fan. 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.

17600 cubic feet 1600 11. 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. What this means is that every eleven minutes the air in the home is being exchanged by a fan of this rating along with having windows open in each room. Ventilation rate of 10 air changes per hour.

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. Ft of attic space for example 20 x 50 to be effective. Use the chart below as an attic vent fan cfm calculator. For proper cooling and efficient operation any whole house comfort ventilator requires adequate unobstructed outlets in the attic through soffit vents grilles or louvers.

Divide the cubic feet measurement by the cfm rating assigned to the fan. Attic fan size cfm 0 7 x sq ft area of the attic formula 1 the size of an attic fan is calculated in terms of cfm.