When you re finished write the number down somewhere you ll need it to find the right size piece of plywood for your attic fan to be installed on.
How to size an attic exhaust fan.
Next multiply the square feet of attic space by 0 7 to get the minimum number of cubic feet of air per.
Cfm cubic feet per minute is a measure of the amount of air the fan moves in a minute.
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.
If you need 6 000 cfm of air flow through your house divide 6 000 by 750 to get a minimum 8 square feet of attic venting.
You now need to multiply 960 x 15.
The minimum requirements say that this air should be changed 15 times an hour.
That translates to one attic vent 3 feet by 3 feet or two attic vents.
To determine the size of your attic multiply the width by the length of the attic floor in feet.
You multiply length times width times height.
The formula above gives an approximate value of the cfm needed for an attic fan.
Measure the distance between the studs on the left and right side of your vent.
This attic ventilation calculator computes the size and number of solar powered attic fans to achieve the proper ventilation for your attic.
10 feet x 12 feet x 8 feet that computes to 960 cubic feet of air in the room.