Step 1. Calculate the required CFM (air flow).

Method A:  I know the dimensions of my attic space. (more accurate)

Attic Configuration

Attic Area: 500 sq. ft. 600 sq. ft. 700 sq. ft. 800 sq. ft. 900 sq. ft. 1,000 sq. ft. 1,100 sq. ft. 1,200 sq. ft. 1,300 sq. ft. 1,400 sq. ft. 1,500 sq. ft. 1,600 sq. ft. 1,700 sq. ft. 1,800 sq. ft. 1,900 sq. ft. 2,000 sq. ft. 2,100 sq. ft. 2,200 sq. ft. 2,300 sq. ft. 2,400 sq. ft. 2,500 sq. ft. 2,600 sq. ft. 2,700 sq. ft. 2,800 sq. ft. 2,900 sq. ft. 3,000 sq. ft. 3,100 sq. ft. 3,200 sq. ft. 3,300 sq. ft. 3,400 sq. ft. 3,500 sq. ft. 3,600 sq. ft. 3,700 sq. ft. 3,800 sq. ft. 3,900 sq. ft. 4,000 sq. ft. 4,100 sq. ft. 4,200 sq. ft. 4,300 sq. ft. 4,400 sq. ft. 4,500 sq. ft. 4,600 sq. ft. 4,700 sq. ft. 4,800 sq. ft. 4,900 sq. ft. 5,000 sq. ft. 5,100 sq. ft. 5,200 sq. ft. 5,300 sq. ft. 5,400 sq. ft. 5,500 sq. ft. 5,600 sq. ft. 5,700 sq. ft. 5,800 sq. ft. 5,900 sq. ft. 6,000 sq. ft. 6,100 sq. ft. 6,200 sq. ft. 6,300 sq. ft. 6,400 sq. ft. 6,500 sq. ft. 6,600 sq. ft. 6,700 sq. ft. 6,800 sq. ft. 6,900 sq. ft. 7,000 sq. ft. 7,100 sq. ft. 7,200 sq. ft. 7,300 sq. ft. 7,400 sq. ft. 7,500 sq. ft. 7,600 sq. ft. 7,700 sq. ft. 7,800 sq. ft. 7,900 sq. ft. 8,000 sq. ft. 8,100 sq. ft. 8,200 sq. ft. 8,300 sq. ft. 8,400 sq. ft. 8,500 sq. ft. 8,600 sq. ft. 8,700 sq. ft. 8,800 sq. ft. 8,900 sq. ft. 9,000 sq. ft. 9,100 sq. ft. 9,200 sq. ft. 9,300 sq. ft. 9,400 sq. ft. 9,500 sq. ft. 9,600 sq. ft. 9,700 sq. ft. 9,800 sq. ft. 9,900 sq. ft. 10,000 sq. ft.
Attic Height: 2 ft. 3 ft. 4 ft. 5 ft. 6 ft. 7 ft. 8 ft. 9 ft. 10 ft. 11 ft. 12 ft. 13 ft. 14 ft. 15 ft. 16 ft. 17 ft. 18 ft. 19 ft. 20 ft. 21 ft. 22 ft. 23 ft. 24 ft.
Roof Construction: Gable Hip
Roof Color: Dark (black, gray, brown) Light (white, tan, etc)

Required CFM:

Proceed to Step 2 and use the chart to determine the size and number of solar-powered attic ventilation fans required to achieve a min. ventilation rate of 10 air changes per hour.

Method B:  I don't know the dimensions of my attic space.

Home Configuration

Home Square Footage: 500 sq. ft. 600 sq. ft. 700 sq. ft. 800 sq. ft. 900 sq. ft. 1,000 sq. ft. 1,100 sq. ft. 1,200 sq. ft. 1,300 sq. ft. 1,400 sq. ft. 1,500 sq. ft. 1,600 sq. ft. 1,700 sq. ft. 1,800 sq. ft. 1,900 sq. ft. 2,000 sq. ft. 2,100 sq. ft. 2,200 sq. ft. 2,300 sq. ft. 2,400 sq. ft. 2,500 sq. ft. 2,600 sq. ft. 2,700 sq. ft. 2,800 sq. ft. 2,900 sq. ft. 3,000 sq. ft. 3,100 sq. ft. 3,200 sq. ft. 3,300 sq. ft. 3,400 sq. ft. 3,500 sq. ft. 3,600 sq. ft. 3,700 sq. ft. 3,800 sq. ft. 3,900 sq. ft. 4,000 sq. ft. 4,100 sq. ft. 4,200 sq. ft. 4,300 sq. ft. 4,400 sq. ft. 4,500 sq. ft. 4,600 sq. ft. 4,700 sq. ft. 4,800 sq. ft. 4,900 sq. ft. 5,000 sq. ft. 5,100 sq. ft. 5,200 sq. ft. 5,300 sq. ft. 5,400 sq. ft. 5,500 sq. ft. 5,600 sq. ft. 5,700 sq. ft. 5,800 sq. ft. 5,900 sq. ft. 6,000 sq. ft. 6,100 sq. ft. 6,200 sq. ft. 6,300 sq. ft. 6,400 sq. ft. 6,500 sq. ft. 6,600 sq. ft. 6,700 sq. ft. 6,800 sq. ft. 6,900 sq. ft. 7,000 sq. ft. 7,100 sq. ft. 7,200 sq. ft. 7,300 sq. ft. 7,400 sq. ft. 7,500 sq. ft. 7,600 sq. ft. 7,700 sq. ft. 7,800 sq. ft. 7,900 sq. ft. 8,000 sq. ft. 8,100 sq. ft. 8,200 sq. ft. 8,300 sq. ft. 8,400 sq. ft. 8,500 sq. ft. 8,600 sq. ft. 8,700 sq. ft. 8,800 sq. ft. 8,900 sq. ft. 9,000 sq. ft. 9,100 sq. ft. 9,200 sq. ft. 9,300 sq. ft. 9,400 sq. ft. 9,500 sq. ft. 9,600 sq. ft. 9,700 sq. ft. 9,800 sq. ft. 9,900 sq. ft. 10,000 sq. ft.
Garage: Attached, Single Car Attached, Double Car Attached, Triple Car Detached or None
Number of Stories: Single Story One and a half Two Story Three Story
Roof Color: Dark (black, gray, brown) Light (white, tan, etc)
Roof Pitch: Normal (7:12 or less) Steep (8:12 or more)

Required CFM:

Proceed to Step 2 and use the chart to determine the size and number of solar-powered attic ventilation fans required to achieve a min. ventilation rate of 10 air changes per hour.