Ventilation Requirements - Field Controls VentCool Summit S-Class Series Installation Manual

VENTILATION REQUIREMENTS

It is very important that the attic be su ciently ventilated for the fan system to operate properly. Without
adequate ventilation, hot air exhausted from the home cannot easily escape from the attic, which creates back-
pressure that will substantially reduce the fan's performance. Operating this fan in an attic with less net free
ventilation area than recommended will decrease its air ow and energy e ciency.
For whole-house ventilation, we recommend a minimum of 1 square foot of "net free" ventilation area per 500 cfm
at a fan's highest speed for proper operation. Refer to speci cation table for required minimum Open Window
Ventilation Area in square feet when operating whole house fan.
Net free ventilation area can be provided by any combination of gable, eyebrow, roof cap, so t, or ridge
vents, or any other method of ventilating the attic space. The openings of most vents are partially obstructed by
grilles, louvers, and/or screens. A vent's "net free" ventilation area is the surface area of its opening minus the surface
area of any grilles, louvers, or screening covering it. Di erent types of vents have di erent ratios of net free area to
total area.
While most properly constructed homes have adequately ventilated attics, not all do. Because su cient ventilation
is a very strong factor in this fan's performance, it is important that the home's existing ventilation be veri ed before
it is installed.
Manufacturers typically publish their vents' net free ventilation areas and/or ratios in their products'
speci cation documents. If this information is unavailable, a ratio of 50% net free area to total area is usually a good
rule of thumb. A notable exception to this rule of thumb are ridge vents. The industry standard net free ventilation
area for ridge vents is 13% of the vent's length in feet.
Since most attics have multiple vents, often of di erent types, it is necessary to count each vent, noting its type
and size. Apply the appropriate ratio to the dimensions of each vent to nd its net free area, and sum these
values to nd the attic's total ventilation. An example of how these calculations are made is given in the
table below:
Vent Type Dimensions
Louver 24" x 24"
Ridge 10 feet
Round So t 10" diameter 3.14 x 5" x 5" / 144 = .55 ft.
Please consult a roo ng professional if the attic's net free ventilation area remains uncertain. Additional
ventilation may be required for proper operation of the fan system.
Refer to speci cation table for required minimum Open Window Ventilation Area in square feet when operating
whole house fan. Without adequate Open Window Ventilation Area, the quantity of cooler air pulled into the home
to be exhausted to attic may substantially reduce the fan's overall performance.
Total Area
2
24" x 24" / 144 = 4 ft.
n/a
2
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Net Free Area Ratio
("NFA")
50%
13%
50%
Total Net Free Ventilation Area:
Net Free Ventilation Area
(=Total Area x NFA)
2 2
4 ft. x .50 = 2 ft.
10 feet x .13 = 1.33 ft. 2
2 2
.55 ft. x .50 = 0.28 ft.
3.61 ft. 2
P/N 780104700 03/20 Rev A