Field Controls VentCool 2.4 Installation Manual Download Page 4

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VENTILATION REQUIREMENTS

It is

critical

that the attic be suffi ciently ventilated for this fan to operate properly. Without adequate ventilation,

hot air cannot easily escape from the attic, which creates back-pressure that can substantially reduce the fan’s
performance. Venting requirements vary by fan. We recommend

a minimum

of 1 sq. ft. of “net free”

ventilation area per 500 cfm at a fan’s highest speed.

Therefore, the VentCool 2.4, 3.4 and 4.9 Whole House Fans

require a minimum square feet of net free ventilation area for proper operation. Refer to Table 1 for net

require a minimum square feet of net free ventilation area for proper operation. Refer to Table 1 for net
free ventilation area per model.

free ventilation area per model.

TABLE 1: MInimum Net Free Ventilation Area Required

Operating this fan in an attic with less net free ventilation area than recommended will decrease its airfl ow and
energy effi ciency. Net free ventilation area can be provided by any combination of gable, eyebrow, roof cap,
soffi 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 then the surface area of its opening minus the surface area of any grilles, louvers, or screening covering it.
Different types of vents have different ratios of net free area to total area. Manufacturers typically publish these
ratios with their vents’ specifi cations, but if this information is not available to you, a ratio of 50% net free area
to total area is usually a good rule of thumb. For example, according to this rule of thumb, a typical 24” x 24”
louver with a gross area of 4 sq. ft. would have a net free area of 2 sq. ft. A notable exception to this rule are
ridge vents. The industry standard net free ventilation area for ridge vents is 13% of the vent’s length in feet.
While in our experience most properly constructed homes have adequately ventilated attics, not all do. Because
suffi cient ventilation is so critical to this fan’s performance, it is important that the home’s existing ventilation
be verifi ed before it is installed. Since most attics have multiple vents, often of different types, it is necessary
to count each vent, noting its type and s ize. Then, apply the appropriate ratio to each vent to fi nd its net free
area, and sum these values to fi nd the attic’s total ventilation. An example of how these calculations are made
is given in TABLE 2 below:

TABLE 2: Net Free Attic Ventilation Example of Calculations

Please consult a roofi ng professional if the attic’s net free ventilation area remains uncertain.

WHERE TO LOCATE THIS FAN

The best location for this fan is dictated by its theory of operation: As a
home heats up during the day, a large amount of heat is retained in its
structure and contents. These materials give up their heat slowly and, in
doing so, continue to heat the home’s interior even though the outdoor
temperature may, in fact, be very comfortable in the evening and at night.
Thus, homeowners are forced to either endure the hot conditions inside of
their homes or turn on their air conditioners and bear the expense thereof.
When operated properly, this whole house fan can resolve this
dilemma by forcing the hot air inside a home out and drawing cool air
from outside in. The illustration, to the right, depicts how this fan
exhausts hot air into the attic and draws cool air into the house from out-
doors through open windows and/or doors.

Model

Minimum Net Free Ventilation Area (sq ft)

VentCool 2.4

6.3

VentCool 3.4

6.7

VentCool 4.9

10.4

Vent Type

Dimensions

Total Area

Net Free Area