Guidelines for locating your whole house fan:
•
Centrally located to ensure air is drawn evenly from multiple open windows
•
AWAY from windows that will be opened so cool air is required to travel a long path to the fan
•
At the highest point possible to exploit natural convective action
•
Near an outlet or power supply to minimize electrical work
•
Typically, the ideal location in a two-story home is in the open area at the top of the stairs
•
Try avoid narrow spaces close to bedrooms, as this could amplify noise at night
(when noise perception is strongest)
Ceiling or Wall?
The 2.5/2.5e WHF intake box can be mounted in either the horizontal or vertical orientation. Our
recommended location is on a ceiling in the horizontal orientation -- keep in mind that it makes sense
to place the unit as high as possible to eliminate the hottest air from the house.
REQUIRED VENTING AREA
For proper operation of your AirScape unit, it is CRITICAL that your attic has sufficient venting area;
otherwise the hot air cannot easily escape and creates back-pressure that can substantially reduce the
performance of your new whole house fan.
The “
net-free
” area of a vent is the total vent opening minus the loss caused by the interference of the
screen, louver or grille covering the vent.
The AirScape 2.5/2.5e requires a
MINIMUM of 5
sq ft of "net free" venting area in your attic to allow
for proper exhaust.
This means that it requires the equivalent of a 2 ft by 2
½
ft unobstructed hole. Since most attics have
multiple vents, often of different types, and since most vents are partially obstructed by grilles and/or
bug/animal screens, you’ll need to do some calculations to make sure your venting is sufficient. While
it is our experience that most properly constructed houses have the required venting, not all do. And
because this is so critical to the proper operation of your unit, it is important that you verify it.
Different types of vent designs have different ratios of obstruction caused by grilles and screening and
manufacturers typically publish these numbers. If this information is not available to you, a ratio of 50%
is a good rule of thumb. For example a typical 24" x 24" louver, with a gross area of 4 sq ft, would have
a net free area of 2 sq ft.
Vent
Type
Length
Width
Net Free
Area (NFA%)
Calculation
L x W x NFA / 144
Louver
16”
16”
50 %
= 16 x 16 x 0.5 / 144 = 0.89 sq ft
Ridge Vent
48”
not used
13 %
= 48 x 0.13 / 12 = 0.52 sq ft
Eave Vent
12”
4”
50 %
= 12 x 4 x 0.5 / 144 = 0.16 sq ft
AirScape 2.5/2.5e WHF Installation Manual 02-11 Page
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