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and pull air from within the attic and
exhaust it to the exterior. These fans
also require openings in the soffit to
allow cool exterior air to be pulled
into the attic. The attic fans are often
hard wired, but newer solar powered
fans are becoming more common
ATTIC FANS...
from page 20.
on the market. Because they are
powered by a motor, these fans are
referred to as an “active” ventilation
system because they actively pull air
out of the attic.
Some of the attic fans have a tem-
perature sensor that turns them on
and off and sometimes, particularly in
older models, they are connected to
an on/off switch. The main objective
of these fans is to cool the attic in the
warm summer months. While some
fans have a sensor that measures the
relative humidity in the attic, most do
not and therefore it is quite rare that
the fans operate in the colder, winter
months.
Attic fans are typically installed high
on the roof in an effort to pull out the
warmest air located at the ridge of the
attic. When an attic fan is installed
with upper passive ventilation compo-
nents, such as a ridge vent or static
dome vent, the fan will pull the most
air from the closest source. Rather than
pulling air from the soffits, the attic
fans will pull air from the ridge vent
or nearby static dome vent. This cre-
ates a short cycling effect that results
in pockets within the attic space that
are not properly ventilated. The strong
pull of air into the ridge or static vent
located near the attic fan can also
pull rain and moisture into the attic.
For this reason, industry standards
CONT I NU E S ON PAGE 24
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"The main objective
of these fans is
to cool the attic
in the warm
summer
months."