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Attic Fans and Whole House Fans
Attic fans can dramatically cut the cost
of your summer air conditioning bill. During long summer afternoons, the
sun beats down on your roof and raises the roof and attic temperature
dramatically higher than the outside air
temperature. While ceiling  insulation reduces heat transfer between
the inside of your house and the attic, it
relies on the attic to serve as a partial
thermal barrier between it and your roof.
As the roof and attic air heat up, they transfer
more heat through the ceiling insulation
to the inside of your house.
Attic fans are an inexpensive solution to
this problem. They can be activated manually
or by a thermostat to quietly ventilate your
attic with the relatively cooler outdoors.
This arrangement makes your roof less thermally
connected to your home and more of a provider
of shade.
Because the fan creates "dynamic"
insulation between the roof and your ceiling,
the fan also allows you to transfer heat
when desired. For example, in cooler weather,
when roof heat (again, in excess of the outside
air temperature) can help warm your home,
the fan can be left off to thermally connect
your roof to your home, enable the attic
to warm, and facilitate the heat transfer
to your ceiling.
In installations in temperate
climates, the
attic fan can also be used to
exhaust air
drawn from the inside of the
house as a "whole
house" fan. In this arrangement,
a one-way,
pressure activated vent in the
ceiling of
the house provides the air to
the attic when
the fan is on. Drawing air out
of the house
creates a gentle suction to draw
breezes
into the home through open doors
and windows.
A similar arrangement can bypass
the attic
and vent directly from the ceiling
to the
outside. |
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