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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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