April2017

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

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

"The main objective of these fans is to cool the attic in the warm summer months."

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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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