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IMPORTANT: Exhaust back pressure measured by a manometer in the exhaust duct must not
exceed 0.3 inches (0.74 mb) of water column (W.C.).
IMPORTANT: When the exhaust ductwork passes through a wall, ceiling, or roof made of
combustible materials, the opening must be 2-inches (5.08 cm) larger than the duct
(ALL the way around). The duct must be centered within this opening.
a. Outside Ductwork Protection
1) To protect the outside end of the horizontal ductwork from the weather, a 90° elbow bent downward
should be installed where the exhaust exits the building. If the exhaust ductwork travels vertically
up through the roof, it should be protected from the weather by using a 180° turn to point the
opening downward. In either case, allow at least twice the diameter of the duct between the duct
opening and the nearest obstruction.
IMPORTANT: DO NOT use screens or caps on the outside opening of the exhaust ductwork.
2. Single Dryer Venting
Where possible, it is suggested to provide a separate exhaust duct for each dryer. The exhaust duct should
be laid out in such a way that the ductwork travels as directly as possible to the outdoors with as few turns
as possible. It is suggested that the use of 90° turns in ducting be avoided; use 30° and/or 45° angles instead.
The shape of the exhaust ductwork is not critical so long as the minimum cross section area is provided.
IMPORTANT: Minimum duct size for a dryer is 16-inches (40.64 cm) for a round duct or 14-1/2” x
14-1/2” (36.83 cm x 36.83 cm) for a square duct. THE DUCT SIZE MUST NOT
BE REDUCED ANYWHERE DOWNSTREAM OF THE DRYER.
IMPORTANT: Exhaust back pressure measured by a manometer in the exhaust duct must not
exceed 0.3 inches (0.74 mb) of water column.
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