American Dryer Corp. Gas- DSI/Steam ML-82 II - Manual (Page 19)

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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.).
NOTE: 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 horizontal ductwork from the weather, a 90º elbow bent downward
should be installed where the exhaust exits the building. If the ductwork travels vertically up
through the roof, it should be protected from the weather by using a 180º turn to point the opening
downward. In either case, allow at least twice the diameter of the duct opening and the nearest
obstruction.
IMPORTANT: DO NOT use screens, louvers, 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 the 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: For a dryer that is vented horizontally, the minimum duct size for a gas dryer is
14-inches (35.56 cm) for a round duct or 12-1/2” (31.75 cm) for a square duct.
THE DUCT SIZE MUST NOT BE REDUCED ANYWHERE
DOWNSTREAM OF THE DRYER.