American Dryer Corp. ADH-120 - Manual (Page 20)

16
a. Outside Ductwork Protection
1) To protect the outside end of 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, 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 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: Exhaust back pressure measured by a manometer at each basket (tumbler) exhaust
duct area must not exceed 0.3 inches (0.74 mb) of water column (W.C.).
It is suggested that the ductwork from each dryer not exceed 40 feet (12.2 meters) with no more than three
(3) elbows (including dryer connections and outside exhaust outlets). If the ductwork exceeds 20 feet (6.1
meters) or has numerous elbows, the cross section area of the ductwork must be increased in proportion to
the length and number of elbows in it. In calculating duct size, the cross section area of a square or
rectangular duct must be increased by twenty percent (20%) for each additional 20 feet (6.1 meters). The
diameter of a round exhaust duct should be increased ten percent (10%) for each additional 15 feet (4.57
meters). Each 16-inch (40.64 cm) 90° elbow is equivalent to 36 feet (10.97 meters).