American Dryer Corp. AD-230 - Manual (Page 19)

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2. MULTIPLE DRYER (Common) VENTING
If it is not feasible to provide separate exhaust ducts for each dryer, ducts from individual dryers may be
channeled into a "common main duct." The individual ducts should enter the bottom or side of the main
duct at an angle not more than 45º in the direction of the airflow. The main duct should be tapered, with the
diameter increasing before each individual 8-inch duct is added.
IMPORTANT: No more than eight (8) dryers should be connected to one main common duct.
NOTE: Refer to the illustration on page 16 for examples of multiple dryer (common) venting.
The main duct may be any shape so long as the minimum cross-sectional area is provided. The illustration
on page 16 shows the minimum cross-sectional area for multiple dryer venting. These figures must be
increased in proportion if the main duct run from the last dryer to where it exhausts to the outdoors is
unusually long (over 20 feet) or has numerous elbows (more than two [2]) in it.
IMPORTANT: For extended duct work runs, the cross section area of the duct work can only be
increased to an extent. Maximum proportional duct work runs cannot exceed 20
feet more than the original limitations of 20 feet with two (2) elbows. When the duct
work approaches the maximum limits as noted in this manual, a professional HVAC
firm should be consulted for proper venting information.
IMPORTANT: Exhaust back pressure measured by a manometer at each basket (tumbler) exhaust
duct area should not exceed 0.3 inches W.C. (water column).
The duct work should be smooth inside with no projections from sheet metal screws or other obstructions
which will collect lint. When adding ducts, the duct to be added should overlap the duct to which it is to be
connected. ALL duct work joints must be taped to prevent moisture and lint from escaping into the
building. Also, inspection doors should be installed at strategic points in the exhaust duct work for periodic
inspection and cleaning.
NOTE: Where the exhaust passes through a wall, ceiling, or roof made of combustible materials, the
opening must be 2-inches larger (all the way around) than the duct. The duct must be
centered within this opening.
To protect the outside end of the horizontal duct work from the weather, a 90º elbow bent downward
should be installed where the exhaust exits the building. If the exhaust duct work 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 between the duct opening and
nearest obstruction.