American Dryer Corp. MLG32PD3 - Manual (Page 18)

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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.
IMPORTANT: No more than eight (8) dryers should be connected to one (1) main common duct.
NOTE: Refer to the illustration on page 15 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 15 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 [6.1 meters]) or has numerous elbows (more than one [1]) in it.
IMPORTANT: For extended duct work runs, the cross-sectional area of the duct work can only be
increased to an extent. Maximum proportional duct work runs cannot exceed 20 feet
(6.1 meters) more than the original limitations of 20 feet (6.1 meters) with one (1)
elbow. When the duct work approaches the maximum limits as noted in this manual, a
professional heating, venting, and air-conditioning (HVAC) firm must be consulted for
proper venting information.
IMPORTANT: Exhaust back pressure measured by a manometer at the dryer’s exhaust duct area
must not exceed 0.3 inches of water column (W.C.) - 0.74 mb - when both baskets
(tumblers) are operating.
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: When the exhaust duct work 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.
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.