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113344-9 www.amdry.com 15
IMPORTANT: No more than four (4) dryers should be connected to one (1) main common duct.
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 section area for multiple dryer round or square venting. These
figures must be increased 10 square inches (64.52 squares centimeters) when rectangular main ducting is
used, and the ratio of duct width to depth should not be greater than 3-1/2 to 1. These figures must be
increased in proportion if the main duct run to the last dryer to where it exhausts to the outdoors is unusually
long (over 15 feet [4.57 meters]) or has numerous (more than two [2]) elbows in it. In calculating ductwork
size, the cross section area of a square or rectangular duct must be increased twenty percent (20%) for
each additional 15 feet (4.57 meters). The diameter of a round exhaust must be increased ten percent
(10%) for each additional 15 feet (4.57 meters). Each 90º elbow is equivalent to an additional 30 feet
(9.14 meters) and each 45º elbow is equivalent to an additional 15 feet (4.57 meters).
IMPORTANT: For extended ductwork runs, the cross section area of the ductwork can only be
increased to an extent. Maximum proportional ductwork runs,
cannot exceed 15 feet
(4.57 meters) more than the original limitations of 15 feet (4.57 meters) with two (2)
elbows. When the ductwork approaches the maximum limits as noted in this manual,
a professional heating, ventilating, and air-conditioning (HVAC) firm should be
consulted for proper venting information.
IMPORTANT: Exhaust back pressure measured by a manometer at each dryer exhaust duct area
must be no less than 0 and must not exceed 0.3 inches (0.74 mb) of water column
(W.C.).
The ductwork should be smooth inside with 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 ductwork joints must be taped to prevent moisture and lint from escaping into the
building. Inspection doors should be installed at strategic points in the exhaust ductwork for periodic
inspection and cleaning of lint from the ductwork.
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.
Outside Ductwork Protection
To protect the outside end of the horizontal ductwork from the weather, a 90º 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 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.
IMPORTANT: DO NOT use screens, louvers, or caps on the outside opening of the exhaust
ductwork.