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113409-2 www.amdry.com 15
IMPORTANT: Exhaust back pressure measured by a manometer at each tumbler exhaust duct area must be
no less than 0 and must not exceed 0.6 inches (1.48 mb) of water column (W.C.).
It is suggested that the ductwork from each dryer not exceed 15 feet (4.57 meters) with no more than three (3)
elbows (excluding dryer connections). If the ductwork exceeds 15 feet (4.57 meters) or has numerous elbows, the
cross-sectional area of the ductwork must be increased in proportion to the length and number of elbows in it. In
calculating duct size, the cross-sectional 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 duct should be increased ten
percent (10%) for each additional 10 feet (3.04 meters). Each 90º elbow is equivalent to an additional 40 feet
(12.19 meters), and each 45º elbow is equivalent to an additional 20 feet (6.09 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 three (3) 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.
ALL ductwork 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 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.