American Dryer Corp. Gas- DSI/Steam ML-82 II - Manual (Page 20)

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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 15 feet (4.57 meters) with no more than two
(2) elbows (excluding dryer connections and outside exhaust outlets). If the ductwork exceeds 15 feet
(4.57 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 15 feet (4.57
meters). The diameter of a round exhaust duct should 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. When the ductwork approaches the maximum limits noted in
this manual, a professional heating, venting, 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.
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.