American Dryer Corp. Gas/HSI & Steam ID-120 - Manual (Page 21)

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IMPORTANT: Exhaust back pressure measured by a manometer at each basket (tumbler) exhaust
duct area must be no less than 0 and must not exceed 0.3 inches (0.74 mb) of water
column (W.C.).
a. Ducting (Horizontal and Vertical)
1) For single dryer horizontal ducting the minimum duct size is 16-inches (40.64 cm) in diameter, the
duct run should not have more than one (1) elbow (including outside protection), and must not
exceed 40 feet (12.2 meters) in total length. With single dryer vertical ducting, the minimum duct
size is 18-inches (45.72 cm) in diameter, the duct run should not have more than three (3) elbows
(including outside protection), and must not exceed 20 feet (6.1 meters) in total length.
IMPORTANT: When the ductwork approaches the maximum limits as 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.