American Dryer Corp. MD-170 - Manual (Page 22)

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IMPORTANT: For extended duct work runs, the cross section area of the duct can only be increased
to an extent. Maximum proportional duct work runs cannot exceed twenty (20) feet
more than the original limitations of twenty (20) feet with two (2) elbows. When the
duct work approaches the maximum limits as noted in this manual, a professional
heating venting air conditioning (HVAC) firm should be consulted for proper venting
information.
ALL 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.
Inspection doors should be installed at strategic points in the exhaust duct work for periodic inspection and
clean-out of lint from the duct work.
NOTE: Where the exhaust duct passes through a wall, ceiling, or roof made of combustible materials,
the opening must be 2-inches larger (all the way around) than the duct. The duct must be
centered within this opening.
a. Outside Duct Work Protection
1) To protect the outside end of horizontal duct work from the weather, a 90° 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 180° 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 of opening of exhaust duct
work.
3. 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 45° in the direction of airflow and should be spaced at least 55-1/2 inches
apart. The main duct should be tapered, with the diameter increasing before each individual 18-inch
duct is added.
IMPORTANT: The MD-170 is not provided with a back draft damper. When exhausted into a
multiple (common) exhaust line, a back draft damper must be installed at each dryer
duct.
IMPORTANT: No more than three (3) dryers should be connected to one (1) main common duct.