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IMPORTANT: For extended ductwork runs, the cross section area of the duct can only be increased
to an extent. 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.
c. Outside Ductwork Protection
1) To protect the outside end of the horizontal ductwork from the weather, a 90° 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 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 opening of the exhaust
ductwork.
3. Multiple Dryer (Common) Venting
a. Horizontal 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 46-1/8"
(117.16 cm) apart. The main duct should be tapered, with the diameter increasing before each individual
14-inch (35.56 cm) duct is added.
IMPORTANT: No more than four (4) dryers should be connected to one (1) main common duct
IMPORTANT: It is recommended that exhaust or booster fans not be used in the exhaust ductwork
system.
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