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18
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 air flow and should be spaced at least 46-1/8" apart.
The main duct should be tapered, with the diameter increasing before each individual 14-inch (minimum for
gas dryers or 72 Kw electric dryers) or 16-inch (minimum for steam dryers) duct is added.
IMPORTANT: The AD-115 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 four (4) dryers should be connected to one main common duct.
The main duct may be any shape or cross sectional area, so long as the minimum cross section area is
provided. The illustrations on pages 20 and 21 show the minimum cross section area for multiple
dryer round or square venting. These figures must be increased 10 square inches when rectangular main
ducting is used, and the ratio of duct width to depth should not be greater than 3-1/2 to 1. These figures
must be increased in proportion if the main duct run to the last dryer to where it exhausts to the outdoors is
unusually long (over twenty [20] feet) or has numerous elbows (more than two [2]) in it. In calculating duct
work size, the cross section area of a square or rectangular duct must be increased twenty (20) percent for
each additional twenty (20) feet. The diameter of a round exhaust must be increased ten (10) percent for
each additional twenty (20) feet. Each 90° elbow is equivalent to an additional fifteen (15) feet.