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16
IMPORTANT: For extended duct work runs, the cross section area of the duct work 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 one (1) elbow for
horizontal runs and three (3) elbows for vertical runs. When the duct work 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 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 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
the nearest obstruction.
IMPORTANT: DO NOT use screens 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 45º in the direction of air flow and should be spaced at least 46 inches apart. The
main duct should be tapered, with the diameter increasing before each individual duct (16 inch minimum) is
added.
IMPORTANT: The ML-96HS is shipped with a 16-inch butterfly damper in the drum. The damper must
be installed at each dryer duct.
IMPORTANT: No more than three (3) dryers should be connected to main common duct.
The main duct may be any shape so long as the minimum cross sect is provided. The illustration on page 18
shows 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 ration 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
from the last dryer to where it exhausts to the outdoors is unusually long (over twenty [20] feet) or has
numerous (more than two [2] elbows 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
90º elbow is equivalent to an additional thirty-six (36) feet and each 45º elbow is equivalent to an additional
fifteen (18) feet.