American Dryer Corp. MLG-130DR (HSI) - Manual (Page 22)

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NOTE: Where the exhaust duct passes through a wall, ceiling, or roof made of combustible materials,
the opening must be 2-inches (5.08 cm) 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 45° in the direction of the flow and should be spaced at least 48-3/4 inches
(123.83 centimeters) apart. The main duct should be tapered with the diameter increasing before each
individual 12-inch (30.48 cm) - minimum for each dryer - duct is added.
IMPORTANT: The ML-130DR 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 (1) 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 illustration on the bottom of page 19 shows the minimum cross section area for multiple
dryer round or square venting. These figures must be increased 10 square inches (64.52 square centimeters)
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 20 feet [6.09 meters]) or has numerous elbows (more than
two [2]) in it. In calculating duct work size, the cross-sectional area of a square or rectangular duct must
be increased twenty percent (20%) for each additional 20 feet (6.09 meters). The diameter of a round
exhaust must be increased ten (10) percent for each additional 20 feet (6.09 meters). Each 90° elbow is
equivalent to an additional 30 feet (9.14 meters) and each 45° elbow is equivalent to an additional 15 feet
(4.57 meters).
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 20
feet (6.09 meters) more than the original limitations of 20 feet (6.09 meters) 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.
IMPORTANT: Exhaust back pressure measured by a manometer in the exhaust duct should not
exceed 0.3 inches of water column (0.74 mb).