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b. 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 opening of the 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 55-3/4 inches
(141.61 cm) apart. The main duct should be tapered, with the diameter increasing before each individual
16-inch (40.64 cm) duct is added.
a. Multiple Dryer Venting
1) In case of multiple (common) dryer venting, the distance from the last dryer to the outside exhaust
outlet must not exceed 20 feet (6.1 meters), and not have more than one (1) elbow (including
outside protection).
2) The minimum size of the duct from each dryer into the common duct is 16-inches (40.64 cm), and
must not have more than one (1) elbow. The total duct run from the dryer to the common duct
must not exceed 15 feet (4.57 meters) in length.
IMPORTANT: The ML-145 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.
The main duct may be any shape or cross-sectional area, so long as the minimum cross section area
is provided. The illustrations on page 20 show the minimum cross-sectional area for multiple
dryer round or square venting. These figures must be increased 10 square inches (64.51 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 exceeds the maximum limits noted.
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
(6.1 meters) more than the original limitations of 20 feet (6.1 meters) with two (2)
elbows. 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.
IMPORTANT: Exhaust back pressure measured by a manometer at each dryer exhaust duct area
must not exceed 0.3 inches of water column (W.C.) - 0.74 mb.