17
IMPORTANT:
For extended duct work runs, the cross section area of the duct work can only be
increased to an extent. When the duct work approaches the maximum limits 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 work 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 the 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 180º 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 airflow and
should be
spaced at least 38-1/4 (97.15 cm)
apart. The main duct
should be
tapered, with the diameter increasing before each individual duct (14-inch
[35.56 cm] minimum for gas models and 16-inch [40.64 cm] minimum for steam models) is added.
IMPORTANT:
No more than four (4) dryers
should be
connected to one main common duct.
The main duct may be any shape so long as the minimum cross-sectional area is provided. The
illustration
on
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 squares 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 15 feet [4.57 meters]) 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 percent (20%) for
each additional 15 feet (4.57 meters). The diameter of a round exhaust
must be
increased ten percent
(10%) for each additional 15 feet (4.57 meters). Each 90º elbow is equivalent to an additional 30 feet (9.14
meters) and each 45º elbow is equivalent to an additional 15 feet (4.57 meters).
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