American Dryer Corp. 30 lb. Stacked Models - Manual (Page 11)

If the duct work exceeds 20 feet or has
numerous elbows, the cross section
area of the duct work must be
increased in proportion to its length or
number of elbows in it. In calculating
duct size, the cross section area of a
square or rectangular duct must be
increased 20 percent for each
additional 20 feet. The diameter of a
round exhaust should be increased 10
percent for each additional 20 feet.
Each 90 degree elbow is equivalent to
an additional 15 feet and each 45
degree elbow, an additional 10 feet.
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 run cannot exceed 20 feet more
than the original limitations of 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.
The 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. Also,
inspection doors should be installed
at strategic points in the exhaust duct
work
for periodic inspection and
cleaning.
NOTE: Where the exhaust duct passes
through a wall, ceiling, or roof made
of combustible materials, the opening
must be two (2) inches larger (all the
way around) than the duct. The duct
must be centered within this opening.
To protect the outside end of
horizontal duct work from the weather,
a 90 degree elbow bent downward
should be installed where the exhaust
exits the building (see illustration on
page 11). If the exhaust duct work
travels vertically up through the roof,
it should be protected from the
weather by using a 180 degree turn to
point
the opening downward (see
illustration on page 11). In either case,
allow at least twice the diameter of the
duct between the duct opening and
nearest obstruction.
IMPORTANT: Do not use screens or
caps on the outside of opening of
exhaust duct work.
2. 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” (see illustration on page 11). The
individual ducts should enter the
bottom or side of the main duct at an
angle not more than 45 degrees in the
direction of airflow. The main duct
should be tapered, with the diameter
increasing before each individual duct
is added. The cross section area
should be 60 square inches for each
eight (8) inch duct added.
IMPORTANT: No more than four (4)
dryers total should be connected to
one main common duct.
The main duct may be any shape or
cross section area, so long as the
minimum cross section area is
provided. The illustration on page 11
shows
the minimum cross section
area for multiple dryer venting. These
figures
must be increased in
proportion if the main duct runs from
the last dryer to where it exhausts to
the outdoors is unusually long (over
20 feet) or has numerous elbows
(more than two {2}) in it.