American Dryer Corp. 30 lb. Stacked Models - Manual (Page 12)

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 must
be increased 10 percent for each
additional 15 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 the two (2) elbows. When the duct
work approaches the maximum limits
as noted in this manual, a professional
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 door should be installed at
strategic points in the exhaust duct
work
for periodic inspection and
cleaning.
NOTE: Where the exhaust 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 the
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.
10