MAXIDRY MAXI120, Installation Manual, Page: 12 / 30

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The exhaust ductwork should be laid out in such a way
that the ductwork travels as directly as possible to the
outdoors with as few turns as possible. Single or
independent dryer venting is recommended. When
single dryer venting is used, the ductwork from the dryer
to the outside exhaust outlet must not exceed 20 feet
(6.09 meters). In the case of multiple (common) dryer
venting, the distance from the last dryer to the outside
exhaust outlet must not exceed 20 feet (6.09 meters).
The shape of the ductwork is not critical as long as the
minimum cross section area is provided. It is suggested
that the use of 90° turns in ducting be avoided; use 30°
and/or 45° angles instead. The radius of the elbows
should preferably be 1-1/2 times the diameter of the duct.
Excluding tumbler dryer elbow connections or elbows
used for outside protection from the weather, no more
than two elbows should be used in the exhaust duct
run. If more than two elbows are used, the cross section
area of the ductwork must be increased in proportion to
number of elbows added.
IMPORTANT: It is recommended that exhaust booster
fans not be used in the exhaust ductwork system.
NOTE: As per the National Fuel Gas Code, “Exhaust
ducts for type 2 clothes dryers shall be constructed of
sheet metal or other noncombustible material. Such
ducts shall be equivalent in strength and corrosion
resistance to ducts made of galvanized sheet steel not
less than 26 gauge (0.0195-inches [0.5 mm]) thick.”
All ductwork should be smooth inside with no projections
from sheet metal screws or other obstructions, which
will collect lint. When adding ducts, the ducts to be added
should overlap the duct to which it is connected. All
ductwork joints must be taped to prevent moisture and
lint from escaping into the building. Additionally,
inspection doors should be installed at strategic points
in the exhaust ductwork for periodic inspection and
cleaning of lint from the ductwork.
To protect the outside end of the horizontal ductwork
from the weather, a 90° elbow bent downward should
be installed where the exhaust exits the building. If the
ductwork 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 (i.e., roof or ground
level).
IMPORTANT: Exhaust back pressure measured by a
manometer at the dryer exhaust duct area must be no
less than 0 and must not exceed 0.3 in WC (0.75 mb,
75 Pa).
NOTE: When the exhaust ductwork passes through a
wall, ceiling, or roof made of combustible materials,
the opening must be 2-inches (5.08 cm) larger than
the duct (all the way around). The duct must be
centered within this opening.
To protect the outside end of the horizontal ductwork
from the weather, a 90° elbow bent downward should
be installed where the exhaust exits the building. If the
exhaust ductwork 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.
Single Dryer Venting
When possible, it is suggested to provide a separate exhaust
duct for each dryer. The exhaust duct should be laid out in such
a way that the ductwork travels as directly as possible to the
outdoors with as few turns as possible. It is suggested that the
use of 90° turns in ducting be avoided; use 30° and/or 45° angles
instead. The shape of the exhaust ductwork is not critical as long
as the minimum cross section area is provided.
IMPORTANT: Minimum duct size for a gas, electric, or steam
dryer with a vertical run and not more than three elbows
(including dryer connection and outside outlets) is 16-inches
(40.64 cm) for a round duct or 14-1/2” by 14-1/2” (36.83 cm by
36.83 cm) for a square duct. Duct size must not be reduced
anywhere downstream of dryer.
Exhaust back pressure measured by a manometer at each
tumbler exhaust duct area must be no less than 0 and must not
exceed 0.3 in WC (0.75 mb, 75 Pa).
It is suggested that the ductwork from each dryer (minimum
14-inches [35.56 cm]) not exceed 20 feet (6.09 meters) with no
more than three elbows (including dryer connections and outside
exhaust outlets). If the ductwork exceeds 20 feet (6.09 meters)
or has numerous elbows, the cross section area of the ductwork
must be increased in proportion to the length and number of
elbows in it. In calculating duct size, the cross section area of a
square or rectangular duct must be increased by twenty percent
for each additional 20 feet (6.09 meters). The diameter of a round
exhaust duct should be increased ten percent for each additional
15 feet (4.57 meters). Each 14-inch (35.56 cm) 90° elbow is
equivalent to 30 feet (9.14 meters) and each 16-inch (40.64 cm)
90° elbow is equivalent to 36 feet (10.97 meters).
IMPORTANT: Do not use screens, louvers, or caps on the
outside opening of the exhaust ductwork.