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Exhaust Requirements
43
70458301ENR6
NOTE: Exhaust ducts must be constructed of sheet
metal or other noncombustible material. Such
ducts must be equivalent in strength and corrosion
resistance to ducts made of galvanized sheet steel
not less than 0.0195 inches (0.495 mm) thick.
Where the exhaust duct pierces a combustible wall or
ceiling, the opening must be sized per local codes. The
space around the duct may be sealed with noncombustible
material. Refer to
Figure 17
.
IMPORTANT: For best performance provide an
individual exhaust duct for each tumble dryer. Do
not install a hot water heater in a room containing
tumble dryers. It is better to have the water heater
in a separate room with a separate air inlet.
Individual Venting
For maximum efficiency and performance, it is
preferred to exhaust tumble dryer(s) individually to the
outdoors.
IMPORTANT: At no point may the cross sectional
area of installed venting be less than the cross
sectional area of the exhaust outlet of the tumble
dryer.
The exhaust duct must be designed so the static back
pressure measured 12 inches (305 mm) from the
exhaust outlet does not exceed the maximum
allowable pressure specified on the installation sticker
on the rear of the tumble dryer.
NOTE: Static back pressure must be measured
with the tumble dryer running.
The maximum allowable length venting is 14 feet
(4.3 m) and two 90° elbows or equivalent. If the
equivalent length of a duct required for an installation
exceeds the maximum allowable equivalent length, the
diameter of a round duct must be increased by 10% for
each additional 20 feet (6.1 m). Cross section area of a
rectangular duct must be increased by 20% for each
additional 20 feet (6.1 m). Refer to
Table 3
to
determine equivalent venting.
NOTE: The maximum length of a flexible metal
duct must not exceed 7.87 ft. (2.4 m) as required to
meet UL2158, clause 7.3.2A.
Example: A 12 inch (305 mm) diameter duct’s
equivalent length of 14 feet (4.3 m) of duct and two
90° elbows is:
Equivalent Length
= 14 ft. (4.3 m) + (2) 90° elbows
= 14 ft. (4.3 m) + 14 ft. (4.3 m) + 14 ft. (4.3 m)
= 42 ft. (12.8 m)
With the tumble dryer in operation, airflow at any
point in the duct should be at least 1200 feet/min.
(366 m/min.) to ensure that lint remains airborne. If
1200 feet/min. (366 m/min.) per minute cannot be
maintained, schedule monthly inspections and
cleaning of the ductwork.
WARNING
Improperly sized or assembled ductwork
causes excess back pressure which
results in slow drying, lint collecting in
the duct, lint blowing back into the room,
and increased fire hazard.
W355
Duct
Diameter
Equivalent Length of Rigid
Straight Duct
8 in. (203 mm)
10 in. (254 mm)
12 in. (305 mm)
14 in. (356 mm)
16 in. (406 mm)
18 in. (457 mm)
One 90° elbow = 9.3 ft. (2.83 m)
One 90° elbow = 11.6 ft. (3.5 m)
One 90° elbow = 14 ft. (4.3 m)
One 90° elbow = 16 ft. (4.9 m)
One 90° elbow = 18.7 ft. (5.7 m)
One 90° elbow = 21 ft. (6.4 m)
Equivalent Length (meter) = 1.17 x Duct Diameter (mm)
Table 3
