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E. EXHAUST REQUIREMENTS
1. General Exhaust Duct Work Information
Exhaust duct work
should be
designed and installed by a qualified professional. Improperly sized duct work
will create excessive back pressure which results in slow drying, increased use of energy, overheating of the
dryer, and shutdown of the burner by the airflow (sail) switches, burner hi-limits, or basket (tumbler) hi-heat
thermostats.
CAUTION:
Dryer
must be
exhausted to the outdoors.
CAUTION:
Improperly sized or installed exhaust dust work can create a potential fire hazard.
The duct work
should be
laid out in such a way that the duct work travels as directly as possible to the outdoors
with as few turns as possible. Single or independent dryer venting is recommended.
When single drying venting is used the length of ductwork from the dryer to the outside exhaust outlet should not
exceed fifteen (15) feet. The minimum diameter of the duct work must be at least 10 inches. Even though the
dryer exhaust duct for gas and electric units is only 8”. The shape of the duct work is not critical so long as the
minimum cross-sectional area is provided. It is suggested that the use of 90º turns
be avoided
; use 30º or 45º
angles instead. The radius of the elbows
should preferably be
1-1/2 times the diameter of the duct. Including
basket (tumbler) and dryer elbow connections or elbows used for outside protection from the weather, no more
than two (2) elbows
should be
used in the exhaust duct run. If more than two (2) elbows are used, the cross
sectional area of the duct work
must be
increased.
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 will
connected.
ALL
duct work joints
must be
taped to prevent moisture and lint from escaping into the building.
The inspection door
should be
installed at strategic points in the exhaust duct work for periodic inspection and
clean-out of lint from the duct work.
IMPORTANT:
Exhaust back pressure measured by a manometer in the exhaust duct
should not
exceed .3 inches of the water column.
IMPORTANT:
Minimum duct work diameter is 10 inches.
IMPORTANT:
Where the exhaust duct work passes through a wall, ceiling, or roof made of
combustible materials, the opening
must be
2 inches larger, all the way around, the duct.
The duct
must be
centered within this opening.
a. Outside Duct Work Protection
1. To protect the outside end of horizontal duct work from the weather, a 90º 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.
