Proper sized exhaust ducts are essential for proper operation. All elbows should be sweep type. Do not install elbows with a radius less than shown in table below. Exhaust ducts must be assembled so interior surfaces are smooth to reduce accumulation of lint. Do not use sheet metal screws to join vent sections. Improperly sized or assembled ductwork causes excess back pressure which results in slow drying, lint collecting in duct, lint blowing back into room, and increased fire hazard.
Exhaust ducts shall 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 exhaust duct pierces a combustible wall or ceiling, an opening having a diameter of 4 inches (10.2 cm) larger than diameter of exhaust duct shall be provided, with duct centered in opening. When ducts pass through walls, ceilings, floors or partitions, space around the duct shall be sealed with non- combustible material. See Figures 1, 2 and 3.
•Individual Venting
For maximum efficiency and performance, it is preferred to exhaust tumbler(s) individually to outdoors. At no point may cross area of installed venting be less than cross area of exhaust thimble of tumbler.
Maximum allowable length of venting is 14 feet (4.3 m) and two 90° elbows or equivalent. If equivalent length of a duct required for an installation exceeds maximum allowable equivalent length, 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). Table below shows how to determine
equivalent venting:
DUCT | EQUIVALENT LENGTH OF |
DIAMETER | STRAIGHT DUCT |
|
|
6" (15.2 cm) | One 90° elbow = 7' (2.1 m) |
8" (20.3 cm) | One 90° elbow = 9.3' (2.83 m) |
10" (25.4 cm) | One 90° elbow = 11.6' (3.5 m) |
12" (30.5 cm) | One 90° elbow = 14' (4.3 m) |
Equivalent Length (feet) (m) =
1.17 x Duct Diameter (inches) (cm)
Example: A
Equivalent length
=14 feet (4.3 m) + (2) 90° elbows
=14 feet (4.3 m) + 7 feet (2.1 m) + 7 feet (2.1 m)
=28 feet (8.5 m)
With tumbler in operation, airflow at any point in duct must be at least 1200 feet (366 m) per minute to insure that lint remains airborne.
•Collector Venting
While it is preferable to exhaust tumblers individually to outdoors, a main collector duct may be used if it is sized according to Figure 3.
NOTE: This illustration indicates minimum diameters, and should be increased if collector length exceeds 20 feet (6.1 m).
Collector duct may be rectangular in cross section, as long as area is not reduced. Provisions should be made for lint removal and cleaning of collector duct.
Collector duct must be tapered, as shown in Figure 3. Individual tumbler ducts must enter the collector duct at a 45° angle in direction of air flow.
Never connect a tumbler duct at a 90° angle to collector duct. Doing so will cause excessive back pressure, resulting in poor performance. Never connect two tumbler exhaust ducts directly across from each other at point of entry to collector duct.
Collector system must be designed so static back pressure measured 12 inches (30.5 cm) from exhaust thimble does not exceed maximum allowable pressure specified on installation sticker on rear of tumbler. Measured with all tumblers running that are vented into collector.
A tumbler is forced air exhausted and requires provisions for
Manufacturer’s recommended
Example: A tumbler with a rated input of 120,000 BTU/hr (30,240 Kcal) requires 120 in2 (774 cm2) of free opening.
Protective louvers in opening to outdoors can reduce air movement by approximately 40%. Opening must compensate for area taken up by louvers.
32 | M412616 |