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M414545
21
• Collector Venting
While it is preferable to exhaust tumblers individually
to the outdoors, a main collector duct may be used if it
is sized accordingly. Refer to Figure 5. This
illustration indicates minimum diameters, and should
be increased if the collector length exceeds 20 feet
(6.1 m). The collector duct may be rectangular in cross
section, as long as the area is not reduced. Provisions
should be made for lint removal and cleaning of the
collector duct.
The collector duct must be tapered. Refer to Figure 5.
The individual tumbler ducts must enter the collector
duct at a 45° angle in the direction of airflow. Never
connect a tumbler duct at a 90° angle to the 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 the point of entry to the collector duct.
The collector system must be designed so the static
back pressure measured 12 inches (30.5 cm) from the
exhaust thimble does not exceed the maximum
allowable pressure specified on the installation sticker
on the rear of the tumbler. This must be measured with
all tumblers running that are vented into the collector.
MAKE-UP AIR
A tumbler is forced air exhausted and requires provisions
for make-up air to replace the air exhausted by the
tumbler.
IMPORTANT: Do not obstruct the flow of
combustion and ventilation air.
Recommended make-up air opening to the outside is
144 inches
2
(928 cm
2
).
At a minimum, the National Fuel Gas Code requires
tumblers to have at least one square inch (6.5 sq. cm)
of opening for every 1000 BTU/hr. of input rating for
proper combustion.
Example: A tumbler with a rated input of 120,000
BTU/hr. requires 120 square inches of free
opening.
The additional opening recomended by the
manufacturer is required for optimum drying and
reliability.
Protective louvers in the opening to the outdoors can
reduce air movement by approximately 40 percent. The
opening must compensate for the area taken up by the
louvers.
The make-up air openings for a room containing
tumbler(s) and/or gas fired hot water heater or other
gravity vented appliances must be increased sufficiently
to prevent downdrafts in any of the vents when all
tumblers are in operation. Do not locate gravity vented
appliances between tumbler(s) and make-up air
openings. If it is necessary to duct make-up air to the
tumbler(s), increase the area of the duct work by 25
percent to compensate for any restriction in air
movement.