Lennox SL280UHNV Installation Instructions Manual page 15

A type B1 vent or masonry chimney liner shall terminate
above the roof surface with a listed cap or a listed roof as-
sembly according to the terms of their respective listings
and the vent manufacturer's instructions.
When inspection reveals that an existing chimney is not
safe for the intended purpose, it shall be rebuilt to conform
to nationally recognized standards, lined or relined with
suitable materials, or replaced with a gas vent or chimney
suitable for venting SL280UHNV series units. The chim-
ney passageway must be checked periodically to ensure
that it is clear and free of obstructions.
Do not install a manual damper, barometric draft regulator,
or flue restrictor between the furnace and the chimney.
Never connect a Category I appliance to a chimney that is
servicing a solid-fuel appliance. If a fireplace chimney flue
is used to vent this appliance, the fireplace opening must
be permanently sealed.
A type B or listed chimney lining system that passes
through an unused masonry chimney flue is not consid-
ered to be exposed to the outdoors.
general Venting Requirements
Vent all SL280UHNV furnaces according to these instruc-
tions:
1 - Vent diameter recommendations and maximum
allowable piping runs are found in the provided
venting tables
2 - In no case should the vent or vent connector
diameter be less than the diameter specified in the
provided venting tables.
3 - The minimum vent capacity determined by the
sizing tables must be less than the low fire input
rating and the maximum vent capacity must be
greater than the high fire input rating.
4 - Single appliance vents - If the vertical vent or tile-
lined chimney has a larger diameter or flow area than
the vent connector, use the vertical vent diameter to
determine the minimum vent capacity and the vent
connector diameter to determine the maximum vent
capacity. The flow area of the vertical vent, however,
shall not exceed 7 times the flow area of the listed
appliance categorized vent area, drafthood outlet
area or flue collar area unless designed according
to approved engineering methods.
5 - Multiple appliance vents - The flow area of the
largest section of vertical vent or chimney shall
not exceed 7 times the smallest listed appliance
categorized vent area, drafthood outlet area or flue
collar area unless designed according to approved
engineering methods.
6 - The entire length of single wall metal vent connector
shall be readily accessible for inspection, cleaning,
and replacement.
7 - Single appliance venting configurations with zero
lateral lengths are assumed to have no elbows in
the vent system. For all other vent configurations,
the vent system is assumed to have two 90°
elbows. For each additional 90° elbow or equivalent
(for example two 45° elbows equal one 90° elbow)
beyond two, the maximum capacity listed in the
venting table should be reduced by 10% (0.90 x
maximum listed capacity).
8 - The common venting TABLE 4 and TABLE 5
were generated using a maximum horizontal vent
connector length of 18" (457 mm) for each inch (25
mm) of connector diameter as follows:
Connector Diameter
inches (mm)
3 (76)
4 (102)
5 (127)
6 (152)
7 (178)
9 - If the common vertical vent is offset, the maximum
common vent capacity listed in the common venting
tables should be reduced by 20%, the equivalent
of two 90° elbows (0.80 x maximum common vent
capacity). The horizontal length of the offset shall
not exceed 1-1/2 feet (.46 m) for each inch (25 mm)
of common vent diameter.
10 - The vent pipe should be as short as possible with
the least number of elbows and angles required to
complete the job. Route the vent connector to the
vent using the shortest possible route.
11 - A vent connector shall be supported without any
dips or sags and shall slope a minimum of 1/4 inch
(6.4 mm) per linear foot (305 mm) of connector,
back toward the appliance.
12 - Vent connectors shall be firmly attached to the
furnace flue collar by self-drilling screws or other
approved means, except vent connectors of listed
type B vent material which shall be assembled
according to the manufacturer's instructions. Joints
between sections of single wall connector piping
shall be fastened by screws or other approved
means.
13 - When the vent connector used for Category I
appliances must be located in or pass through
a crawlspace, attic or other areas which may
be cold, that portion of the vent connector shall
be constructed of listed double-wall type B vent
material or material having equivalent insulation
qualities.
Page 15
TABLE 2
Maximum Horizontal
Connector Length feet (m)
4-1/2 (1.37)
6 (1.83)
7-1/2 (2.29)
9 (2.74)
10-1/2 (3.20)