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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 lat
eral lengths (table 30) 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 exam
ple 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 ca
pacity).
8 - The common venting tables (4, 5 and) were generated
using a maximum horizontal vent connector length of
1-1/2 feet (.46 m) for each inch (25 mm) of connector
diameter as follows:
TABLE 2
Connector Diameter
inches (mm)
Maximum Horizontal
Connector Length feet (m)
3 (76)
4-1/2 (1.37)
4 (102)
6 (1.83)
5 (127)
7-1/2 (2.29)
6 (152)
9 (2.74)
7 (178)
10-1/2 (3.20)
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 com
plete the job. Route the vent connector to the vent us
ing 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 ap
pliances must be located in or pass through a crawl
space, attic or other areas which may be cold, that por
tion of the vent connector shall be constructed of listed
double‐wall type B vent material or material having
equivalent insulation qualities.
14 - All venting pipe passing through floors, walls, and ceil
ings must be installed with the listed clearance to com
bustible materials and be fire stopped according to lo
cal codes. In absence of local codes, refer to NFGC
(Z223.1).
15 - No portion of the venting system can extend into, or pass
through any circulation air duct or plenum.
16 - Vent connectors serving Category I appliances shall
not be connected to any portion of mechanical draft
systems operating under positive pressure such as
Category III or IV venting systems.
17 - If vent connectors are combined prior to entering the
common vent, the maximum common vent capacity
listed in the common venting tables must be reduced by
10%, the equivalent of one 90° elbow (0.90 x maximum
common vent capacity).
18 - The common vent diameter must always be at least as
large as the largest vent connector diameter.
19 - In no case, shall the vent connector be sized more than
two consecutive table size diameters over the size of
the draft hood outlet or flue collar outlet.
20 - Do not install a manual damper, barometric draft regu
lator or flue restrictor between the furnace and the
chimney.
21 - When connecting this appliance to an existing dedi
cated or common venting system, you must inspect the
venting system's general condition and look for signs
of corrosion. The existing vent pipe size must conform
to these instructions and the provided venting tables. If
the existing venting system does not meet these re
quirements, it must be resized.
