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6 − Single appliance venting configurations with zero lat-
eral lengths (tables 5 and 6), are assumed to have no
elbows in the vent system. For all other vent configura-
tions, the vent system is assumed to have two 90° el-
bows. 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 percent (0.90 x maximum
listed capacity).
7 − The common venting tables (7, 8, 9, and 10) were gen-
erated 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 4
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)
8 − 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.
9 − 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.
10 − 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.
11 − Vent connectors shall be firmly attached to the furnace
flue collars by screws or other approved means, ex-
cept vent connectors of listed type B vent material
which shall be assembled according to the manufac-
turer’s instructions. Joints between sections of single
wall connector piping shall be fastened by screws or
other approved means.
12 − When the vent connector used for Category I ap-
pliances must be located in or pass through a crawl-
space 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.
13 − 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).
14 − No portion of the venting system can extend into, or pass
through any circulation air duct or plenum.
15 − 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.
16 − 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 percent, the equivalent of one 90° elbow (0.90 x
maximum common vent capacity).
17 − The common vent diameter must always be at least as
large as the largest vent connector diameter.
18 − 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.
19 − Do not install a manual damper, barometric draft regu-
lator or flue restrictor between the furnace and the
chimney.
20 − 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
for the USA, and the appropriate venting tables in the
standards of CSA B149 Natural Gas and Propane
Installation Codes for Canada. If the existing venting
system does not meet these requirements, it must be
resized.
