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FIGURE 23
Common Venting Using Tile-Lined Interior Masonry Chimney and Combined Vent Connector
MINIMUM LENGTH = AS SHORT AS PRACTICAL.
FOR MAXIMUM LENGTH SEE NOTE TO LEFT
INTERIOR TILE-LINED
MASONRY CHIMNEY
NOTE - the chimney must be properly
sized per provided venting tables or
lined with listed metal lining system.
PERMANENTLY
SEALED FIREPLACE
OPENING
VENT
CONNECTOR
NOTE- Refer to provided venting
tables for installations.
FURNACE
OTHER
APPLIANCE
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 4) 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 tables (5 and 6) 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 3
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.
