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If B vent or an insulated flexible vent pipe cannot be used
as liners, the chimney must be rebuilt to accommodate
one of these methods or some alternate approved meth
od must be found to vent the appliance.
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 G23(X) series units. The chimney
passageway must be checked periodically to ensure that
it is clear and free of obstructions.
General Venting Requirements
All G23(X) furnaces must be vented in accordance with
the methods outlined in these instructions.
1 - Vent diameter recommendations and maximum runs
allowed are found in the provided venting tables.
2 - In no case should the vent or vent connector diame
ter be less than the diameter specified in the pro
vided venting tables.
3 -
For 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
maxi
mum vent capacity
. The flow area of the vertical
vent, however, shall not exceed 7 arial the flow area
of the listed appliance categorized vent area, draft
hood outlet area or flue collar area unless designed
in accordance with approved engineering methods.
4 -
For multiple appliance vents:
The flow area of the
largest section of vertical vent or chimney shall not
exceed 7 arial the smallest listed appliance catego
rized vent area, flue collar area or drafthood outlet
area unless designed according to with approved en
gineering methods.
5 - The entire length of single wall metal vent connector
shall be readily accessible for inspection, cleaning,
and replacement.
6 - Single appliance venting configurations with zero lat
eral lengths are assumed to have no elbows in the
vent system. See tables 3 and 4. 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 percent
(0.90 x maximum listed capacity).
7 - The common venting tables 5, 6, 7, and 8 were gen
erated using a maximum horizontal vent connector
length of 1-1/2 feet (.46 mm) for each inch (25 mm) of
connector diameter as follows in table 2:
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)
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 ca
pacity). The horizontal length of the offset shall not
exceed 1 1/2 feet (.46 mm) 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. The vent connector should be routed to
the vent using 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 to
ward the appliance.
11- Vent connectors shall be firmly attached to 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
doublewall type B vent material or material having
equivalent insulation qualities.
13- All venting pipe passing through floors, walls, and
ceilings must be installed with the listed clearance to
combustible materials and be fire stopped according
to local 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 operation under positive pressure such as
Category III or IV venting systems.