507713-01
Page 16 of 32
Issue 1623
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 (Table 3) 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 (4 and 5) 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:
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 crawl space, attic 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.
14. 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
(2223.1 ).
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
regulator or flue restrictor between the furnace and the
chimney.
21. When connecting this appliance to an existing dedicated
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
requirements, it must be resized.
Table 2
