507324-01B
Page 15 of 32
Issue 1809
If type B1 double wall vent is used inside a chimney, no
other appliance can be vented into the chimney. The outer
wall of type B1 vent pipe must not be exposed to flue
products. A type B1 vent or masonry chimney liner shall
terminate above the roof surface with a listed cap or a listed
roof assembly according to the terms of their respective
listings and the vent manufacturer’s instructions.
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. The chimney passageway must be
checked periodically to ensure that it is clear and free of
obstructions.
Do not install a manual damper, barometric draft regulator,
or flue restrictor between the furnace and the chimney.
Never connect a Category I appliance to a chimney that is
servicing a solid fuel appliance. If a fireplace chimney flue
is used to vent this appliance, the fireplace opening must
be permanently sealed.
A type B1 or listed chimney lining system that passes
through an unused masonry chimney flue is not considered
to be exposed to the outdoors.
General Venting Requirements
Vent all furnaces according to these instructions:
1. Vent diameter recommendations and maximum
allowable piping runs are found in the provided venting
tables.
2. In no case should the vent or vent connector diameter
be less than the diameter specified in the provided
venting tables.
3. The minimum vent capacity determined by the sizing
tables must be less than the low fire input rating and
the maximum vent capacity must be greater than the
high fire input rating.
4. 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 maximum vent
capacity. The flow area of the vertical vent, however,
shall not exceed 7 times the flow area of the listed
appliance categorized vent area, drafthood outlet
area or flue collar area unless designed according to
approved engineering methods.
5. Multiple appliance vents - The flow area of the largest
section of vertical vent or chimney shall not exceed 7
times the smallest listed appliance categorized vent
area, drafthood outlet area or flue collar area unless
designed according to approved engineering methods.
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 Table 4 and Table 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:
Table 2.
Connector Diameter
in. (mm)
Maximum Horizontal
Connector Length
ft. (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
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 double wall type B vent material or material
having equivalent insulation qualities.