507712-01
Page 14 of 36
Issue 1642
SINGLE appliance venting of a fan assisted furnace into
a tile lined masonry chimney (interior or outside wall) is
prohibited. The chimney must first be lined with either
type B1 vent or an insulated single wall flexible vent
lining system which has been sized according to the
provided venting tables and the vent pipe manufacturer’s
instructions.
IMPORTANT
A fan assisted furnace may be commonly vented into an
existing lined masonry chimney if the following conditions
are met:
• The chimney is currently serving at least one draft
hood-equipped appliance.
• The vent connectors and chimney are sized according
to the provided venting tables.
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 B 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, draft
hood 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, draft hood 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 (Tables 4 and 5) 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 (6, 7, 8 and 9) 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
complete the job. Route the vent connector to the vent
using the shortest possible route.
