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126754-01B
10
VENTING INSTALLATION
at 60° or greater. The total vertical height in
this example represents the minimum height
of 8 feet and therefore the allowable lateral
is 6 feet when the 75% rule applies. If the
lateral length must exceed 75% then the
system must be sized in accordance with the
Category I venting tables.
Example 2:
Shows a multiple offset each at
45° of inclination. Multiple offsets are permit
-
ted if they do not exceed 45° of inclination. The
total lengths of the two offsets are not required
to meet the 75% allowable rule.
Example 3:
Shows a single offset at 45° of
inclination and therefore the lateral length at
10 feet of offset does not have to meet the
75% rule.
In each case the offsets must be supported
and firestops must be positioned wherever
the vent must pass through a sub-floor, ceiling
joist or an attic overhang. The vent pipe must
terminate vertically into a listed type vent cap
and extend a sufficient height through an ap
-
proved roof flashing, roof jack or a roof thimble
(38FST recommended). At all points the listed
clearances must be maintained.
Vent terminations must be located in ac
-
cordance with height and proximity rules of
NFPA No. 54. These rules apply to vents at
12" diameter or less and require a minimum
height in accordance with the roof pitch and
a minimum of 8 ft. distance from a vertical
wall or obstruction (see Figure 11, page 11).
A B-type venting system must be connected
to appliance for venting to the outside of
building.
The following section is provided as a guide
to a standard B-type vent installation.
Standing codes requirements concerning B-
type vent installations may vary within your
state, province or local codes jurisdiction.
Therefore, it is recommended that you check
with your local building codes for specific
requirements or in absence of local codes,
follow Section 7.0 of the current
National Fuel
Gas Code ANSI Z223.1/NFPA 54
.
This gas appliance must be vented to the
outdoors only and may not be terminated into
an attic space or into a chimney flue servicing
a solid-fuel burning appliance.
This appliance may be vented through a
manufactured chimney system or a masonry
chimney using a B-vent adapter or a chim
-
ney liner system if all are listed, inspected
and approved by local codes and/or building
authorities.
The examples shown in Figure 10, page 11
are typical of most B-vent installations and
codes practices.
Example 1:
Shows the minimum allowable
system height and lateral offset for a 60° or
greater inclination. Code specifies that offsets
at 60° or greater are considered horizontal
and must follow the 75% rule for lateral to
total vertical system height. Codes also al
-
low only one offset in the total system when
f i r e - p a r t s . c o m
