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108660-01E
10
Figure 9 - Typical B-Vent Configuration
Maintain
Listed
Clearance
12' Min.
45°
6'
8'
12' Min.
60°
45°
Position
Firestop
Position
Firestop
Listed
Vent Cap
Listed Vent Cap
Maintain
Listed
Clearance
Maintain
Listed
Clearance
Maintain
Listed
Clearance
Support
Each
Lateral
At Least
Every
6 Feet
Maintain
Listed
Clearance
EXAMPLE 2
EXAMPLE 1
Maintain
Listed
Clearance
12' Min.
45°
Position
Firestop
Listed
Vent Cap
Maintain
Listed
Clearance
10'
EXAMPLE 3
Example 1 s
hows 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-
lows only one offset in the total system when
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 permitted 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 subfloor, ceil
-
ing joist or an attic overhang. The vent pipe
must terminate vertically into a listed type vent
cap and extend a sufficient height through
an approved roof flashing, roof jack or a roof
thimble. At all points the listed clearances
must be maintained.
Vent terminations must be located in accor-
dance with height and proximity rules of NFPA
Lowest
Discharge
Opening
Listed
Vent Cap
8 Ft. Min.
Roof Pitch x/12
Listed Clearance
12
x
Listed
Gas
Vent
H (Min)
Height
From Roof
Roof Pitch
H (Min.) Ft.
m
Flat to 6/1
1.0
0.30
6/1 to 7/1
1.5
0.38
Over 7/1 to 8/1
1.5
0.46
Over 8/1 to 9/1
.0
0.61
Over 9/1 to 10/1
.5
0.76
Over 10/1 to 11/1
3.5
0.99
Over 11/1 to 1/1
4.0
1.
Over 1/1 to 14/1
5.0
1.5
Over 14/1 to 16/1
6.0
1.83
Over 16/1 to 18/1
7.0
.13
Over 18/1 to 0/1
7.5
.7
Over 0/1 to 1/1
8.0
.44
Figure 10 - B-Vent Terminations
VENTING INSTALLATION
Continued
No. 54 or CAN/CSA B149. These rules apply
to vents at 1" diameter or less and require a
minimum height in accordance with the roof
pitch and a minimum of 8 feet distance from a
vertical wall or obstruction (see Figure 10).
If venting horizontally through a side wall be
-
comes necessary, a listed thimble approved
for use with B-type vent must be used. Check
with your local codes before venting through
a side wall.
