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W415-0788 / A / 09.22.09
Simple venting configurations.
See graph to determine the required vertical rise V
T
for the
required horizontal run H
T
.
REQUIRED
VERTICAL
RISE IN
FEET V
T
HORIZONTAL VENT RUN PLUS OFFSET IN FEET H
T
For vent configurations requiring more than two 90° elbows (top exit) or one 90° elbow (rear exit),
the following formulas apply:
Formula 1: H
T
< 3 V
T
Formula 2: H
T
+ V
T
< 40 feet
Example 7:
V
1
= 2 FT
V
2
= 1 FT
V
3
= 1.5 FT
V
T
= V
1
+ V
2
+ V
3
= 2 + 1 + 1.5 = 4.5 FT
H
1
= 6 FT
H
2
= 2 FT
H
R
= H
1
+ H
2
= 6 + 2 = 8 FT
H
O
= .03 (four 90° elbows - 90°)
= .03 (360° - 90°) = 8.1 FT
H
T
= H
R
+ H
O
= 8 + 8.1 = 16.1 FT
H
T
+ V
T
= 16.1 + 4.5 = 20.6 FT
Formula 1: H
T
< 3.5 V
T
3.5 V
T
= 3 x 4.5 = 13.5 FT
16.1 < 13.5
Since this formula is not met, this vent configuration is unacceptable.
Formula 2: H
T
+ V
T
< 40 FT
16.1 < 13.5
Since only formula 2 is met, this vent configuration is unacceptable and a new fireplace location or vent configuration will
need to be established to satisfy both formulas.
90°
V
1
H
1
H
2
The shaded area within the lines represents acceptable
values for H
T
and H
T
90°
90°
90°
V
3
0
5101520
10
20
3
25 30
19
V
2
(H
T
) > (V
T
)
18.2_2
FIGURE 3.11c
FIGURE 3.11d