18
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| (HT) > (VT) |
Simple venting configurations. | See graph to determine the required vertical rise VT for the |
| required horizontal run HT. |
REQUIRED VERTICAL RISE IN FEET VT
19 | 20 |
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| 10 |
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3 |
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| 0 | 5 | 10 | 15 | 20 | 25 | 30 |
HORIZONTAL VENT RUN PLUS OFFSET IN FEET HT
The shaded area within the lines represents acceptable
values for HT and VT
For vent configurations requiring more than two 90° elbows the following formulas apply:
Formula 1: HT < 3VT
Formula 2: HT + VT < 40 feet
Example 2:
V1 = 2 FT
V2 = 1 FT
V3 = 1.5 FT
VT = V1 + V2 + V3 = 2 + 1 + 1.5 = 4.5 FT H1 = 6 FT
H2 = 2 FT
HR = H1 + H2 = 6 + 2 = 8 FT
HO = .03 (four 90° elbows - 90°) = .03 (360° - 90°) = 8.1 FT
HT = HR + HO = 8 + 8.1 = 16.1 FT HT + VT = 16.1 + 4.5 = 20.6 FT
90° 
90°
H2
V | H1 | V |
| 1 | 2 |
90°
V3 |
90°
Formula 1: | HT | < 3VT |
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| 3VT | = 3 x 4.5 = 13.5 FT |
| 16.1 > 13.5 | ||
Since this formula is not met, this vent configuration is unacceptable.
Formula 2: | HT + VT < 40 feet |
| 20.6 < 40 |
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.
18.1_2A
