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TABLE 7
Maximum Allowable Exhaust Vent Pipe Length (in ft.) Without Insulation In Unconditioned Space For
Winter Design Temperatures Two - Stage High Eciency Furnace
Winter Design
Tempera-
tures1 °F (°C)
Vent Pipe
Diameter
Unit Input Size
045 070 090 110
32 to 21
(0 to -6)
PVC
2
PP
PVC
2
PP
PVC
2
PP
PVC
2
PP
2 in 21 18 33 30 46 42 30 30
2-1/2 in 16 n/a 26 n/a 37 n/a 36 n/a
3 in 12 12 21 21 30 30 29 29
20 to 1
(-7 to -17)
2 in 11 9 19 17 28 25 27 24
2-1/2 in 7 n/a 14 n/a 21 n/a 20 n/a
3 in 2 2 9 9 16 16 14 14
0 to -20
(-18 to -29)
2 in 6 4 12 10 19 16 18 15
2-1/2 in 1 n/a 7 n/a 13 n/a 12 n/a
3 in 1 1 2 2 8 8 7 7
1Refer to 99% Minimum Design Temperature table provided in the current edition of the ASHRAE Fundamentals Handbook.
2 Poly-Propylene vent pipe (PP) by Duravent and Centrotherm.
NOTE - Concentric terminations are the equivalent of 5’ and should be considered when measuring pipe length.
NOTE - Maximum unisulated vent lengths listed may include the termination(vent pipe exterior to the structure) and cannot exceed 5 linear feet or
the maximum allowable intake or exhaust vent length listed in table 5 or 6 which ever is less.
NOTE - If insulation is required in an unconditioned space, it must be located on the pipe closest to the furnace. See gure31.
Conditioned
Space
Unconditioned
Space
Exhaust
Pipe
Intake
Pipe
Conditioned
Space
Pipe Insulation
FIGURE 31
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