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TABLE 16
Maximum Allowable Exhaust Vent Pipe Length (in ft.) Without Insulation In Unconditioned Space For
Winter Design Temperatures Single - Stage High Efficiency Furnace
Winter Design
Temperatures
1
°F (°C)
Vent Pipe
Diameter
Unit Input Size
045 070 090 110 135
32 to 21
(0 to -6)
PVC
2
PP PVC
2
PP PVC
2
PP PVC
2
PP PVC
2
PP
2 in. 26 24 44 41 44 44 24 24 N/A N/A
2-1/2 in. 18 N/A 32 N/A 50 N/A 58 N/A N/A N/A
3 in. 14 12 26 23 38 33 55 49 60 53
20 to 1
(-7 to -17)
2 in 16 15 28 26 40 37 24 24 N/A N/A
2-1/2 in. 12 N/A 20 N/A 30 N/A 44 N/A N/A N/A
3 in. 9 8 16 14 26 23 32 28 40 35
0 to -20
(-18 to -29)
2 in. 10 9 20 18 30 28 24 24 N/A N/A
2-1/2 in. 8 N/A 14 N/A 20 N/A 32 N/A N/A N/A
3 in. 4 3 10 8 16 14 26 23 30 26
1
Refer to 99% Minimum Design Temperature table provided in the current edition of the ASHRAE Fundamentals Handbook.
2
Poly-Propylene vent pipe (PP)
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 14 or 15 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 figure30.
FIGURE 30
Conditioned
Space
Unconditioned
Space
Exhaust
Pipe
Intake
Pipe
Conditioned
Space
Pipe Insulation
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