Lennox SLP98DFV - Page 22

Page 22
TABLE 8
Maximum Allowable Vent Pipe Length (in ft.) Without Insulation In Unconditioned Space
For Winter Design Temperatures Modulating High Efciency Furnace
Winter Design
Temperatures1
°F (°C)
Vent Pipe
Diameter
Unit Input Size
070 090 110 135
32 to 21
(0 to -6)
PVC
2
PP PVC
2
PP PVC
2
PP PVC
2
PP
2 in. 11 9 14 12 18 15
N/A N/A
2-1/2 in 7
N/A
10 N/A 12 N/A
3 in.
N/A
6 6 8 8 13 13
20 to 1
(-7 to -17)
2 in. 6 4 8 6
N/A N/A
2-1/2 in.
N/A N/A N/A N/A
3 in.
0 to -20
(-18 to -29)
2 in.
2-1/2 in.
3 in.
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 uninsulated 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 7 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 gure24.
Conditioned
Space
Unconditioned
Space
Exhaust
Pipe
Intake
Pipe
Conditioned
Space
Pipe Insulation
FIGURE 24