Lennox MERIT ML195UH Installation Instructions Manual page 24

Maximum Allowable Exhaust Vent Pipe Length (in ft.) Without Insulation In Unconditioned Space For
Winter Design
Temperatures1 °F
(°C)
32 to 21
(0 to -6)
20 to 1
(-7 to -17)
0 to -20
(-18 to -29)
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 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 figure30.
Winter Design Temperatures Single - Stage High Efficiency Furnace
Vent Pipe
Diameter
045
PP
PVC
2
2 in 18 16
2-1/2 in 13 N/A
3 in 9
2 in 9
2-1/2 in 5
3 in N/A
2 in 5 N/A
2-1/2 in N/A
3 in N/A
Conditioned
Space
TABLE 7
Unit Input Size
070
PP
PVC PVC
2
31 28 50
24 N/A 42
9 18 18 35
8 18 16 32
13 N/A 24
8 8 19
12 10 22
7 N/A 15
N/A N/A 10
Conditioned
Space
Pipe Insulation
Unconditioned
Space
FIGURE 30
Page 24
090 110
PP PP
PVC
2 2
48 30 30
N/A 56 N/A
35 47 47
29 30 30
N/A 34 N/A
19 26 26
19 30 27
N/A 22 N/A
10 16 16
Exhaust
Pipe
Intake
Pipe
135
PP
PVC
2
N/A N/A
N/A N/A
52 52
N/A N/A
N/A N/A
30 30
N/A N/A
N/A N/A
18 18