Lennox MERIT Series Installation Instructions Manual page 23

Maximum Allowable Exhaust Vent Pipe Length (in ft.)
Winter Design Temperatures Single - Stage High Efficiency Furnace
Winter Design
Temperatures °F (°C)
1
32 to 21
(0 to -6)
20 to 1
(-7 to -17)
0 to -20
(-18 to -29)
1
Refer 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 or 8 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 Figure 28.
3
Vent length in the table is equivalent length. Each elbow is equivalent to 5ft of straight pipe and should be included when measuring total length.
TABLE 9
Vent Pipe
Diameter
045
PVC
1-1/2 in 20
2 in 18
2-1/2 in 13
3 in 9
1-1/2in. 15
2 in 9
2-1/2 in 5
3 in 1
1-1/2 in 10
2 in 5
2-1/2 in 1
3 in N/A
Conditioned
Space
3 Without Insulation In Unconditioned Space For
Unit Input Size
070
PP PP
PVC
2 2
N/A 20 N/A
16 31 28
N/A 24 N/A
9 18 18
N/A 20 N/A
8 18 16
N/A 13 N/A
1 8 8
N/A 15 N/A
3 12 10
N/A 7 N/A
N/A 2 2
Conditioned
Space
Pipe Insulation
Unconditioned
Space
Figure 28
Page 23
090
PP
PVC PVC
2
N/A N/A N/A
50 48 30
42 N/A 36
35 35 29
N/A N/A N/A
32 29 27
24 N/A 20
19 19 14
N/A N/A N/A
22 19 18
15 N/A 12
10 10 7
Exhaust
Pipe
Intake
Pipe
110
PP
2
N/A
30
N/A
29
N/A
24
N/A
14
N/A
15
N/A
7