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TABLE 7
Maximum Allowable Exhaust Vent Pipe Length 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)
2 in. 26 44 44 24 N/A
2−1/2 in. 18 32 50 58 N/A
3 in. 14 26 38 55 60
20 to 1
(−7 to −17)
2 in 16 28 40 24 N/A
2−1/2 in. 12 20 30 44 N/A
3 in. 9 16 26 32 40
0 to −20
(−18 to −29)
2 in. 10 20 30 24 N/A
2−1/2 in. 8 14 20 32 N/A
3 in. 4 10 16 26 30
1
Refer to 99% Minimum Design Temperature table provided in the current edition of the ASHRAE Fundamentals Handbook.
NOTE − Maximum unisulated vent lengths listed cannot exceed the maximum allowable intake or exhaust vent length listed in table 5.
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