48
Table 15 – Maximum Allowable Exposed Vent Lengths in Unconditioned Space Table -- Ft.
Winter
Design
Temp
°F
Unit Size 40,000* BTUH 60,000 BTUH
Uninsulated
3/8-in. Insulation 1/2-in. Insulation
Uninsulated 3/8-in. Insulation 1/2-in. Insulation
Pipe Dia.
in.
1½ 2 2½ 1½ 2 2½ 1½ 2 2½ 1½ 2 2½ 3 1½ 2 2½ 3 1½ 2 2½ 3
20 20 20 20 20 50 45 20 60 50 20 30 30 25 20 75 65 60 20 85 75 65
0 10 5 5 20 25 20 20 30 25 15 15 10 10 20 40 30 25 20 45 40 30
-20 5 20 15 10 20 20 15 10 5 20 25 20 15 20 30 25 20
-40 15 10 5 15 15 10 5 20 15 15 10 20 20 15 10
Winter
Design
Temp
°F
Unit Size 80,000 BTUH
Uninsulated 3/8-in. Insulation 1/2-in. Insulation
Pipe Dia.
in.
1½ 2 2½ 3 4 1½ 2 2½ 3 4 1½ 2 2½ 3 4
20 15 40 40 35 30 15 50 90 75 65 15 50 70 70 70
0 15 20 15 10 5 15 50 45 35 30 15 50 50 40 35
-20 15 10 5 15 35 30 20 15 15 40 30 25 15
-40 10 5 15 25 20 15 5 15 30 25 20 10
Winter
Design
Temp
°F
Unit Size 100,000 BTUH
Uninsulated 3/8-in. Insulation 1/2-in. Insulation
Pipe Dia.
in.
2 2½ 3 4 2 2½ 3 4 2 2½ 3 4
20 20 50 40 35 20 80 95 80 20 80 105 90
0 20 20 15 10 20 55 45 35 20 65 55 45
-20 15 10 5 20 35 30 20 20 45 35 25
-40 10 5 20 25 20 10 20 30 25 15
Winter
Design
Temp
°F
Unit Size 120,000 BTUH 140,000 BTUH
Uninsulated
3/8-in. Insulation 1/2-in. Insulation
Uninsulated 3/8-in. Insulation 1/2-in. Insulation
Pipe Dia.
in.
2½ 3 4 2½ 3 4 2½ 3 4 2½ 3 4 2½ 3 4 2½ 3 4
20 10 50 40 10 75 95 10 75 105 5 55 50 5 65 105 5 65 125
0 10 20 15 10 55 45 10 65 50 5 25 15 5 65 50 5 65 60
-20 10 10 10 35 25 10 45 30 5 10 5 5 45 30 5 50 40
-40 10 5 10 25 15 10 30 20 5 5 5 30 20 5 35 25
Maximum Allowable Exposed V e nt Length in Unconditioned Space (Metric)
Winter
Design
Temp
°C
Unit Size 40,000* BTUH 60,000 BTUH
Uninsulated
3/8-in. Insulation 1/2-in. Insulation
Uninsulated 3/8-in. Insulation 1/2-in. Insulation
Pipe Dia.
mm
38 51 64 38 51 64 38 51 64 38 51 64 76 38 51 64 76 38 51 64 76
-7 6.1 6.1 6.1 6.1 15.2 13.7 6.1 18.3 15.2 6.1 9.1 9.1 7.6 6.1 22.9 19.8 18.3 6.1 25.9 22.9 19.8
-18 3.0 1.5 1.5 6.1 7.6 6.1 6.1 9.1 7.6 4.6 4.6 3.0 3.0 6.1 12.2 9.1 7.6 6.1 13.7 12.2 9.1
-29 1.5 6.1 4.6 3.0 6.1 6.1 4.6 3.0 1.5 6.1 7.6 6.1 4.6 6.1 9.1 7.6 6.1
-40 4.6 3.0 1.5 4.6 4.6 3.0 1.5 6.1 4.6 4.6 3.0 6.1 6.1 4.6 3.0
Winter
Design
Temp
°C
Unit Size 80,000 BTUH
Uninsulated 3/8-in. Insulation 1/2-in. Insulation
Pipe Dia.
mm
38 51 64 76 102 38 51 64 76 102 38 51 64 76 102
-7 4.6 12.2 12.2 10.7 9.1 4.6 15.2 27.4 22.9 19.8 4.6 15.2 21.3 21.3 21.3
-18 4.6 6.1 4.6 3.0 1.5 4.6 15.2 13.7 10.7 9.1 4.6 15.2 15.2 12.2 10.7
-29 4.6 3.0 1.5 4.6 10.7 9.1 6.1 4.6 4.6 12.2 9.1 7.6 4.6
-40 3.0 1.5 4.6 7.6 6.1 4.6 1.5 4.6 9.1 7.6 6.1 3.0
Winter
Design
Temp
°C
Unit Size 100,000 BTUH
Uninsulated 3/8-in. Insulation 1/2-in. Insulation
Pipe Dia.
mm
51 64 76 102 51 64 76 102 51 64 76 102
-7 6.1 15.2 12.2 10.7 6.1 24.4 28.9 24.4 6.1 24.4 32.0 27.4
-18 6.1 6.1 4.6 3.0 6.1 16.8 13.7 10.7 6.1 19.8 16.7 13.7
-29 4.6 3.0 1.5 6.1 10.7 9.1 6.1 6.1 13.7 10.7 7.6
-40 3.0 1.5 6.1 7.6 6.1 3.0 6.1 9.1 7.6 4.6
Winter
Design
Temp
°C
Unit Size 120,000 BTUH 140,000 BTUH
Uninsulated
3/8-in. Insulation 1/2-in. Insulation
Uninsulated 3/8-in. Insulation 1/2-in. Insulation
Pipe Dia.
mm
64 76 102 64 76 102 64 76 102 64 76 102 64 76 102 64 76 102
-7 3.0 15.2 12.2 3.0 22.9 28.9 3.0 22.9 32.0 1.5 16.7 15.2 1.5 19.8 32.0 1.5 19.8 38.1
-18 3.0 6.1 4.6 3.0 16.8 13.7 3.0 19.8 15.2 1.5 7.6 4.6 1.5 19.8 15.2 1.5 19.8 18.3
-29 3.0 3.0 3.0 10.7 7.6 3.0 13.7 9.1 1.5 3.0 1.5 1.5 13.7 9.1 1.5 15.2 12.2
-40 3.0 1.5 3.0 7.6 4.6 3.0 9.1 6.1 1.5 1.5 1.5 9.1 6.1 1.5 35 7.6
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