Allied A96US2V - Maximum Exhaust Vent Lengths for Specific Installations

507404-02 Page 21 of 80Issue 1448
Table 5C
Maximum Allowable Exhaust Vent Lengths with Furnace Installed in a Closet or Basement Using Ventilated
Attic or Crawl Space for Intake Air in Feet
* Size intake and exhaust pipe length separately. Values in table are for intake OR Exhaust, not combined total. Both Intake and Exhaust must
be same pipe size.
* Additional vent pipe and elbows used to terminate the vent pipe outside the structure must be included in the total vent length calculation.
Standard Termination at Elevation 0 - 4500 
Number
of 90°
Elbows
Used
2" Pipe 2-1/2" Pipe 3" Pipe
Model Model Model
45 70 90 110 135 45 70 90 110 135 45 70 90 110 135
1 66 51 29 9 n/a 95 95 73 38 n/a 113 112 93 93 89
2 61 46 24 4 90 90 68 33 108 107 88 88 84
3 56 41 19 n/a 85 85 63 28 103 102 83 83 79
4 51 36 14 80 80 58 23 98 97 78 78 74
5 46 31 9 75 75 53 18 93 92 73 73 69
6 41 26 4 70 70 48 13 88 87 68 68 64
7 36 21 n/a 65 65 43 8 83 82 63 63 59
8 31 16 60 60 38 3 78 77 58 58 54
9 26 11 55 55 33 n/a 73 72 53 53 49
10 21 6 50 50 28 68 67 48 48 44
Standard Termination at Elevation 4500 - 10,000 
Number
of 90°
Elbows
Used
2" Pipe 2-1/2" Pipe 3" Pipe
Model Model Model
45 70 90 110 135 45 70 90 110 135 45 70 90 110 135
1 66 51 29 n/a n/a 95 95 73 38 n/a 113 112 93 93 89
2 61 46 24 90 90 68 33 108 107 88 88 84
3 56 41 19 85 85 63 28 103 102 83 83 79
4 51 36 14 80 80 58 23 98 97 78 78 74
5 46 31 9 75 75 53 18 93 92 73 73 69
6 41 26 4 70 70 48 13 88 87 68 68 64
7 36 21 n/a 65 65 43 8 83 82 63 63 59
8 31 16 60 60 38 3 78 77 58 58 54
9 26 11 55 55 33 n/a 73 72 53 53 49
10 21 6 50 50 28 68 67 48 48 44