Vent pipe and air inlet pipe size depends on input rating of the furnace. See
Table following for sizing and materials based on model size and input rating.
Minimum length is 5 ft.
Vent and Combustion Air Pipe Sizing for Separated Combustion
Model
Size
Input (Btuh)
Combustion Air Inlet
Flue Exhaust (Vent Pipe)
Max. Vent
Pipe
Length
Diameter
Material
Diameter
Material
090
90,000
3"
PVC
3"
PVC
35’
135
135,000
3"
PVC
3"
PVC
35'
180
180,000
4"
PVC
4"
PVC
35'
225
225,000
4"
PVC
4"
PVC
35'
270
270,000
6"
Galv. Steel (or) SS
4"
PVC
35'
315
315,000
6”
Galv. Steel (or) SS
4”
PVC
25'
360
360,000
6”
Galv. Steel (or) SS
4”
PVC
25'
400
400,000
6”
Galv. Steel (or) SS
(2) 4”
PVC
(2) 35'
450
450,000
8”
Galv. Steel (or) SS
(2) 4”
PVC
(2) 35'
540
540,000
8”
Galv. Steel (or) SS
(2) 4”
PVC
(2) 35'
630
630,000
10”
Galv. Steel (or) SS
(2) 4”
PVC
(2) 25'
720
720,000
10”
Galv. Steel (or) SS
(2) 4”
PVC
(2) 25'
