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Fig. 20: Direct Vent Horizontal Thru-Wall Venting (Category III)
12"
36" MIN.
12" MIN.
6"
VENT CAP
VENT PIPE
COMBUSTION AIR
FILTER
BOILER
UNIT
INTAKE
VENT
INTAKE
VENT
Model
No.
Appliance
Category
Certified
Venting
Material
Vent Size
(inches)
Max.
Venting
Length
(feet)
Combustion
Air Intake
Pipe
Material
Air Inlet
Size
(inches)
Max. Air
Intake
Length
(feet)
122
III
Stainless
Steel
(Gas Tight)
4
40
Subtract 10
ft per
elbow,
Max. two
elbows
Galvanized
Steel
PVC
ABS
CPVC
5
40
Subtract 10
ft per
elbow,
Max. two
elbows
162
202
242
5
322 6
Table L: Horizontal Thru-Wall Venting