Direct vent installations require both a combustion air intake and a vent/flue pipe. The pipes may be run horizontally and exit
through the side of the building or run vertically and exit through the roof of the building. The pipes may be run through an existing
unused chimney; however, they must extend a minimum of 12 inches above the top of the chimney. The space between the pipes
and the chimney must be closed with a weather tight, corrosion resistant flashing. Both the combustion air intake and a vent/flue
pipe terminations must be in the same atmospheric pressure zone. Refer to Vent/Flue and Combustion Air Pipe - Termination
Locations or Concentric Vent Termination for specific details on termination construction. For details concerning connection of pipes
to the furnace, refer to the Vent/Flue Pipe and Combustion Pipe - Standard Furnace Connections or Alternate Furnace Connections.
Refer to the following table for applicable length, elbows, and
pipe diameter for construction of the vent/flue and combus-
tion air intake pipe systems of a direct vent (dual pipe) in-
stallation. The number of elbows tabulated represents the
number of elbows and/or tees in each (Vent/Flue & Combus-
tion Air Intake) pipe. Elbows and/or tees used in the termi-
nations must be included when determining the number of
elbows in the piping systems.
If the combustion air intake pipe is to be installed above a
finished ceiling or other area where dripping of condensate
will be objectionable, insulation of the combustion air pipe
may be required.
Use 1/2" thick closed cell foam insulation such as
Armaflex™ or Insultube™ where required.
The vent/flue and combustion air pipes may terminate verti-
cally, as through a roof, or horizontally, as through an outside
Vertical pipe terminations should be as shown in the following
figure. Refer to Vent/Flue Pipe and Combustion Pipe - Ter-
mination Locations for details concerning location restric-
tions. The penetrations through the roof must be sealed
tight with proper flashing such as is used with a plastic
Vent & Combustion Air Intake Measurements for Stan-
dard Horizontal Terminations (Dual Pipe)
Center to center = 10" min / 24" max.
Vertical separation: 0" - 24"
Vent termination from wall = 8" min / 12" max.
Combustion air intake from wall = 6" max.
Vent and intake clearance to ground or anticipated snow
level = 12" min.
If more than one direct vent furnace is to be installed
vertically through a common roof top, maintain the same
minimum clearances between the exhaust vent and air
intake terminations of adjacent units as with the exhaust
vent and air intake terminations of a single unit.
90º OR 45°
Standard Horizontal Terminations (Dual Pipe)
Alternate Horizontal Vent Termination (Dual Pipe)
12" MIN. TO GRADE OR
3" - 24"
12" MIN. ABOVE