17
90º OR 45°
ELBOW
12" MIN. TO GRADE OR
HIGHEST ANTICIPATED
SNOW LEVEL
6” MAX
4” MIN
Standard Horizontal Terminations (Dual Pipe)
Figure 16
DIRECT VENT (DUAL PIPE) PIPING
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.
VENT/FLUE & COMBUSTION AIR PIPE LENGTHS & DIAMETERS
Refer to the following table for applicable length, elbows,
and pipe diameter for construction of the vent/flue and
combustion air intake pipe systems of a direct vent (dual
pipe) installation. The number of elbows tabulated represents
the number of elbows and/or tees in each (Vent/Flue &
Combustion Air Intake) pipe. Elbows and/or tees used in
the terminations 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.
VENT/FLUE AND COMBUSTION AIR PIPE TERMINATIONS
The vent/flue and combustion air pipes may terminate
vertically, as through a roof, or horizontally, as through an
outside wall.
Vertical pipe terminations should be as shown in the following
figure. Refer to Vent/Flue Pipe and Combustion Pipe -
Termination Locations for details concerning location
restrictions. The penetrations through the roof must be
sealed tight with proper flashing such as is used with a plastic
plumbing vent.
VENT & COMBUSTION AIR INTAKE MEASUREMENTS FOR STANDARD
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 clearnace to ground or anticipated snow level
= 12” min.
Alternate Horizontal Vent Termination (Dual Pipe)
Figure 17
90°
ELBOWS
12" MIN. ABOVE
HIGHEST ANTICIPATED
SNOW LEVEL
3” - 24”
Combustion Air Intake may also be snorkeled to obtain 12” min ground clearance.
Alternate Vent Termination Above Anticipated Snow Level
(Dual Pipe)
Figure 18
90°
ELBOWS
12" MIN. AB OVE
HIGHEST ANTICIPATED
SNOW LEVEL
3”-24” BETWEEN PIPES
VENT/INTAKE TERMINATIONS FOR INSTALLATION OF MULTIPLE
DIRECT VENT FURNACES
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.
If more than one direct vent furnace is to be installed
horizontally through a common side wall, maintain the
clearances as in the following figure. Always terminate all
exhaust vent outlets at the same elevation and always
terminate all air intakes at the same elevation.
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