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Details of Intake and Exhaust Piping
Terminations for Direct Vent Installations
NOTE: In Direct Vent installations, combustion air is taken
from outdoors and flue gases are discharged to outdoors.
NOTE: Flue gas may be slightly acidic and may adversely
affect some building materials. If any vent termination is
used and the flue gasses may impinge on the building
material, a corrosion-resistant shield (minimum 24 inches
square) should be used to protect the wall surface. If the
optional tee is used, the protective shield is recommended.
The shield should be constructed using wood, plastic,
sheet metal or other suitable material. All seams, joints,
cracks, etc. in the affected area should be sealed using an
appropriate sealant. See Figure 34.
Intake and exhaust pipes may be routed either horizontally
through an outside wall or vertically through the roof. In
attic or closet installations, vertical termination through the
roof is preferred. Figure 23 through Figure 34 show typical
terminations.
1.
Intake and exhaust terminations are not required to be
in the same pressure zone. You may exit the intake on
one side of the structure and the exhaust on another
side (Figure 23). You may exit the exhaust out the roof
and the intake out the side of the structure (Figure 24).
Exhaust
Furnace
Pipe
Figure 24. Exiting Exhaust and Intake Vent
(no common pressure zone)
Roof T erminated
Exhaust Pipe
Furnace
Figure 25. Exiting Exhaust and Intake Vent
(no common pressure zone)
1.
2.
3.
Inlet Air
Minimum 12 in.
(305MM) above
grade or snow
accumulation
Inlet Air
* Units with the flush mount termination must use the 1-1/2"
Minimum 12 in.
accelerator supplied with the kit
(305MM) above
grade or snow
Table 12. Exhaust Pipe Termination Size Reduction
accumulation
4.
Page 30
Intake and exhaust pipes should be placed as close
together as possible at termination end (refer to
illustrations). Maximum separation is 3" (76MM)
on roof terminations and 6" (152MM) on side wall
terminations.
NOTE: When venting in different pressure zones,
the maximum separation requirement of intake and
exhaust pipe DOES NOT apply.
On roof terminations, the intake piping should terminate
straight down using two 90° elbows (Figure 25).
3" (76MM) MIN.
Inches (MM)
8" (203MM) MIN
12" (305MM) ABOVE
AVERAGE SNOW
ACCUMULATION
3" (76MM) OR
2" (51MM) PVC
PROVIDE SUPPORT
FOR INTAKE AND
EXHAUST LINES
Figure 23. Direct Vent Roof Termination
Exhaust piping must terminate straight out or up as
shown. A reducer may be required on the exhaust
piping at the point where it exits the structure to
improve the velocity of exhaust away from the intake
piping. See Table 12.
NOTE: Care must be taken to avoid recirculation of
exhaust back into intake pipe.
Model
Exhaust Pipe Size
070
2" (51 mm), 2-1/2"
(64 mm),
3" (76 mm)
090
110
3" (76 mm)
On field-supplied terminations for side wall exit,
exhaust piping may extend a maximum of 12 inches
(305MM) for 2" PVC and 20 inches (508MM) for 3"
(76MM) PVC beyond the outside wall. Intake piping
should be as short as possible. See Figure 34.
SIZE PER EXHAUST PIPE
TERMINATION SIZE
REDUCTION TABLE
UNCONDITIONED
ATTIC SPACE
1/2" (13MM) FOAM
INSULATION IN
UNCONDITIONED
SPACE
Termination Pipe
Size
1-1/2" (38 mm)
2" (51 mm)
31-5000727 Rev. 0
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