Lennox MERIT Series Installation Instructions Manual page 26

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 adverse-
ly 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 recommend-
ed. 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 39.
Intake and exhaust pipes may be routed either horizon-
tally through an outside wall or vertically through the roof.
In attic or closet installations, vertical termination through
the roof is preferred. Figures 31 through 39 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 32). You may exit the
exhaust out the roof and the intake out the side of
the structure (figure 33).
2 - 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.
3 - On roof terminations, the intake piping should
terminate straight down using two 90° elbows (See
figure 31).
4 - 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 10.
TABLE 10
Exhaust Pipe Termination Size Reduction
ML195DF Model
*045, *070
*090
110
*ML195DF-045, -070 and -090 units with the flush mount termination must use
the 1-1/2" accelerator supplied with the kit.
5 - 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.
Termination Pipe Size
1-1/2" (38mm)
2" (51mm)
Page 26
NOTE - Care must be taken to avoid recirculation of
exhaust back into intake pipe.
6 - On field supplied terminations, a minimum distance
between the end of the exhaust pipe and the end of
the intake pipe without a termination elbow is 8" and
a minimum distance of 6" with a termination elbow.
3"(76mm) MAX.
Inches(mm)
8" (203mm) MIN
12" (305mm) ABOVE
AVERAGE SNOW
ACCUMULATION
3" (76mm) OR
2" (51mm) PVC
PROVIDE SUPPORT
FOR INTAKE AND
EXHAUST LINES
DIRECT VENT ROOF TERMINATION KIT
(15F75 or 44J41)
FIGURE 31
Exiting Exhaust and Intake Vent
(different pressure zone)
Exhaust
Furnace
Pipe
FIGURE 32
Exiting Exhaust and Intake Vent
(different pressure zone)
Roof T erminated
Exhaust Pipe
Furnace
FIGURE 33
UNCONDITIONED
ATTIC SPACE
Inlet Air
(Minimum 12 in.
305 MM) above
grade or snow
accumulation
Inlet Air
(Minimum 12 in.
305 MM) above
grade or snow
accumulation