Lennox ML193DFE Series Unit Information page 32

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 40.
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. FIGURE 33 through FIGURE 41
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 33). You may exit the
exhaust out the roof and the intake out the side of
the structure (FIGURE 34).
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
(FIGURE 35).
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 16.
TABLE 16
EXHAUST PIPE TERMINATION SIZE REDUCTION
ML193 Model Exhaust Pipe Size
*045 and 070
2" (51mm), 2-1/2" (64mm),
3" (76mm)
*090
*ML193DFE-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. See FIGURE 40. .
NOTE - Care must be taken to avoid recirculation of
exhaust back into intake pipe.
6 - On field supplied terminations, a minimum distance
Exhaust
Pipe
Roof T erminated
Exhaust Pipe
Inches(mm)
Termination
Pipe Size
12" (305mm) ABOVE
AVERAGE SNOW
1-1/2"
ACCUMULATION
(38mm)
2" (51mm)
Page 32
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.
See FIGURE 40.
Exiting Exhaust and Intake Vent
(different pressure zone)
Furnace
FIGURE 33
Exiting Exhaust and Intake Vent
(different pressure zone)
Furnace
FIGURE 34
3"(76mm) MAX.
8" (203mm) MIN
3" (76mm) OR
2" (51mm) PVC
PROVIDE SUPPORT
FOR INTAKE AND
EXHAUST LINES
DIRECT VENT ROOF TERMINATION KIT
(15F75 or 44J41)
FIGURE 35
Inlet Air
(Minimum 12 in.
305 MM) above
grade or snow
accumulation
Inlet Air
(Minimum 12 in.
305 MM) above
grade or snow
accumulation
UNCONDITIONED
ATTIC SPACE