Lennox ML193UH045P36B Unit Information page 31

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 ma­
terial, 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 41.
Intake and exhaust pipes may be routed either horizontally
through an outside wall or vertically through the roof. In at­
tic or closet installations, vertical termination through the
roof is preferred. Figures 33 through 40 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 34). You may exit the exhaust out the roof
and the intake out the side of the structure (figure 35).
2. Intake and exhaust pipes should be placed as close
together as possible at termination end (refer to il­
lustrations). Maximum separation is 3" (76mm) on roof
terminations and 6" (152mm) on side wall termina­
tions.
NOTE - When venting in different pressure zones, the
maximum separation requirement of intake and ex­
haust pipe DOES NOT apply.
3. On roof terminations, the intake piping should termi­
nate straight down using two 90° elbows (See figure
33).
4. Exhaust piping must terminate straight out or up as
shown. A reducer may be required on the exhaust pip­
ing at the point where it exits the structure to improve
the velocity of exhaust away from the intake piping.
See table 17.
TABLE 17
EXHAUST PIPE TERMINATION SIZE REDUCTION
ML193UH
Exhaust Pipe Size
MODEL
*045 and 070
2" (51mm), 2-1/2" (64mm),
*090
3" (76mm)
110
3" (76mm)
135
*ML193UH-045, -070 and -090 units with the flush mount
termination must use the 1 1/2"accelerator supplied with
the kit.
NOTE - Care must be taken to avoid recirculation of ex­
haust back into intake pipe.
5. On field supplied terminations for side wall exit, ex­
haust 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.
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. See
figure 41.
Inches(mm)
12" (305mm) ABOVE
AVERAGE SNOW
ACCUMULATION
3" (76mm) OR
2" (51mm) PVC
Exhaust
Pipe
Termination
Pipe Size
1-1/2" (38mm)
2" (51mm)
2" (51mm)
Roof T erminated
2" (51mm)
Exhaust Pipe
Page 31
3"(76mm) MAX.
8" (203mm) MIN
PROVIDE SUPPORT
FOR INTAKE AND
EXHAUST LINES
DIRECT VENT ROOF TERMINATION KIT
(15F75 or 44J41)
FIGURE 33
Exiting Exhaust and Intake Vent
(different pressure zones)
Furnace
FIGURE 34
Exiting Exhaust and Intake Vent
(different pressure zones)
Furnace
FIGURE 35
SIZE TERMINATION
PIPE PER TABLE 17.
UNCONDITIONED
ATTIC SPACE
1/2" (13mm) FOAM
INSULATION IN
UNCONDITIONED
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