Lennox MERIT Series Installation Instructions Manual page 21

Intake Piping
The ML196DFE furnace may be installed in either direct
vent or non-direct vent applications. In non-direct vent
applications, when intake air will be drawn into the furnace
from the surrounding space, the indoor air quality must be
considered. Guidelines listed in Combustion, Dilution and
Ventilation Air section must be followed.
Follow the next two steps when installing the unit in Direct
Vent applications, where combustion air is taken from out-
doors and flue gases are discharged outdoors. The pro-
vided air intake screen must not be used in direct vent
applications (outdoors).
1 - Use cement to secure the intake pipe to the inlet air
connector.
2 - Route piping to outside of structure. Continue with
installation following instructions given in general
guide lines for piping terminations and intake and
exhaust piping terminations for direct vent sections.
Refe to TABLE 7 for pipe sizes.
Follow the next two steps when installing the unit in Non-
Direct Vent applications where combustion air is taken
from indoors and flue gases are discharged outdoors.
1 - Use field-provided materials and the factory-provided
air intake screen to route the intake piping as shown
in Figure 25. Maintain a minimum clearance of
3" (76mm) around the air intake opening. The air
intake opening (with the protective screen) should
always be directed forward, or sideways.
2 - If intake air is drawn from a ventilated attic (Figure
26) or ventilated crawlspace (Figure 27) the exhaust
vent length must not exceed those listed in TABLE
8. If 3" diameter pipe is used, reduce to 2" diameter
pipe at the termination point to accommodate the
debris screen.
3 - Use cement to secure the intake pipe to the connector,
if desired.
TYPICAL AIR INTAKE PIPE CONNECTIONS
NON−DIRECT VENT APPLICATIONS
NOTE - Air intake screen and elbow may be rotated, so that
screen may be positioned to face forward or to either side.
If this unit is being installed in an application with
combustion air coming in from a space serviced by an
exhaust fan, power exhaust fan, or other device which
may create a negative pressure in the space, take care
when sizing the inlet air opening. The inlet air opening
must be sized to accommodate the maximum volume
of exhausted air as well as the maximum volume of
combustion air required for all gas appliances serviced
by this space.
Page 21
AIR
INTAKE
SCREEN
(Provided)
Figure 25
CAUTION