Lennox MERIT Series Installation Instructions Manual page 21

Intake Piping
The ML195DF furnace may be installed in either direct
vent or non-direct vent applications. In non-direct vent ap-
plications, 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 Di-
rect Vent applications, where combustion air is taken from
outdoors and flue gases are discharged outdoors. The
provided 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.
Refer to table 7 for pipe sizes.
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.
FIGURE 25
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.
AIR
INTAKE
SCREEN
(Provided)
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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 a sheet metal screw to secure the intake pipe to
the connector, if desired.
CAUTION
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.
EQUIPMENT IN CONFINED SPACE
(Inlet Air from Ventilated Attic and Outlet Air to Outside)
Roof Terminated
Exhaust Pipe
NOTE-The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645mm
hour of the total input rating of all equipment in the enclosure.
FIGURE 26
Ventilation Louvers
Inlet Air
(Minimum
12 in.(305mm) Above
attic floor)
*Intake Debris
Screen
(Provided)
Furnace
2
per 1.17kW) per