Filters; Duct System; Venting; Connector 0 - Lennox G40UH Series Installation Instructions Manual

Filters

This unit is not equipped with a filter or rack. A field−pro-
vided high−velocity filter is required for the unit to operate
properly. Table 1 lists recommended filter sizes.
A filter must be in place whenever the unit is operating.
TABLE 1
Furnace Furnace
Cabinet Size
Side Return
14−1/2" 16 X 25 X 1 (1)
17−1/2" 16 X 25 X 1 (1)
21" 16 X 25 X 1 (1)
24−1/2" 16 X 25 X 1 (2)

Duct System

Use industry-approved standards to size and install the
supply and return air duct system. This will result in a quiet
and low-static system that has uniform air distribution.
NOTE − Do not operate the furnace with an external static
pressure that exceeds 0.5 inches w.c. Higher external stat-
ic pressures may cause erratic limit operation.
Supply Air Plenum
If the furnace is installed without a cooling coil, a removable
access panel must be installed in the supply air duct. The
access panel should be large enough to permit inspection
(either by smoke or reflected light) of the heat exchanger
for leaks after the furnace is installed. The furnace access
panel must always be in place when the furnace is operat-
ing and it must not allow leaks into the supply air duct sys-
tem.
Return Air Plenum
Return air must not be drawn from a room where this
furnace, or any other gas appliance (ie., a water heat-
er), is installed. When return air is drawn from a room, a
negative pressure is created in the room. If a gas ap-
pliance is operating in a room with negative pressure, the
flue products can be pulled back down the vent pipe and
into the room. This reverse flow of the flue gas may result
in incomplete combustion and the formation of carbon
monoxide gas. This toxic gas might then be distributed
throughout the house by the furnace duct system.
In upflow applications, the return air can be brought in
through the bottom or either side of the furnace. If a furnace
with bottom return air is installed on a platform, make an air-
tight seal between the bottom of the furnace and the plat-
form to ensure that the unit operates properly and safely.
Use fiberglass sealing strips, caulking, or equivalent seal-
ing method between the plenum and the furnace cabinet to
ensure a tight seal. If a filter is installed, size the return air
duct to fit the filter frame.
Filter Size
Bottom Return
14 X 25 X 1 (1)
16 X 25 X 1 (1)
20 X 25 X 1 (1)
24 X 25 X 1 (1)
Page 12

Venting

A 4−inch diameter flue transition is factory-installed on the
combustion air inducer outlet of all models. Modifying or
removing the flue transition will cause the unit to oper-
ate unsafely and will void the unit certification. The
vent connector does not require insulation.
The combustion air inducer may be rotated clockwise or
counterclockwise by 90° to allow for vertical vent dis-
charge. Remove the four mounting screws, rotate the as-
sembly (including the gasket), then reinstall the mounting
screws. See figure 14. Use the provided wire tie to bundle
the pressure switch wires with the inducer motor power
leads. Route the power leads away from any moving
parts to prevent damage to the wires.
Combustion Air Inducer
90°
Flue Transition
(Do not remove
)
Mounting Screws
(Remove)

FIGURE 14

Optional Flue Outlet
Top Cap
Flue Outlet Hole
(Reattach
Cutout Here)
Cut out
FIGURE 15
90°
MOUNTING SCREWS
(Remove)
Power Leads
Supply Air
Opening
(Top View)
Optional Flue Outlet
(Side View)