Combustion Air Inducer; Ignitor Location; Optional Flue Outlet - Lennox G40UH(X) Unit Information

Ignitor Location

IGNITOR TYPE
Silicon nitride
Mini Nitride
B"
BURNERS FRONT VIEW
FIGURE 11
7.Combustion Air Inducer (B6)
All G40UH(X) units use a combustion air inducer to move
air through the burners and heat exchanger during heating
operation. The blower uses a 120VAC motor. The motor
operates during all heating operation and is controlled by
furnace control A92. The inducer also operates for 15 sec-
onds before burner ignition (pre-purge) and for 5 seconds
after the gas valve closes (post-purge).
A proving switch connected to the combustion air inducer ori-
fice plate is used to prove inducer operation. The combustion
air inducer orifice will be different for each model. See table 8
for orifice sizes. The switch monitors air pressure in the induc-
er housing. During normal operation, the pressure in the
housing is negative. If pressure becomes less negative (sig-
nifying an obstruction) the proving switch opens. When the
proving switch opens, the furnace control (A92) immediately
closes the gas valve to prevent burner operation.
Horizontal Applications
The G40UH(X) furnace can be installed in horizontal ap-
plications.
The combustion air inducer may be rotated clockwise or
counterclockwise by 90° to allow for vertical vent discharge
in a horizontal application. Remove the four mounting
screws, rotate the assembly (assembly consists of orifice
plate, proving switch, gasket and combustion air inducer),
then reinstall the mounting screws. See figure 12. Use the
provided wire tie to bundle the pressure switch wires with
the inducer motor power leads. Route the wires away
from moving parts and the heat of the inducer motor to
prevent damage to the wires. Use sheet metal shears to
remove the cut out from the side of the cabinet. See figure
13. Use the two provided sheet metal screws to install the
cut out on the top cap to cover the original flue outlet open-
ing.
A" B"
.625 .406
.685 .306
MEASUREMENT IS TO I.D.
A"
OF RETENTION RING
BRACKET
G40UH−15 and later assembly shown

Combustion Air Inducer

90°
Flue Transition
(Do not remove
)
Mounting Screws
(Remove)
(Horizontal Installation)
Top Cap
Flue Outlet Hole
Reattach
(
Cutout Here)
G40UH(X) Unit
24A/36A−070
48B−070−1 to −10
48B−070−14 and later
36C−110 (−1, −2, −3 units)
36C−110 (−6 and later)
−48C, 60C−110 (−1, −2, −3 units)
48C, 60C−110 (−4, −5 units)
48C, 60C−110 (−6 and later)
−135 (−1, −2, −3, −4, −5 units)
−135 (−6 and later units)
Page 21
(Upflow Position)
MOUNTING SCREWS
(Remove)
Power Leads
FIGURE 12

Optional Flue Outlet

Top View of Furnace
Supply Air
Opening
Cut out
Optional
Flue Outlet
FIGURE 13
TABLE 8
C.A.I. Orifice Size
−045
−090
−155
90°
1.250
1 .438
1.5
1.438
1.688
2.156
2.0
1.875
2.156
2.0
2.156
2.375
2.60