Lennox G24M SERIES Guide

Page 1
WHAT TO DO IF YOU SMELL GAS:
If the information in this manual is not
followe exactly, a fire or explosion
may result causing property amage,
personal injury or loss of life.
WARNING
Do not store or use gasoline or other
flammable vapors an liqui s in the
vicinity of this or any other appliance.
Installation an service must be perĆ
forme by a qualifie installer, serĆ
vice agency or the gas supplier.
Do not try to light any appliance.
Do not touch any electrical switch; o not
use any phone in your buil ing.
Imme iately call your gas supplier from a
neighbor's phone. Follow the gas supplier's
instructions.
If you cannot reach your gas supplier, call
the fire epartment.
Extinguish any open flames.
RETAIN THESE INSTRUCTIONS
FOR FUTURE REFERENCE
G24M
SERIES
GAS FURNACE
503,746M
7/99
Supersedes 9/98
Litho USA

PRODUCT LITERATURE
1999 Lennox Industries Inc.
Dallas, Texas

Page 2
G24M PARTS IDENTIFICATION
UPFLOW POSITION DOWNFLOW POSITION
1
2
4
5
6
8
7
1
2
4
5
6
9
7
1 - COMBUSTION AIR
BLOWER
2 - PRESSURE SWITCH
3 - PRIMARY LIMIT
4 - GAS VALVE
5 - ROLLOUT SWITCH
(One on each si e)
6 - BURNERS
7 - BLOWER
8 - TRANSFORMER &
CIRCUIT BREAKER
9 - CONTROL BOARD
10 - SECONDARY LIMITS (2)
(Blower back)
8
9
10
3
3
10
WARNING
Pro uct contains fiberglass wool.Disturbing the
insulation in this pro uct uring installation,
maintenance, or repair will expose you to fiberĆ
glass wool. Breathing this may cause lung canĆ
cer. (Fiberglass wool is known to the State of
California to cause cancer.)Fiberglass wool may
also cause respiratory, skin, an eye irritation.To
re uce exposure to this substance or for further
information, consult material safety ata sheets
available from a ress shown below, or contact
your supervisor.
Lennox In ustries Inc.
P.O. Box 799900
Dallas, TX 75379-9900
WARNING
If overheating occurs or if gas supply fails to shut
off, shut off the manual gas valve to the appliance
before shutting off electrical supply.
WARNING
Do not use this furnace if any part has been un erĆ
water. Imme iately call a qualifie service techniĆ
cian to inspect the furnace an to replace any part
of the control system an any gas control which
has been un er water.
CAUTION
Before attempting to perform any service or mainteĆ
nance, turn the electrical power to unit OFF at isconĆ
nect switch.
IMPORTANT
Any a itions, changes, or conversions require in
or er for the appliance to satisfactorily meet the apĆ
plication nee s must be ma e by a Lennox service
technician using factory specifie an approve
parts.

Page 3
Important Directions
1 - Keep the furn ce re cle r nd free of combustible
m teri l, g soline, nd other fl mm ble v pors nd liqĆ
uids. If inst lled in n insul ted re , furn ce must be
kept free of insul ting m teri l. Insul ting m teri l m y
be combustible. Inspect furn ce venting system to
m ke sure it is in pl ce, physic lly sound, nd without
holes, corrosion, or block ge. Inspect furn ce return
ir duct connection to ensure duct is se led to the furĆ
n ce nd termin tes outside the sp ce cont ining the
furn ce. Inspect the physic l support of the furn ce to
gu r ntee th t it is sound without s gging, cr cks or
g ps round b se nd it m int ins se l between b se
nd support.
2 - DO NOT obstruct ir flow to unit. Unit must receive n
unobstructed flow of combustion nd ventil ting ir.
3 - DO NOT store chlorine or fluorine products ne r unit or
introduce these products into the combustion ir.
These products c n c use furn ce corrosion.
4- DO NOT raw return air from a room where this
furnace, or any other gas appliance (ie., a water
heater), is installe . When return ir is dr wn from
room, neg tive pressure is cre ted in the room. If
g s ppli nce is oper ting in room with neg tive
pressure, the flue products c n be pulled b ck down
the vent pipe nd into the room. This reverse flow of
the flue g s m y result in incomplete combustion nd
the form tion of c rbon monoxide g s. This toxic g s
might then be distributed throughout the house by
the furn ce duct system.
Your furnace is a gas appliance. It is critic l th t the g s
supplied to the unit be completely burned to void the proĆ
duction of c rbon monoxide g s. Complete combustion
of the g s requires, but is not limited to, correct g s presĆ
sure nd g s flow r te, dequ te combustion ir, nd
proper venting.
WARNING
Carbon monoxi e gas is invisible, o orless, an
toxic.
Exposure to this g s c n c use person l injury nd
even de th to ll occup nts, including pets. Any item
th t is powered by or gives off he t from combustion
process (including l wn mowers, utomobiles, nd fireĆ
pl ces) h s the potenti l to produce c rbon monoxide
g s. Bec use of this, Lennox recommen s the use of
a carbon monoxi e etector in your home, even if
you o not own gas appliances. Reli ble detectors
re v il ble t re son ble ret il prices. Cont ct your
independent Lennox de ler for more det ils bout this
investment in your s fety.
Your furn ce is designed to meet st nd rds set by n tionĆ
l gencies, nd to oper te s fely when properly inst lled
nd m int ined. However, the unit's perform nce c n be
gre tly imp cted by the individu l inst ll tion nd the opĆ
er ting environment. It is your responsibility to ensure
th t this ppli nce is m int ined. Proper m inten nce is
critic l for your s fety nd the s tisf ctory oper tion of the
product. Lennox strongly recommen s annual inĆ
spection an maintenance of this appliance. Cont ct
your independent Lennox de ler for n inspection by
qu lified service technici n.
Lighting Information an Operation
WARNING
If you o not follow these instructions exactly, a fire
or explosion may result causing property amage,
personal injury or loss of life.
BEFORE LI HTIN smell all around the appliance
area for gas. Be sure to smell next to the floor because
some gas is heavier than air and will settle on the
floor.
Use only your hand to push in or turn the gas control
knob. Never use tools. If the knob will not push in or turn
by hand, do not try to repair it, call a qualified service
technician. Force or attempted repair may result in a fire
or explosion.
To place G24M furnace into operation:
24M units are equipped with an electronic ignition
system. Do not attempt to manually light burners on
these furnaces. Each time thermostat calls for heat, the
burner will automatically light.
Gas Valve Operation (Figures 2 an 3)
1 - STOP! Re d the s fety inform tion t the beginning
of this section.
2 - Set thermost t to lowest setting. See figure 1.
THERMOSTATS
FIGURE 1
3 - Turn off ll electric l power to ppli nce.
4 - This ppli nce Is equipped with n ignition device
which utom tic lly lights the burner. Do not try to
light the burner by h nd.
5 - Remove the ccess p nel.

Page 4
6 - White Rodgers 36E Gas Valve - Switch g s v lve lever
to OFF. See figure 2.
Honeywell VR8205 Gas Valve - Turn knob on g s v lve
clockwise to OFF. Do not force. See figure 3.
WHITE RODGERS 36E SERIES GAS VALVE
GAS VALVE SHOWN IN OFF POSITION
FIGURE 2
ON
OFF
HONEYWELL VR8205 SERIES GAS VALVE
GAS VALVE SHOWN IN OFF POSITION
FIGURE 3
7 - W it five (5) minutes to cle r out ny g s. If you then
smell g s, STOP! Immedi tely c ll your g s supplier
from neighbor's phone. Follow the g s supplier's
instructions. If you do not smell g s go to next step.
8 - White Rodgers 36E Gas Valve - Switch g s v lve lever
to ON.
Honeywell VR8205 Gas Valve - Turn knob on g s
v lve counterclockwise to ON. Do not force.
9 - Repl ce the ccess p nel.
10 - Turn on ll electric l power to unit.
11 - Set thermost t to desired setting.
NOTE – When unit is initially started, steps 1 through 11
may need to be repeated to purge air from gas line.
12 - If the ppli nce still will not oper te, follow the
instructions To Turn Off G s To Unit" nd c ll your
service technici n or g s supplier.
To Turn Off Gas To Unit
1 - Set thermost t to lowest setting.
2 - Turn off ll electric l power to unit if service is to be
performed.
3 - Remove the ccess p nel.
4 - Switch lever on White Rodgers g s v lve to OFF; turn
knob on Honeywell v lve clockwise to OFF. Do not
force.
5 - Repl ce the ccess p nel.
Filters
24M series units are equipped with external filters
which should be inspected monthly and replaced
when necessary to assure proper furnace operation.
See table 1 for filter sizes. Replacement filters used
with 24M-40/60/75 units must have a minimum veĆ
locity rating of 400 FPM. Replacement filters used
with 24M-100/120/140 units require a minimum veĆ
locity rating of 625 FPM. Figures 4, 5, and 6 show posĆ
sible filter locations.
TABLE 1
FILTER SIZE
MODEL NUMBER UPFLOW DOWNFLOW
1 FILTER 2 FILTERS
G24M-45/60/75 16 in. X 20 in. X 1 in. 16 in. X 20 in. X 1 in.
G24M-100/120/140 20 in. X 20 in. X 1 in. 16 in. X 20 in. X 1 in.
UPFLOW FURNACE
BOTTOM RETURN AIR
FIGURE 4

Page 5
UPFLOW FURNACE
SIDE RETURN AIR
FIGURE 5
DOWNFLOW FURNACE
FILTERS IN PLENUM RACK
FIGURE 6
Blower
Check and clean blower wheel for any debris. Blower
motor is prelubricated for extended bearing life. No
further lubrication is needed.
WARNING
Blower oor must be securely in place when blower
an burners are operating. Gas fumes, which coul
contain carbon monoxi e, can be rawn into living
space resulting in personal injury or eath.
Burner Flame
The 24M burner flame is not adjustable; however,
the flame should be inspected at the beginning of
each heating season and burners should be cleaned,
if necessary. Burner flame should be blue when burnĆ
ing natural gas, blue/yellow when burning propane
gas.
BURNER FLAME
BURNER
FLAME
HEAT
EXCHANGER
TUBE
VEST
PANEL
FLAME APPEARS BLUE IF
BURNING NAT. GAS; BLUE/
YELLOW FOR PROPANE.
FIGURE 7
Venting System Inspection
Annually (before heating season) inspect furnace
venting system, vent cap, heat exchanger and burnĆ
ers for corrosion, deterioration, or deposits of debris.
Remove any obstructions.
Contact your Lennox dealer for a periodic unit inspecĆ
tion by a qualified service technician.
Flame Rollout Safety Switches
Your Lennox furnace is equipped with two flame roll-
out safety switches which shut off the gas supply to
the furnace in case of heat exchanger blockage. If the
furnace fails to operate due to the functioning of these
safety switches, DO NOT attempt to place the furnace
into operation. Contact a qualified service technician.
Service Remin er
Call your Lennox service technician if unit is inoperaĆ
tive. Before calling, always check the following to be
sure service is required.
1 - Check th t electric l disconnect switches re ON.
2 - Are ccess p nels securely in pl ce?
3 - Check room thermost t for proper setting.
4 - Repl ce ny blown fuses or reset circuit bre kers.
5 - G s v lve should be ON.
6 - Air filter should not be plugged limiting ir flow.
7 - Is g s turned on t meter?
8 - Is m nu l m in shutĆoff v lve open?
To keep your Lennox gas heating system in peak operatĆ
ing condition year after year, contact your independent
Lennox dealer about a planned service program.

Page 6
Safety Precautions
If you iscover any of the following, shut own your
unit, an contact an in epen ent Lennox ealer for
an inspection by a qualifie technician.
SIf you repe tedly he r ny new or unf mili r sounds
while your unit is oper ting, there m y be problem.
For ex mple, poorly performing burners c n produce
unf mili r noises.
SIf you smell ny unusu l odors, your unit m y be operĆ
ting improperly. For ex mple, units c n give off unf Ć
mili r odors if components re required to oper te in
bnorm l conditions.
SLook for visible signs of m lfunctioning unit. Ex mĆ
ples include unusu l mounts of condens te on winĆ
dows inside your house, visibly burnt components or
unusu l dirt or rust ccumul tions on the vent pipe or
in the unit.
SIf you experience he d che, n use , f tigue, or dizziĆ
ness, the c use could be exposure to c rbon monoxĆ
ide g s. This is often misdi gnosed s the flu bec use
symptoms re simil r. If you suffer from flu-like sympĆ
toms th t re ex gger ted t home, but seem to subĆ
side while you re w y from the house, exposure to
c rbon monoxide could be the c use.
Your vigil nce m y p y off in e rly detection of problem
before either person l injury or property d m ge occurs.
Do not hesit te to cont ct qu lified service technici n s
n investment in your well being.
Planne Service
You should expect service technici n to check the folĆ
lowing items during n nnu l inspection. Power to the
unit must be shut off for the service technici n's s fety.
Fresh air grilles an louvers (on the unit nd in the room
where the furn ce is inst lled) - Must be open nd unobĆ
structed to provide combustion ir.
Burners- Must be inspected for rust, dirt, or signs of w Ć
ter.
Vent pipe - Must be inspected for signs of w ter, d mĆ
ged or s gging pipe, or disconnected joints.
Unit appearance - Must be inspected for rust, dirt, signs
of w ter, burnt or d m ged wires, or components.
Fan access oor - Must be properly in pl ce nd provide
se l between the return ir nd the room where the furĆ
n ce is inst lled.
Return air uct - Must be properly tt ched nd provide
n ir se l to unit.
Operating performance - Unit must be observed during
oper tion to monitor proper perform nce of the unit nd
the vent system.
Combustion gases - Flue products must be n lyzed
nd comp red to the unit specific tions.
Problems detected during the inspection m y m ke it
necess ry to tempor rily shut down the furn ce until the
items c n be rep ired or repl ced.
Pay attention to your furnace. Situ tions c n rise beĆ
tween nnu l furn ce inspections th t m y result in unĆ
s fe oper tion. For inst nce, items innocently stored next
to the furn ce m y obstruct the combustion ir supply.
This could c use incomplete combustion nd the producĆ
tion of c rbon monoxide g s.