Lennox G27M 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
G27M
SERIES
GAS FURNACE
503,589M
7/99
Supersedes 9/98
Litho USA

PRODUCT LITERATURE
1999 Lennox Industries Inc.
Dallas, Texas

Page 2
G27M PARTS IDENTIFICATION
UPFLOW POSITION DOWNFLOW POSITION
1
2
3
4
5
7
8
1
2
3
4
5
7
8
1 - COMBUSTION AIR
BLOWER
2 - PRESSURE SWITCHES
3 - GAS VALVE
4 - ROLLOUT SWITCH
(One on each si e)
5 - BURNERS
6 - TWO-STAGE CONTROL
BOARD
7 - IGNITION CONTROL BOARD
8 - BLOWER
6
6
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 furnace area c ear and free of combustib e
materia , gaso ine, and other f ammab e vapors and iqĆ
uids. If insta ed in an insu ated area, furnace must be
kept free of insu ating materia . Insu ating materia may
be combustib e. Inspect furnace venting system to
make sure it is in p ace, physica y sound, and without
ho es, corrosion, or b ockage. Inspect furnace return
air duct connection to ensure duct is sea ed to the furĆ
nace and terminates outside the space containing the
furnace. Inspect the physica support of the furnace to
guarantee that it is sound without sagging, cracks or
gaps around base and it maintains sea between base
and support.
2 - DO NOT obstruct air f ow to unit. Unit must receive an
unobstructed f ow of combustion and venti ating air.
3 - DO NOT store ch orine or f uorine products near unit or
introduce these products into the combustion air.
These products can cause furnace 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 air is drawn from a
room, a negative pressure is created in the room. If a
gas app iance is operating in a room with negative
pressure, the f ue products can be pu ed back down
the vent pipe and into the room. This reverse f ow of
the f ue gas may resu t in incomp ete combustion and
the formation of carbon monoxide gas. This toxic gas
might then be distributed throughout the house by
the furnace duct system.
Your furnace is a gas appliance. It is critica that the gas
supp ied to the unit be comp ete y burned to avoid the proĆ
duction of carbon monoxide gas. Comp ete combustion
of the gas requires, but is not imited to, correct gas presĆ
sure and gas f ow rate, adequate combustion air, and
proper venting.
WARNING
Carbon monoxi e gas is invisible, o orless, an
toxic.
Exposure to this gas can cause persona injury and even
death to a occupants, inc uding pets. Any item that is powĆ
ered by or gives off heat from a combustion process (inĆ
c uding awn mowers, automobi es, and firep aces) has the
potentia to produce carbon monoxide gas. Because of
this, Lennox recommen s the use of a carbon monoxĆ
i e etector in your home, even if you o not own gas
appliances. Re iab e detectors are avai ab e at reasonĆ
ab e retai prices. Contact your independent Lennox dea er
for more detai s about this investment in your safety.
Your furnace is designed to meet standards set by nationĆ
a agencies, and to operate safe y when proper y insta ed
and maintained. However, the unit's performance can be
great y impacted by the individua insta ation and the opĆ
erating environment. It is your responsibi ity to ensure
that this app iance is maintained. Proper maintenance is
critica for your safety and the satisfactory operation of the
product. Lennox strongly recommen s annual inĆ
spection an maintenance of this appliance. Contact
your independent Lennox dea er for an inspection by a
qua ified service technician.
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 OPERATING sme a around the app iance
area for gas. Be sure to sme next to the f oor because
some gas is heavier than air and wi sett e on the f oor.
Use on y your hand to turn the gas contro knob. Never use
too s. If the knob wi not turn by hand, do not try to repair it,
ca a qua ified service technician. Force or attempted repair
may resu t in a fire or exp osion.
Placing Furnace Into Operation
G27M furnaces are equipped with an e ectronic ignition
system. Do not attempt to manua y ight burners on these
furnaces. Each time the thermostat ca s for heat, the
burners wi automatica y ight.
Gas Valve Operation (Figure 2)
1 - STOP! Read the safety information at the beginning
of this section.
2 - Set the thermostat to the owest setting. See figure 1.
THERMOSTATS
FIGURE 1
3 - Turn off a e ectrica power to the unit.
4 - This furnace is equipped with an ignition device
which automatica y ights the burners. Do not try to
ight the burners by hand.
5 - Remove the access pane .

Page 4
6 - White Rodgers 36E Gas Valve - Turn knob on gas
va ve 180° either way to OFF. See figure 1.
7 - Wait five minutes to c ear out any gas. If you then sme
gas, STOP! Immediate y ca your gas supp ier from a
neighbor's phone. Fo ow the gas supp ier's instructions.
If you do not sme gas go to next step.
WHITE RODGERS 36E SERIES GAS VALVE
GAS VALVE SHOWN IN OFF POSITION
pM
C
HI
FIGURE 2
8 - White Rodgers 36E Gas Valve - Turn knob on gas
va ve 180° either way to ON.
9 - Rep ace the access pane .
10 - Turn on a e ectrica power to to the unit.
11 - Set the thermostat 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 app iance wi not operate, fo ow the instrucĆ
tions Turning Off Gas to Unit" and ca your service
technician or gas supp ier.
Turning Off Gas to Unit
1 - Set the thermostat to the owest setting.
2 - Turn off a e ectrica power to the unit if service is to
be performed.
3 - Remove the access pane .
4 - White Rodgers 36E Gas Valve - Turn knob on gas
va ve 180° either way to ON.
5 - Rep ace access pane .
Two–Stage Operation
The G27M is a two-stage gas-fired furnace, which can be
contro ed by either a two-stage or sing e-stage room
thermostat.
The two-stage thermostat monitors the room temperature
and sends a signa to the G27M furnace when the temperĆ
ature fa s be ow the desired setpoint. The furnace is then
turned on at ow fire (first stage). If the room temperatures
continues to fa , the thermostat sends a signa to turn on
the unit at high fire (second stage).
When a sing e-stage thermostat is being used to contro
the operation of the G27M furnace, the unit can either opĆ
erate on high fire (second stage) at a times or the unit can
be made to start on ow fire (first stage) and automatica y
switch to high fire (second stage) after a time de ay, if the
demand is not satisfied on ow fire (first stage).
NOTE – For more details on available options and for unit
adjustment, contact the Lennox Technical Support De-
partment.
Filters
G27M series units are equipped with externa fi ters
which shou d be inspected month y and rep aced when
necessary to assure proper furnace operation. See
tab e 1 for fi ter sizes. Rep acement fi ters used with
G27M-60/75 units must have a minimum ve ocity ratĆ
ing of 400 FPM. Rep acement fi ters used with
G27M-100/120 units require a minimum ve ocity rating
of 625 FPM. Figures 3, 4, and 5 show possib e fi ter
ocations.
TABLE 1
FILTER SIZE
MODEL NUMBER UPFLOW DOWNFLOW
1 FILTER 2 FILTERS
G27M-45/60/75 16 in. X 20 in. X 1 in. 16 in. X 20 in. X 1 in.
G27M-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 3

Page
UPFLOW FURNACE SIDE RETURN AIR
FIGURE 4
DOWNFLOW FURNACE
FILTERS IN PLENUM RACK
FIGURE 5
Blower
Check and c ean b ower whee for any debris. B ower moĆ
tor is pre ubricated for extended bearing ife. No further uĆ
brication 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 G27M burner f ame is not adjustab e; however, the
f ame shou d be inspected at the beginning of each heatĆ
ing season and burners shou d be c eaned, if necessary.
Burner f ame shou d be b ue when burning natura gas.
BURNER FLAME
BURNER
FLAME
HEAT
EXCHANGER
TUBE
VEST
PANEL
FLAME APPEARS BLUE IF
BURNING NAT. GAS.
FIGURE 6
Venting System Inspection
Annua y (before heating season) inspect furnace venting
system, vent cap, heat exchanger and burners for corroĆ
sion, deterioration, or deposits of debris. Remove any obĆ
structions.
Contact your Lennox dea er for a periodic unit inspection
by a qua ified service technician.
Flame Rollout Safety Switches
Your Lennox furnace is equipped with two f ame ro -out
safety switches which shut off the gas supp y to the furĆ
nace in case of heat exchanger b ockage. If the furnace
fai s to operate due to the functioning of these safety
switches, DO NOT attempt to p ace the furnace into opĆ
eration. Contact a qua ified service technician.
Service Remin er
Ca your Lennox service technician if unit is inoperative.
Before ca ing, a ways check the fo owing to be sure serĆ
vice is required.
1 - Check that e ectrica disconnect switches are ON.
2 - Are access pane s secure y in p ace?
3 - Check room thermostat for proper setting.
4 - Rep ace any b own fuses or reset circuit breakers.
5 - Gas va ve shou d be ON.
6 - Air fi ter shou d not be p ugged imiting air f ow.
7 - Is gas turned on at meter?
8 - Is manua main shutĆoff va ve open?
To keep your Lennox gas heating system in peak opĆ
erating condition year after year, contact your indeĆ
pendent Lennox dealer about a planned service proĆ
gram.

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 repeated y hear any new or unfami iar sounds
whi e your unit is operating, there may be a prob em.
For examp e, poor y performing burners can produce
unfami iar noises.
SIf you sme any unusua odors, your unit may be operĆ
ating improper y. For examp e, units can give off unfaĆ
mi iar odors if components are required to operate in
abnorma conditions.
SLook for visib e signs of a ma functioning unit. ExamĆ
p es inc ude unusua amounts of condensate on winĆ
dows inside your house, visib y burnt components or
unusua dirt or rust accumu ations on the vent pipe or
in the unit.
SIf you experience headache, nausea, fatigue, or dizziĆ
ness, the cause cou d be exposure to carbon monoxĆ
ide gas. This is often misdiagnosed as the f u because
symptoms are simi ar. If you suffer from f u- ike sympĆ
toms that are exaggerated at home, but seem to subĆ
side whi e you are away from the house, exposure to
carbon monoxide cou d be the cause.
Your vigi ance may pay off in ear y detection of a prob em
before either persona injury or property damage occurs.
Do not hesitate to contact a qua ified service technician as
an investment in your we being.
Planne Service
You shou d expect a service technician to check the fo Ć
owing items during an annua inspection. Power to the
unit must be shut off for the service technician's safety.
Fresh air grilles an louvers (on the unit and in the room
where the furnace is insta ed) - Must be open and unobĆ
structed to provide combustion air.
Burners- Must be inspected for rust, dirt, or signs of waĆ
ter.
Vent pipe - Must be inspected for signs of water, damĆ
aged or sagging pipe, or disconnected joints.
Unit appearance - Must be inspected for rust, dirt, signs
of water, burnt or damaged wires, or components.
Fan access oor - Must be proper y in p ace and provide
a sea between the return air and the room where the furĆ
nace is insta ed.
Return air uct - Must be proper y attached and provide
an air sea to unit.
Operating performance - Unit must be observed during
operation to monitor proper performance of the unit and
the vent system.
Combustion gases - F ue products must be ana yzed
and compared to the unit specifications.
Prob ems detected during the inspection may make it
necessary to temporari y shut down the furnace unti the
items can be repaired or rep aced.
Pay attention to your furnace. Situations can arise beĆ
tween annua furnace inspections that may resu t in unĆ
safe operation. For instance, items innocent y stored next
to the furnace may obstruct the combustion air supp y.
This cou d cause incomp ete combustion and the producĆ
tion of carbon monoxide gas.