Lennox O24-105, O24-120, O24-140, O24-154, OF24-105 Information Manual

O24/OF24

Service Literature

Corp. 9804-L4

O24 / OF24 SERIES UNITS

O24 (Elite 80) series units are heating only mid-efficiency
upflow oil furnaces manufactured with Beckett oil burners.
O24 units are available in heating capacities of 70,000 to
154,000 Btuh (20.5 to 45.1 kW). O24 units are suitable for resi
dential or commercial applications.
OF24 (Elite 80) series units are heating only mid-efficiency lo­boy up-flow furnaces, which cime in front (OF24) or rear
(OF24R) flue openings. Both furnaces use Beckett oil burners
with heating capacities of 105,000 to 154,000 Btuh (30.8 kW to

45.1 kW). OF24 units are suitable for residential or commercial
application.

The drum type heat exchanger comes with strategically
placed ports allowing easy cleaning. The oil burner can be
easily removed for inspection and service. The mainte
nance section gives a detailed description on how this is
done.

Information contained in this manual is intended for use by
experienced HVAC service technicians only. All specifica
tions are subject to change. Procedures outlined in this
manual are presented as a recommendation only and do not
supersede or replace local or state codes.

OF24

REAR FLUE

MODEL

O24 UPFLOW

OF24

FRONT FLUE

MODEL

Page 1

 1998 Lennox Industries Inc.

Litho U.S.A.

SPECIFICATIONS O24

Model Number O24-70 O24-105/120 O24-140/154

Input - Btuh (kW) low/high 70,000 (20.5) 105,000 / 120,000(30.8 / 35.2) 140,000 / 154,000(41.0 / 45.1)

Output - Btuh (kW) low/high 57,000 (16.7) 85,000 / 97,000 (24.9 / 28.4) 113,000 / 125,000 (33.1 / 36.6)

A.F.U.E. 82% 81% 82%

Nozzle Rating - gph (L/hr) and spray angle .50 (1.9) - 80° hollow

Flue Size Diameter - in. (mm) 6 (152)

Temperature Rise - F (C) 55 - 85 (30 - 47)

Oil Burner pump 1 Stage

Oil Burner pump pressure - psig (Pa) 100 (690) 140 (965)

Oil Burner air inlet connection (dia.) - in. (mm) 4 (102)

Motor hp (W) 1/6 (124) 1/4 (187) 3/4 (560)

Motor pulley - in. (mm) 3-1/4 (83) 4 (102)

Blower

Number and size of filters - in. (mm) (1) 16 x 25 x 1 (2) 16 x 25 x 1

Shipping weight - lbs. (kg) 1 package 225 (102) 275 (125)

Electrical characteristics 115 volts - 60 hertz - 1 phase

Two Stage Oil Pump 65A44

Oil Filter - 10 micron, no mounting bracket 91P89

Oil Filter - 10 micron, with mounting bracket 53P92

Replacement cartridge for above - 10 micron, 45 gph (170 L/h) 53P93

Filter restriction indicator gauge 53P90

Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and FTC labeling regulations. Isolated combustion system rating for nonweatherized furnaces.
Nozzle must be field provided for field conversion to higher heating input.
Cleanable frame type filters. Furnished with unit in Side Filter Adaptor Kit for field installation external to the cabinet.

Requires return air from both sides of cabinet.

Blower wheel nominal diameter x width - in. (mm) 10 x 8 (254 x 203) 12 x 9 (305 x 229)

Blower pulley - in. (mm) 7 (178)

Data

Belt size - in. (mm) 40 (1016) 41 (1041)

cfm (L/s) at .20 in. wg. (50 Pa) external static
pressure

 Optional Accessories (Must Be Ordered Extra) 

820 (390) 1170 (550) 1550 (730)

.65 (2.5) - 80°(-105 input) solid

.75 (2.8) - 80° (-120 input) solid

55 - 85 (30 - 47)(-105)
60 - 90 (33 - 50)(-120)

.85 (3.2) - 80° (-140 input) solid

1.00 (3.8) - 80° (-154 input) solid

50 - 80 (28 - 45)(-140)

60 - 90 (33 - 50)(-154)

Page 2

SPECIFICATIONS OF24(R)

Blower

Model Number

Input - Btuh (kW) low/high 105,000 / 120,000 (30.8 / 35.2) 140,000 / 154,000 (41.0 / 45.1)

Output - Btuh (kW) low/high 85,000 / 97,000 (24.9 / 28.4) 113,000 / 125,000 (33.1 / 36.6)

A.F.U.E. (low/high) 81%

Nozzle Rating - gph (L/hr) and spray angle

Flue Size Diameter - in. (mm) 6 (152)

Temperature Rise - F (C)

Oil Burner Pump 1 Stage

Oil Burner Pump Pressure - psig (Pa) 140 (965)

Oil Burner air inlet connection (dia.) - in. (mm) 4 (102)

Motor hp (W) 1/4 (187) 3/4 (560)

Motor pulley - in. (mm) 4 (102)

Blower wheel nominal diameter

Blower

Data

Number and size of filters in. (mm)

Shipping weight- - lbs. (kg) 1 package 255 (116) 290 (132)

Electrical Characteristics 115 volts - 60 hertz - 1 phase

Two Stage Oil Pump 65A44

Oil Filter - 10 micron, no mounting bracket 91P89

Oil Filter - 10 micron, with mounting bracket 53P92

Replacement cartridge for above - 10 micron, 45 gph (170 L/h) 53P93

Filter restriction indicator gauge 53P90

Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces.

Nozzle must be field provided for field conversion to higher heating input.

x width - in. (mm)

Blower pulley - in. (mm) 7 (178)

Belt size - in. (mm) 41 (1041) 42 (1067)

cfm (L/s) at .20 in. wg. (50 Pa) external static
pressure

 Optional Accessories (Must Be Ordered Extra) 

OF24-105/120

OF24-105/120R

.65 (2.5) - 80° (-105 input)

.75 (2.8) - 80° (-120 input)

45 - 75 (25 - 42) (-105 input)
55 - 85 (31 - 47) (-120 input)

10 x 8 (254 x 203) 12 x 9 (305 x 229)

1300 (615) (-105 input)
1220 (575) (-120 input)

(1) 18 x 19 x 1

(457 x 483 x 25)

OF24-140/154

OF24-140/154R

.85 (3.2) - 80° (-140 input)

1.00 (3.8) - 80° (-154 input)

50 - 80 (28 - 45) (-140 input)

55-85 (31 - 47) (-154 input)

1750 (825) (-140 input)
1700 (800) (-154 input)

(1) 19 x 21 x 1

( 483 x 533 x 25)

Page 3

CLEAN-OUT PORT

LIMIT SWITCH

BECKETT

AFII BURNER

COMBUSTION AIR INTAKE

INDOOR BLOWER

O24 GENERAL PARTS ORIENTATION

HEAT EXCHANGER

FLUE OPENING

CLEAN-OUT PORT

OBSERVATION PORT

BLOWER MOTOR

FLUE OPENING

CLEAN-OUT PORT

FAN LIMIT SWITCH

OBSERVATION PORT

FIGURE 1

OF24 GENERAL PARTS ORIENTA

TION

FILTER

INDOOR BLOWER

HEAT EXCHANGER

BECKETT

AFII BURNER

CLEAN-OUT PORT

FIGURE 2

Page 4

Unit

Lennox Burner

Part Number

TABLE 1

FURNACE / BURNER SPECIFICATIONS

Burner

Model

*Initial Air

Dial

Setting

Output

Nozzle Size

(Delevan)

Pump

Pressure

Head

70 35K74 AFII 85 3.0

105 35K75 AFII 85 4.0

120 35K75 AFII 85 4.5

140 35K76 AFII 150 6.0

154 35K76 AFII 150 6.5

*NOTE: The initial air dial setting is provided to get unit started. The air dial setting MUST be adjusted after startup to
achieve proper combustion.

ELECTROSTATIC DISCHARGE (ESD)

Precautions and Procedures

CAUTION

Electrostatic discharge can affect electronic
components. Take precautions during furnace
installation and service to protect the furnace's
electronic controls. Precautions will help to avoid
control exposure to electrostatic discharge by
putting the furnace, the control and the techni
cian at the same electrostatic potential. Neutral
ize electrostatic charge by touching hand and all
tools on an unpainted unit surface, such as the
gas valve or blower deck, before performing any
service procedure.

57,000 BTU

(16.7 kW)

84,000 BTU

(24.6 kW)

105,000 BTU

(30.8 kW)

112,000 BTU

(32.8 kW)

125,000 BTU

(36.6 kW)

motor shaft also connects to the direct drive oil pump
through a coupler. The burner motor turns both the com
bustion air blower and the oil pump. The motor operates
at 3500 RPM.

Burner motors are overload protected. In the event of ex
cess motor temperature or current, the overload opens
to de-energize the motor. The overload automatically re
sets after temperature has returned to normal. Keep mo
tor clean to prevent starting switch from sticking. All AFII
motors are permanently lubricated. No further oiling is required.

0.50 X 80A

0.65 X 80B

0.75 X 80B

0.85 X 80B

1.00 X 80B

2-Combustion Air Blower / Pump Fuse (F22)

(-140 and -154 CSA units only)

In the -140 and -154 Canadian units an in line fuse (F22) is
used between the line voltage from the blower control and
the blower / pump motor. The fuse is rated at 300 volts and
15 amps.

100 psig

(689.5 kPa)

140 psig

965.3 kPa)

140 psig

965.3 kPa)

140 psig

965.3 kPa)

140 psig

965.3 kPa)

FB0

FB3

FB3

FB6

FB6

3- Pump

The O24 and OF24 oil furnaces use a single stage, 3450
RPM pump. A two stage pump is available as an option
(catalog # 65A44). The oil burner is shipped from factory

I-UNIT COMPONENTS

General parts orientation for the O24 and OF24 are shown in
figures 1 and 2 respectively. The O24 and OF24 burner, limit
switch and cleanout ports may be accessed by removing the
front access panel. The blower can be accessed in the O24
and OF24 by removing the blower access panel.

A-Burner (Figure 3)

The O24 and OF24 oil furnaces use the Beckett AFII burner.
The oil burner provides an atomized oil vapor mixed with the
correct proportion of air when it is ignited in the combustion
chamber. Oil burner minimum and maximum ratings are listed
on the unit nameplate. Proper air adjustment for these ratings
is achieved through the air adjustment dial. Set air dial to the
initial air dial setting (see table 1). After start up adjust air dial to
achieve proper combustion. Remember to tighten set screw on
air dial.
The AFII burner is available in five sizes with either a single

or two stage pump. Table 1 identifies the burners used in
Lennox units. Figure 3 shows the typical layout of the burner
assembly.

1-Combustion Air Blower / Pump Motor (B6)

The burner is activated by the primary control. A com
bustion air blower is mounted on the motor shaft. The

for use in a single line system. To convert the pump to a
two line system, install the bypass plug provided in the at
tached bag according to the accompanying instructions.

4-Burner Control (A3) & Transformer (T1)

The burner control, along with the matching cad cell, proves
flame and controls the burner. After the cad cell closes a circuit
to the burner control, the burner control de-energizes the safety
switch heater to allow the unit to operate normally. The burner
control allows 45 seconds for the cad cell to close. If the cad cell
remains open after the 45 second time frame, the burner con
trol locks out. The burner control must be manually reset by de
pressing the red reset button on top of the burner control.
Transformer (T1) is part of the burner control. T1 provides

24VAC to the low voltage components in the unit and to the
thermostat.

5-Cad Cell (R26)

Together the cad cell and the burner control prove flame.
The cad cell senses the presence of burner light (less re
sistance) to close a circuit to the burner control.

IMPORTANT-Burner should not be installed so it is ex
posed to direct sunlight or electric bulb light. If the cell
is exposed to light on start up, the burner will not oper
ate.

Page 5

RETAINING

CLIP

HEAD

INSULATOR

O24 / OF24 OIL BURNER PARTS ARRANGEMENT

AIR TUBE
SCREWS

HOLE PLUG

CONNECTOR

AIR TUBE

ASSY FOR

FB HEADS

FB-HEAD

NOZZLE

ADAPTER

NOZZLE LINE

ELECTRODE HEAD

FLANGE

GASKET

ASSY.

FLANGE

ELECTRODE

ASSY

ELECTRONIC IGNITION

TRANSFORMER

MAIN

HOUSING

ASSY

ESCUTCHEON

PLATE

TUBE

REAR ACCESS

DOOR GASKET

VIEW PORT

REAR ACCESS

DOOR ASSY

SPLINED

OIL PUMP

ELECTRONIC IGNITION

TRANSFORMER

NUT

BURNER

CONTROL

RESET

BUTTON

AIR

ADJUSTMENT DIAL

0

3

4

5
6

7
8

COUPLING

COMBUSTION AIR

MOTOR

BLOWER

FIGURE 3

Page 6

WHEEL

INLET

AIR SCOOP

6-Electronic Ignitor (A73)

The electronic ignitor provides the needed hot spark at the
electrodes to ignite the fuel mixture. The ignitor is a solid state
transformer which has 115V primary and 14,000V secondary
windings. The center of the secondary winding is grounded.
Each secondary terminal is 7000V to ground and the total volt
age between the electrodes is 14,000V.

NOTE-The leads for the solid state transformer are re
placeable and are available in a kit form.

NOTE-When testing the solid state transformer, do not
use a transformer tester designed for iron magnet trans
formers. Damage to the tester may result.

7-Gun Assembly

The gun assembly receives oil from the oil pump and feeds
it to the nozzle. The nozzle converts liquid oil into a fog-like
mist that is discharged through the flame retention head
into the combustion chamber.

8-Flame Retention Heads

The stainless steel flame retention head (see figure 4) is
used to swirl (cone) the foglike oil and air mixture as it
enters the combustion chamber. Three different heads
are used in the O24/OF24. The firing rate dictates which
head is used. See table 1. The greater the FB number the
larger the slots on the head. When combustion takes
place, the flame will be cylindrical compact shaped as a
result.

B-Primary Fan/Limit Control (S10)

The primary limit on all O24and OF24 units, is located on
the vestibule panel (see figures 1 and 2 for location and fig
ure 5 for type). When excess heat is sensed in the heat ex
changer, the limit will open. If the limit is tripped, the blower
control deenergizes the thermostat, in turn shutting
down the un i t . The lim i t automatically resets when unit tem
p

erature returns to normal. See table 2 for limit set-points. The

fan control is factory set and is temperature acuated to con
trol blower operation. The fan control is set at 125F (52C )
on /100F (38C) off.

CAUTION

This furnace must not operate with a FAN ON

temperature greater than 130 degrees.

TABLE 2

PRIMARY LIMIT CONTROL (S10)

UNIT

O24-70 210F (99C) 180F (82C)

O24-105/120 220F (104C) 190F (88C)

O24-140/154 210F (99C) 180F (82C)

OF24-105/120

OF24-105/120R

OF24-140/154

OF24-140/154R

ACTUATES

ON TEMP. RISE

240F (116C) 210F (99C)

210F (99C) 180F (82C)

ACTUATES

ON TEMP. FALL

FLAME RETENTION HEAD

FB3 SHOWN

FIGURE 4

LIMIT CONTROL (S10)

S10

FIGURE 5

Page 7

TABLE 3

BLOWER MOTOR AND CAPACITOR RATINGS

Unit

O24-70 35K59

O24-105/120 35K59

O24-140/154 35K62

OF24-105/120
OF24-105/120R

OF24-140/154
OF24-140/154R

Blower Motor

Part Number

35K59

35K62

Power Volts Hz Phase

1/3 HP

(248.6 KW)

1/3 HP

(248.6 KW)

3/4 HP

(559.5 KW)

1/3 HP

(248.6 KW)

3/4 HP

(559.5 KW)

C-Blower Compartment

Blower motor (B3) and capacitor (C4), are located in the
blower compartment. The blower compartment can be ac
cessed by removing the blower access panel.

1-Blower Motor (B3) and Capacitor (C4)

All O24 and OF24 series units use single phase belt drive
blower motors. All motors used are 115V permanent split ca
pacitor motors to ensure maximum efficiency. See table 3
for horsepower and capacitor ratings.

D-Optional Accessories

Optional accessories are available from Lennox for the O24
and OF24 series units. Some accessories are in kit form which
come with instructions.

1- Continues Low Speed Blower On - Off
Switch (S68)

The low speed on  off switch is a kit (catalog # 67H91) which
permits continuous low speed blower operation. The switch is
a DPDT toggle switch.

2-Economizer Relay (K43)

The economizer relay (catalog # 65G40) is used to energize
the economizer if used. The relay is a 120V coil, single pole
contact.

Capacitor

Part Number

115 60 1 35K57 7.5 370

115 60 1 35K57 7.5 370

115 60 1 35K58 12.5 370

115 60 1 35K57 7.5 370

115 60 1 35K58 12.5 370

An oil filter is required for all models. Use an oil filter of gener
ous capacity for all installations. Install filter inside the building
between the tank shut-off valve and the burner. Locate filter
close to burner for easy servicing. The GAR-Ber 11BV-R or
equivalent filter (with the below specifications) is recom
mended.

Maximum Firing Rate: 10GPH (38LPH)

Micron Removal: 10

Filtering Area: 500 in.

Working Pressure: 15 PSI (103.4 kPa)

Inlet/Outlet Dimension: 3/8" (9.5 mm) NPT

Flow Rate: 45GPH (171LPH)

Care must be taken to ensure the restriction of the piping sys
tem, plus any lift involved, does not exceed the capabili
ty of the oil pump. Each installation will be different. Use
the following guide lines when determining to use a single or
two stage pump.

When using a single pipe system with the fuel supply level
with or above the burner (see figure 6) and a vacuum of 6" (152
mm) Hg or below, a single stage fuel unit with a supply line and
no return line should be adequate. Manual bleeding of the fuel
unit is required on initial start up. Failure to bleed air from the
pump could result in an air lock/oil starvation condition.

NOTE-As an extra precaution, cycle heating on and off
ten times after bleeding air from the pump. This will elimi
nate air in the gun assembly.

2

(3225.8 cm2)

MFD Volts

II-PLACEMENT AND INSTALLATION

Make sure unit is installed in accordance with installation in
structions and applicable codes.

A-Piping

The piping system and it's components (oil filter, safety valves,
shutoff valves, etc.) must be designed to provide clean, air free
fuel to the burner.

When using a two pipe system with the fuel supply level
below the level of the burner (see figure 7) a single stage
fuel unit should be used in lift conditions of up to 10 feet
(3 m) and/or a vacuum of 10" (254 mm) Hg or below. A
two stage fuel unit should be used when lift exceeds 10
feet (3 m) and/or a vacuum of 10" (254 mm) Hg to 15" (381
mm) Hg. Both conditions require the use of a return line that
purges the fuel unit of air by returning it to the fuel tank. Use
table 4 when determining the run and lift for piping.

Page 8

Before converting a onepipe system to a twopipe sys

g

tem the pump must be converted to a twopipe system.
To convert the pump, install the bypass plug according to
the instructions. Notice in the twopipe system the return
line must terminate 3" (76 mm) to 4" (102 mm) above the
supply inlet. Failure to do this may introduce air into the
system and could result in loss of prime.

NOTE-If using an outside tank in cold climates a number one
fuel or an oil treatment is strongly recommended.

Fill

Pipe

Air Vent

OIL PIPING

ONEPIPE SYSTEM

Fuel
Unit

Oil

Tank

Shut-off

Valve

Aux

Filter

8 ft (2.4 m)

Maximum

One Pipe Lift

FIGURE 6

OIL PIPING

TWOPIPE SYSTEM

Air Vent

Fill

Pipe

Return

Line

Oil

Tank

3"-4"

(76mm -102mm)

Return

Line

OUTSIDE TANK FUEL UNIT ABOVE BOTTOM OF TANK.

R

FIGURE 7

Fuel
Unit

Aux

Filter

Inlet

H

TABLE 4

TWO-PIPE MAXIMUM LINE LENGTH (H + R)

3450 RPM - 3 GPH (11.4 LPH)

Lift H"

Figure 6

0'

(0.0 m)

2'

(0.6 m)

4'

(1.2m)

6'

(1.8m)

8'

(2.4m)

10'

(3.0m)

12'

(3.7m)

14'

(4.3m)

16'

(4.9m)

18'

(5.5m)

3/8" (10 mm) OD

Tubing

Single

Stage

84'

(25.6 m)

73'

(22.3 m)

63'

(19.2 m)

52'

(15.8 m)

42'

(12.8 m)

31'

(9.4 m)

21'

(6.4 m)

---

---

Two

Stage

93'

(28.3 m)

85'

(25.9 m)

77'

(23.5 m)

69'

(21.0 m)

60'

(18.3 m)

52'

(15.9 m)

44'

(13.4 m)

36'

(11.0 m)

27'

(8.2 m)

--- --- ---

1/2" (12 mm) OD

Tubing

Single

Stage

100'

(30.5 m)

100'

(30.5 m)

100'

(30.5 m)

100'

(30.5 m)

100'

(30.5 m)

100'

(30.5 m)

83'

(25.3 m)

41'

(12.5 m)

---

Two

Stage

100'

(30.5 m)

100'

(30.5 m)

100'

(30.5 m)

100'

(30.5 m)

100'

(30.5 m)

100'

(30.5 m)

100'

(30.5 m)

100'

(30.5 m)

100'

(30.5 m)

(23.2 m)

B-Venting Considerations

WARNING

Combustion air openings in front of the furnace
must be kept free of obstructions. Any obstruction
will cause improper burner operation and may re
sult in a fire hazard or injury.

WARNING

The barometric shall be in the same atmospheric
pressure zone as the combustion air inlet to the
furnace. Deviation from this practice will cause im
proper burner operation and may result in a fire
hazard or injury.

76'

CAUTION

Do not store combustible materials near the fur
nace or supply air ducts. The material (such as
paint, motor oil, gasoline, paint thinner, etc.) may
ignite by spontaneous combustion creating a fire
hazard.

Page 9