Lennox LF24-100 User manual

506682−01
*P506682-01*
E2011 Lennox Industries Inc.
Dallas, Texas, USA
Litho U.S.A.
INSTALLATION
INSTRUCTIONS
LF24
100,000 to 400,000 Btuh Series
UNIT HEATERS
506682−01
5/2011
Supersedes 503,523M
Table Of Contents
LF24 Unit Dimensions 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Shipping 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Optional Accessories 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CSA Requirements in USA 3. . . . . . . . . . . . . . . . . . . . . . . . .
CSA Requirements in Canada 3. . . . . . . . . . . . . . . . . . . . . .
Additional Requirements 3. . . . . . . . . . . . . . . . . . . . . . . . . . .
Unit Heater Installation 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Combustion and Ventilation Air 4. . . . . . . . . . . . . . . . . . . . .
Rotation of Combustion Air Inducer 5. . . . . . . . . . . . . . . . . .
Venting 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Electrical Connections 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Typical LF24 Wiring Diagram 10. . . . . . . . . . . . . . . . . . . . . . .
Gas Connection 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Leak Check 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RETAIN THESE INSTRUCTIONS
FOR FUTURE REFERENCE
Unit Start−Up 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
To Turn Off Gas to Unit 13. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Heating Sequence of Operation 13. . . . . . . . . . . . . . . . . . . . .
Ignition Control LED 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
High Altitude Adjustment 13. . . . . . . . . . . . . . . . . . . . . . . . . . .
Gas Flow 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gas Pressure Adjustment 15. . . . . . . . . . . . . . . . . . . . . . . . . .
Limit Control Switch 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Louver Vane Adjustments 15. . . . . . . . . . . . . . . . . . . . . . . . . .
Combustion Air Pressure Switch 15. . . . . . . . . . . . . . . . . . . . .
Service 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Start−Up and Performance Checklist 16. . . . . . . . . . . . . . . . .
Template 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
WHAT TO DO IF YOU SMELL GAS:
Do not store or use gasoline or other
flammable vapors and liquids in the vi-
cinity of this or any other appliance.
Installation and service must be per-
formed by a qualified installer, service
agency or the gas supplier.
SDo not try to light any appliance.
SLeave the building immediately.
SDo not touch any electrical switch; do not use
any phone in your building.
SImmediately call your gas supplier from a
neighbor’s phone. Follow the gas supplier’s in-
structions.
SIf you cannot reach your gas supplier, call the
fire department.
FIRE OR EXPLOSION HAZARD.
Failure to follow safety warnings exact-
ly could result in serious injury, death,
or property damage.
WARNING
Be sure to read and understand the
installation, operation and service in-
structions in this manual.
Improper installation, adjustment, alter-
ation, service or maintenance can cause
serious injury, death or property damage.

Page 1
LF24 Unit Dimensions
1/2
(13)
TOP VIEW
SIDE VIEW
ADJUSTABLE
LOUVERS
GAS
VALVE
HEAT
EXCHANGER
DIRECT
DRIVE FAN
FLUE
OUTLET
ELECTRICAL INLETS
3/8" x 16 MOUNTING NUTS
FOR UNIT SUSPENSION
AIR
FLOW
COMBUSTION AIR
INDUCER
END VIEW
A
B
C
E
F
G
NOTE  LF24 models 100, 115, 145, 175 and
200 have a single fan. LF24 models 230, 250, 300,
345 and 400 have two fans.
D
*7-5/8
(194) 1/2
(13)
Additional
mounting nuts
furnished on
LF−230,
LF24−250,
LF24−300,
LF24−345 and
LF24−400 models
only.
H
NOTE  Two mounting nuts are furnished on
LF24 models 100, 115, 145, 175 and 200. Four
mounting nuts are furnished on LF24 models
230, 250, 300, 345 and 400 models.
Unit
A B C D E F G H
in. mm in. mm in. mm in. mm in. mm in. mm in. mm in. mm
LF24-100
LF24-115
LF24−145
31-5/16 795 32-3/16 817 20-3/16 512 11-1/2 292 19-1/16 484 11-3/4 298 3-1/4 83 7-7/8 200
LF24−175
LF24−200 31-5/16 795 32-3/16 817 23-1/8 588 11-1/2 292 22-1/16 560 8−1/2 216 3-1/4 83 8−11/16 220
LF24-230*
LF24−250*
LF24−300*
31-5/16 795 32-3/16 817 41-1/8 1045 3-11/16 97 40 1016 17-3/4 451 3-1/2 89 8-11/16 220
LF24-345*
LF24−400* 31-5/16 795 32-3/16 817 41-1/8 1045 3-11/16 97 40 1016 17-1/2 445 3-1/2 89 9-13/16 248
*Unit contains dual fans.
Shipping
The heater is completely assembled and is shipped with installation and operating instructions, warranty certificate and
flue transition. Check the unit for shipping damage. The receiving party should contact the last carrier immediately if any
shipping damage is found.

Page 2
Optional Accessories
TABLE 1
LF24−100 to LF24−230
Gas
Heating
Performance
Model No. − Stainless Steel LF24−100S LF24−115S LF24−145S LF24−175S LF24−200S
Model No. − Aluminized Steel LF24−100A LF24−115A LF24−145A LF24−175A LF24−200A
Optional Accessories − Must Be Ordered Extra
Discharge
Nozzle
30_− 94K94 SSS
30_− 94K95 S S
45_− 95K98 SSS
45_− 95K99 S S
60_− 16L28 SSS
60_− 16L29 S S
90_− 15L96 SSS
90_− 15L97 S S
Hanging Bracket
Kit 87277 SSSSS
High Altitude
Pressure Switch
Kit 10K73 S1S1S1S2− − −
LPG/Propane Kit
45L85 S
63J56 S S S
20L07 S
63J57
1LF24−100 through −145 require replacement combustion air inducer pressure switch at altitudes over 5500 feet above sea level.
2LF24−175 requires replacement combustion air inducer pressure switch at altitudes over 2500 feet above sea level.
TABLE 2
LF24−230 to LF24−400
Gas
Heating
Performance
Model No. − Stainless Steel LF24−230S LF24−250S LF24−300S LF24−345S LF24−400S
Model No. − Aluminized Steel LF24−230A LF24−250A LF24−300A LF24−345A LF24−400A
Optional Accessories − Must Be Ordered Extra
Discharge
Nozzle
30_− 94K96 SSSSS
45_− 95K00 SSSSS
60_− 16L30 SSSSS
90_− 15L98 SSSSS
Hanging Bracket
Kit 87277 SSSSS
LPG/Propane Kit
45L88 S S
63J57 S S
20L06 S

Page 3
CSA Requirements in USA
Installation of gas unit heaters must conform with local
building codes or, in the absence of local codes, with the
current edition of ANSI−Z223.1, National Fuel Gas Code.
Installation in aircraft hangers must be in accordance with
the current edition of ANSI/NFPA No. 409, Standard for
Aircraft Hangers.
Installation in parking structures must be in accordance
with the current edition of ANSI/NFPA No. 88A, Standard
for Parking Structures.
Installation in repair garages must be in accordance with
the current edition of ANSI/NFPA No. 88B, Standard for
Repair Garages.
Authorities having jurisdiction should be consulted before
installation. Air for combustion and ventilation must
conform to the methods outlined in the current edition of
ANSI Z223.1, Section 5.3, Air for Combustion and
Ventilation, or applicable provisions of local building
codes.
The National Fuel Gas Code (ANSI−Z223.1) is available
from:
American National Standard Institute Inc.
11 West 42nd Street
New York, NY 10036
These units are CSA international design−certified. These
unit heaters are certified for clearances to combustible
material as listed in table 1 and on unit rating plate.
Accessibility and service clearances must be observed in
addition to fire protection clearances.
All electrical wiring and grounding for unit must be in
accordance with the regulations of the current edition of
ANSI/NFPA No. 70, National Electric Code.
The National Electric Code is available from:
National Fire Protection Association
1 Batterymarch Park
PO Box 9101
Quincy, MA 02269−9101
CSA Requirements in Canada
These instructions are intended only as a general guide
and do not supersede local codes in any way. Authorities
having jurisdiction should be consulted before
installation. The installation must conform with local
building codes or, in the absence of local codes, with the
current edition of CSA−B149 installation compliance
codes. All electrical wiring and grounding for the unit must
also comply with the current edition of CSA C22.1,
Canadian Electrical Code.
These unit heaters are CSA−certified for clearances to
combustible material listed on the rating plate and table 3.
Adequate clearance must be provided around the
appliance and around air openings into the combustion
chamber. Provision must be made for service
accessibility.
NOTE: Fire protection clearances may be exceeded to
provide additional space for service and accessibility.
TABLE 3
UNIT CLEARANCES TO COMBUSTIBLE MATERIALS
Top Sides Bottom Rear Flue
in mm in mm in mm in mm in mm
6 152 6 152 0 0 18 457 6 152
GARAGE / WAREHOUSE INSTALLATIONS
1 − In a storage area, clearance from the heater to
combustible materials must be such that the
combustible material must not attain a temperature
above 160°F (71°C) during continuous operation of
the unit.
WARNING
Combustible materials that are affected by ex-
posure to temperatures less than 160°F (plas-
tics, plastic wrap, styrofoam, cardboard, etc.)
must be stored well away from this heater. Dis-
charge air temperatures for these units can ap-
proach 200°F.
2 − Maintain an 8−foot (2.5 m) minimum clearance from
the floor to the bottom of the heater. Refer to the
current edition of CSA−B149 installation compliance
codes.
AIRCRAFT HANGER
1 − In an area where aircraft are housed or serviced, a
10−foot (3 m) minimum clearance from the highest
surface of the aircraft to bottom of the heater must
be maintained.
2 − In other areas, an 8−foot (2.5 m) minimum clearance
from the floor to bottom of heater must be
maintained.
3 − Heaters should be located so that they are
protected from damage from aircraft or other
appliances needed for servicing of aircraft. Refer to
requirements of the enforcing authorities.
In a confined area, the heater must be installed in
accordance with the current edition of CSA−B149
installation compliance codes. Be sure to check with local
codes and ordinances for additional requirements.

Page 4
Additional Requirements
The Commonwealth of Massachusetts stipulates the
following additional requirements:
1 − Gas furnaces shall be installed by a licensed
plumber or gas fitter only.
2 − The gas cock must be T handle" type.
Unit Heater Installation
WARNING
Improper installation, adjustment, alteration, ser-
vice or maintenance can cause property damage,
personal injury or loss of life. Installation and ser-
vice must be performed by a licensed professional
installer (or equivalent), service agency or the gas
supplier.
CAUTION
As with any mechanical equipment, personal injury
can result from contact with sharp sheet metal
edges. Be careful when you handle this equipment.
The appliance shall not be installed downstream from
evaporator coils or cooling units.
Install the unit in the desired location as governed by
clearances, vent connection, air direction, gas supply,
electrical supply and service accessibility.
On LF24 models 100, 115, 145, 175, and 200, mounting
nuts are furnished at the balance point (two positions
only). On LF24 models 230, 250, 300, 345 and 400,
mounting nuts are furnished at each corner of the unit.
Mounting nuts will accommodate 3/8" x 16 threaded rods.
1 − Cut threaded rods to desired length and slide a 3/8"
nut onto the rod.
2 − Slide a flat washer onto the threaded rod AFTER the
nut (7/16" inside diameter X 1" outside diameter X
1/16" thick washer).
3 − Screw the rods (two or four) into the mounting nuts
on the unit.
4 − Tighten nuts to secure unit to rods.
IMPORTANT
Do not use the gas manifold pipe to lift unit. Any ex-
cessive upward or downward force on the manifold
pipe and bracket assembly can cause the ignition
burner and igniter to become misaligned.
TABLE 4
MAXIMUM MOUNTING HEIGHTS
Model Number Feet (Meters)
LF24−100 and LF24−115 16 (4.9)
LF24−145, LF24−175, and
LF24−200 20 (6.1)
LF24−230, LF24−250,
LF24−300, LF24−345 and
LF24−400
30 (9.1)
Combustion and Ventilation Air
Adequate facilities for supplying air for combustion and
ventilation must be provided in accordance with the
current edition of ANSI Z223.1, section 5.3, and
CSA−B149 installation compliance codes, or applicable
provisions of local building codes.
All gas−fired appliances require air to be used for the
combustion process. In many buildings today, there is a
negative indoor air pressure caused by exhaust fans, etc.
If sufficient quantities of combustion air are not available,
the heater or another appliance will operate in an
inefficient manner, resulting in incomplete combustion
which can result in the production of excessive carbon
monoxide.
CAUTION
Insufficient combustion air can cause headaches,
nausea, dizziness, asphyxiation or death.
If indoor air is to be used for combustion, it must be free of
the following substances or the life of the heat exchanger
will be adversely affected: chlorine, carbon tetrachloride,
cleaning solvent, halogen refrigerants, acids, cements
and glues, printing inks, fluorides, paint removers,
varnishes, or any other corrosives.
Rotation of Combustion Air Inducer
(LF24−100, −115 and −145 Only)
The combustion air inducer on LF24 models −100, −115
and −145 may be rotated 90° either to the left or right of the
original vertical position in order to better suit the
application.
NOTE − It is not permissible to rotate the combustion air
inducer on LF24 models −175, −200, −230, −250, −300,
−345 and −400.
Rotate the combustion air inducer assembly as follows:
1 − Remove the heater from the carton. Decide the best
unit heater orientation. The vent can be installed in
one of three discharge positions: up, left, or right.

Page 5
2 − If the inducer is to be rotated, follow the instructions
in this section; otherwise, refer to instructions under
Venting" section.
3 − Before making an electrical or gas connections,
remove the securing screws on the flue
box/combustion air inducer. See figure 1.
FIGURE 1
FLUE BOX AND
COMBUSTION AIR INDUCER ASSEMBLY
VEST PANEL
FLUE BOX GASKET
FLUE BOX
COMBUSTION AIR INDUCER GASKET
COMBUSTION AIR INDUCER
4 − Remove the flue box/combustion air inducer
assembly, ensuring that the gasket is not damaged.
If the gasket is damaged, replace it.
5 − Use a 1/4" socket to remove the three screws which
secure the combustion air inducer to the flue box.
Remove the inducer and gasket from the flue box
ensuring that the gasket is not damaged. If the
gasket is damaged, replace it.
6 − Use the template provided in the back of this manual
to mark new hole locations. Use a 7/32" drill bit to
drill holes in flue box.
7 − Place the gasket between the combustion air
inducer and the flue box. Rotate both the inducer
and the gasket 90° to the desired position. Reinsert
and tighten the three inducer securing screws
(#8−16 X 1/2" HWHSMS).
8 − Place the gasket between the flue box and the vest
panel. Position the flue box/combustion air inducer
assembly on the vest panel. Fasten the flue box to
the vest panel using the flue box securing screws
(#10−16 X 5/8" HWHSMS) and a 5/16" driver.
9 − The unit heater is now ready for installation as
described in the Venting section.
Venting
NOTE − The vent is a passageway, vertical or nearly so,
used to convey flue gases from an appliance, or its vent
connector, to the outside atmosphere. The vent
connector is the pipe or duct that connects a fuel−gas
burning appliance to a vent or chimney.
NOTE − Local codes may supersede any of these
provisions.
GENERAL RECOMMENDATION AND REQUIREMENTS
LF24 unit heaters must be vented in compliance with the
latest edition of the National Fuel Gas Code (NFPA 54 /
ANSI Z223.1) in the USA and with CSA−B149.1 codes in
Canada, as well as applicable provisions of local building
codes, and the following instructions.
A sheet metal flue transition is supplied with this
certified unit. It must not be modified or altered and
must be installed on the outlet of the combustion air
inducer assembly prior to the installation of the vent
connector. Failure to comply with this requirement
will void the certification of the unit by the approval
agencies.
A single−wall vent connector may be used in all
applications between the furnace and the vertical vent
pipe.
A single−wall vent pipe used as a vent connector or as a
vertical vent, must have all seams and joints sealed with
pressure−sensitive aluminum tape or silicone rubber
sealant. Aluminum tape must meet the provisions of
SMACNA AFTS−100−73 Standards. The aluminum tape
must have a temperature rating of 400°F (204°C).
Silicone rubber sealant must have a temperature rating of
482°F (250°C), i.e., Dow Corning RTV−736 or equivalent.
All joints must be secured with at least two corrosion
resistant screws. All joints must be checked for gas
tightness after installation. Single−wall vent pipe used as
vertical vent must not pass through any attic, interior wall,
concealed space, or floor.

Page 6
VERTICAL VENTS USING METAL VENT PIPE
All LF24 unit heaters are listed as Category 1 appliances
for vertical vent installations.
1 − All LF24 unit heaters are to be used with NFPA− or
ANSI−approved chimneys or U.L.−listed type B−1
gas vents where applicable, as well as the
modifications and limitations listed in figure 2. Seal
single−wall vent material according to General
Recommendations and Requirements section.
2 − Keep the vent connector runs as short as possible
with a minimum number of elbows. Refer to the
current edition of ANSI Z223.1 or CSA−B149
installation compliance codes for maximum vent
and vent connector lengths. Horizontal run of the
vent connector from the combustion air inducer
outlet to the chimney/vent pipe cannot exceed the
values in table 6. Single−wall vent connectors shall
not be insulated.
TABLE 5
VENT CONNECTOR DIAMETERS
Model Number Connector Diameter
LF24−100,
LF24−115
LF24−145
4" (102mm)
LF24−175
LF24−200
LF24−230
LF24−250
LF24−300
5" (127mm)
LF24−345
LF24−350
LF24−400*
6" (152mm)
* On LF24−400 models, a minimum 6"(162mm) straight section must be
placed between the flue transition and the first elbow of the vent.
A single 3" (76 mm), 4" (102mm), or 5" (127 mm)
elbow is equivalent to 5 feet (1.53 m) of vent pipe. A
single 6" (152mm) elbow is equivalent to 9 feet (2.75
m) of vent pipe.
Single−wall vent connector shall not be insulated.
3 − All LF24 models may be vented vertically as a single
appliance, or as a common vent with other gas−fired
appliances. In a common venting situation, vent
connectors for other appliances must be joined to
the vent at least 4" (102 mm) above the connected
LF24 connection. When common venting with
another LF24 unit, maintain at least a 4" (102 mm)
vertical separation between the vent connectors.
4 − Clearance to combustible material is 6" (152mm) for
single−wall vent material except where a listed
clearance thimble is used. Clearance to
combustible material for type B−1 vent or
factory−built chimney is per manufacturer’s
instructions.
5 − The vent connector must be supported with hangers
no more than three feet (1 m) apart to prevent
movement after installation. All horizontal vent
connector runs must have a slope up to the vertical
vent of at least 1/4" per foot (1mm per 50mm).
6 − All vertical vents must be terminated with a UL−listed
(or other equivalent agency) vent cap or rain shield
assembly unless local codes permit otherwise.
7 − The vent pipe must extend at least 3 feet (1m) above
the highest point where it passes through a roof of a
building. The vent must also extend at least two feet
higher than any part of a building within a horizontal
distance of 10 feet (3.05 m) unless otherwise
specified by the ANSI Z223.1 or CSA−B149
installation compliance codes. The vent must
extend at least 5 feet (1.53 m) above the highest
connected equipment flue collar.
FIGURE 2
VENT TERMINATION ON SINGLE−WALL VERTICAL VENT RUNS
SINGLE−WALL VENT PIPE WITH
SINGLE−WALL TERMINATION
SINGLE−WALL VENT PIPE WITH
DOUBLE−WALL (TYPE B−1) TERMINATION
ROOF FLASHING
ROOF PITCHED
FROM 0" TO 45"
2" CLEARANCE
THIMBLE
CLEARANCE TO BE
AS SPECIFIED ON
TYPE B" VENT PIPE.
12" MAX
ROOF FLASHING
ROOF PITCHED
FROM 0" TO 45"
SEAL JOINT BETWEEN SINGLE−WALL VENT AND B" VENT TERMINATION
AND THE OPEN SPACE BETWEEN THE SINGLE WALL VENT PIPE AND
THE OUTER PIPE OF THE B" VENT TERMINATION.

Page 7
TABLE 6
MAXIMUM HORIZONTAL VENT CONNECTOR AND
HORIZONTAL VENT PIPE LENGTHS
No. of
Elbows
LF24−100, −115,
−145, −175, and
−200
LF24−230,
−250 and
−300
LF24−345 LF24−400
ft m ft m ft m ft m
1 25 7.6 35 10.7 31 9.4 21 6.4
2 20 6.1 30 9.1 22 6.7 12 3.6
3 15 4.6 25 7.6 13 4.0 3 0.9
4 10 3.0 20 6.1 4 1.2 −− −−
5 5 1.5 15 4.6 −− −− −− −−
6 −− −− 10 3.0 −− −− −− −−
7 −− −− 5 1.5 −− −− −− −−
HORIZONTAL VENTING
NOTE − Common venting is not allowed when horizontally
venting the unit heater.
If the LF24 unit heater is to be horizontally vented, a
positive pressure may be created in the vent. The unit
heater, when installed with horizontal venting, will
perform as a category III appliance.
1 − Special vent materials approved for use with
Category III appliances may be used with these
units. Refer to table 7 for venting components.
2 − If possible, do not terminate the horizontal vent
through a wall that is exposed to prevailing wind.
Exposure to excessive winds can affect unit
performance. If such a termination is necessary,
use a wind block to protect the vent termination from
direct winds.
3 − Vent termination must be free from obstructions and
at least 12" (30.5 cm) above grade level and
maximum snow height.
4 − Do not terminate vent directly below roof eaves or
above a public walkway, or any other area where
condensate dripping may be troublesome and may
cause some staining. Avoid windows where steam
may cause fogging or ice buildup.
5 − Minimum clearance for horizontal vent termination
from any door, window, gravity air inlet, gas or
electric meter, regulators, and relief equipment is 4
feet (1m) for United States installations.
In Canada, horizontal vent termination must have a
minimum 6−foot horizontal clearance from gas and
electric meters and relief devices.
Refer to latest editions of the ANSI Z223.1 or
CSA−B149 for installation compliance codes and
with local authorities with jurisdiction.
6 − Vent termination must be a minimum of 4 feet
(1.2m) horizontally from any soffit or under−eave
vent.
7 − Vent termination must be a minimum of 6 feet (1.83
m) from an inside corner formed by two exterior
walls. If possible, leave a 10−foot clearance.
8 − Vent termination must be a minimum of 10 feet (3m)
from any forced air inlet (includes fresh air inlet for
other appliances, such as a dryer).
9 − For upward sloped vent, a condensate tee and drain
must be installed within the first 5 feet (2m) from the
unit heater to protect the appliance. If a flexible
condensate drain line is used, the drain line must
include a loop filled with water to prevent
combustion products from entering the structure. If
the unit is shut down for an extended period of time
and will be exposed to sub−freezing temperatures,
the condensate may freeze.
10 − For upward sloped vent, see figure 3, condensate
tee and drain must be installed within the first 5 feet
(1.53 m) from the unit heater to protect the
appliance.
11 − Flexible loop trap in condensate line (if used) must
be filled with water to prevent combustion products
from entering structure.
12 − Select a wall termination point that will maintain 1/4"
rise per foot slope of horizontal run of vent pipe. In
areas where authorities having jurisdiction permit, a
downward slope of maximum 1/4" per foot is also
acceptable. Condensate drainage can be collected
in a tee pipe section (figure 4) with drain loop similar
to one used for upward slope vent, or allowed to drip
through the vent termination, if permitted by
authorities (figure 5).
13 −For horizontal venting, the vent pipe must be
supported with hangers no more than 3 feet (1m)
apart to prevent movement after installation.
14 − All horizontal vent applications which use Category
III vent pipe must terminate with an approved
Category III tee. Opening end must face downward.
15 − When termination is routed through an exterior
combustible wall, the vent must be supported using
a listed clearance thimble. Inside edge of vent
termination tee or elbow must be at least 12"
(305mm) from outside wall.

Page 8
FIGURE 3
HORIZONTAL VENTING
COMBUSTION AIR INDUCER
CAN BE ROTATED ON UNITS
LF24−100, −115 and −145 ONLY.
NOTE − FOR LF24−175, −200,
−230, −250 −250, −300, −345 and
400. DO NOT ROTATE THE
COMBUSTION AIR INDUCER;
USE 90°ELBOW.
COMBUSTION
AIR INDUCER 12 INCHES
MIN.
(30.5 CM)
VENT
TERMINATION
TEE OR 90°
ELBOW
12" (30.5CM)
MINIMUM ABOVE
HIGHEST
SNOWFALL
DRAIN LOOP WITH
WATER TRAP TO
CONDENSATE TRAP
(Provided by installer) GROUND LEVEL
UPWARD SLOPE
NOTE − Minimum horizontal length
equals 5 feet (1.53 m). This does not
include termination tee. Refer to
table 6 for maximum length and
number of elbows.
CATEGORY III
ADAPTER
(Make airtight using
high−temperature
sealant provided in kit)
LISTED WALL
THIMBLE
THROUGH
COMBUSTIBLE
WALL
Venting may be single−wall (26
GSG) galvanized or equivalent
stainless steel vent pipe sealed
per these instructions, OR listed
special vent for Category III
appliances.
SLOPE = 1/4 IN. PER FOOT
RUN MAXIMUM.
FIGURE 4
CONDENSATE DRAIN THROUGH TEE PIPE AND DRAIN LOOP
TEE PIPE
SECTION
DOWNWARD SLOPE ON HORIZONTAL VENT
12 INCHES
(30.5 cm)
MINIMUM
VENT TERMINATION
TEE OR 90° ELBOW
NOTE − Minimum horizontal
length equals 5 feet (1.53 m).
This does not include termination
tee. Refer to table 6 for maximum
length and number of elbows.
Venting may be single−wall (26
GSG) galvanized or equivalent
stainless steel vent pipe sealed
per these instructions, OR listed
special vent for Category III
appliances.
SLOPE = 1/4 IN. PER FOOT
RUN MAXIMUM.
DRAIN LOOP WITH
WATER TRAP TO
CONDENSATE TRAP
(Provided by installer)

Page 9
FIGURE 5
CONDENSATE DRAIN THROUGH VENT TERMINATION
DOWNWARD SLOPE ON HORIZONTAL VENT
12 INCHES
(30.5 cm)
MINIMUM
VENT TERMINATION
TEE OR 90° ELBOW
NOTE − Minimum horizontal
length equals 5 feet (1.53 m). This
does not include termination tee.
Refer to table 6 for maximum
length and number of elbows.
DOUBLE
MALE
ADAPTER
(Cat III kits
only)
Venting may be single−wall (26 GSG)
galvanized or equivalent stainless
steel vent pipe sealed per these
instructions, OR listed special vent
for Category III appliances.
SLOPE = 1/4 IN. PER FOOT RUN
MAXIMUM.
TABLE 7
Category III Horizontal Venting Components
(Required for Horizontal Vent Applications)
Unit Catalog Number Model Number Description
LF24−100
LF24−115
LF24−145
75W63 C5VENT4KU 4" upward sloped Cat III vent kit
75W67 C5VENT4KD 4" downward sloped Cat III vent kit
75W71 C5VENT4E 4" 90° elbow Cat III (optional)
75W77 C5VENT4P6 4" straight pipe (length = 6")
75W78 C5VENT4P6 4" straight pipe (length = 12")
75W79 C5VENT4P6 4" straight pipe (length = 36")
LF24−175
LF24−200
LF24−230
LF24−250
LF24−300
75W64 C5VENT5KU 5" upward sloped Cat III vent kit
75W68 C5VENT5KD 5" downward sloped Cat III vent kit
75W72 C5VENT5E 5" 90° elbow Cat III (optional)
75W80 C5VENT5P6 5" straight pipe (length = 6")
75W81 C5VENT5P12 5" straight pipe (length = 12")
75W82 C5VENT5P36 5" straight pipe (length = 36")
LF24−345
LF24−400
75W65 C5VENT6KU 6" upward sloped Cat III vent kit
75W69 C5VENT6KD 6" downward sloped Cat III vent kit
75W73 C5VENT6E 6" 90° elbow Cat III (optional)
75W83 C5VENT6P12 6" straight pipe (length = 12")
75W84 C5VENT6P36 6" straight pipe (length = 36")

Page 10
Electrical Connections
NOTE − Local codes may supersede any of the provisions
outlined in this instruction.
The LF24 series unit heaters use a direct spark ignition
system. There is no pilot necessary as the spark lights the
main burner as the gas valve is turned on. The direct
spark ignition control board emits radio noise as the
sparking process is under way. The level of energy may
be sufficient to disturb a logic circuit in a microprocessor
controlled thermostat. It is recommended that an isolation
relay be used when connecting the LF24 series unit
heaters to a microprocessor−controlled thermostat. Install
the thermostat according to instructions provided by the
manufacturer. Install a separate fused disconnect switch,
with the fuse sized according to blower motor size.
Connect wiring through knockout on the junction box
located on the side of the unit heater. Refer to heater
wiring diagram for connection information. Use 18 gauge
wire or larger for thermostat connections.
NOTE − Electrically ground unit in accordance with local
codes or, in the absence of local codes, in accordance
with the current National Electrical Code (ANSI/NFPA No.
70) in the U.S.A., and in Canada with the current
Canadian Electrical Code, Part 1 (CSA C22.1).
NOTE − Uninsulated ground wires must be wrapped in
electrical tape to avoid damage to the electrical system.
Connect field wiring as shown on wiring diagram on unit.
Also refer to typical diagram in this manual. An additional
thermostat wire must be run to terminal G"on heater
when continuous blower is desired.
TYPICAL LF24 WIRING SCHEMATIC

Page 11
Gas Connection
When connecting gas supply, the length of the run from
the meter must be considered in determining the pipe size
to avoid excessive pressure drop. A line pressure of 7"
w.c. (178 mm w.c.) for natural gas should be maintained
when sizing piping. For correct sizing of piping, consult
the utility having jurisdiction.
A drip leg should be installed in the vertical pipe run to the
unit. In some localities, codes may require that a manual
main shutoff valve and union (furnished by installer) be
installed external to the unit. Union must be of the ground
joint type. See figure 6.
A 1/8" NPT plugged tap must be installed immediately
upstream of the gas supply connection to the heater.
NOTE − Compounds used on threaded joints of gas piping
must be resistant to the actions of liquefied petroleum
gases.
FIGURE 6
GROUND
JOINT UNION
DRIP LEG
MANUAL
MAIN SHUT−OFF VALVE
(Furnished by Installer)
GAS FLOW
1/8 NPT
PLUGGED
TAP
GAS SUPPLY CONNECTION
Leak Check
After gas piping is completed, carefully check all piping
connections, (field and factory), for gas leaks. Use a soap
solution or other preferred means.
CAUTION
DO NOT use matches, candles, flame or other
sources of ignition to check for gas leaks.
The appliance must be isolated from the gas supply
piping system by closing its individual manual gas shutoff
valve during any pressure testing of the gas supply
system at test pressures equal to or less than 1/2 psig
(3.45kPa).
IMPORTANT
The heater and its individual shut off valve must be
disconnected from the gas supply piping system
during any pressure testing of that system at test
pressures in excess of 1/2 psig (3.45kPa). See fig-
ure 7.
NOTE − In case emergency shutdown is required, shut
down main gas valve and disconnect main power to unit.
These devices should be properly labeled by the installer.
FIGURE 7
CAP
GAS SUPPLY TO UNIT HEATER
UNIT HEATER
MANUAL MAIN SHUT−OFF
VALVE WILL NOT HOLD
NORMAL TEST
PRESSURES OF 1/2 psig
(3.45kPa) OR HIGHER
DISCONNECT GAS
VALVE WHEN TEST
PRESSURES OF
1/2 psig (3.45kPa)
OR HIGHER WILL
BE USED.
Unit Start−Up
FOR YOUR SAFETY READ BEFORE LIGHTING
WARNING
Electric shock hazard. Can cause injury
or death. Do not use this appliance if
any part has been under water. Immedi-
ately call a qualified service technician
to inspect the furnace and to replace
any part of the control system and any
gas control which has been under wa-
ter.
WARNING
Danger of explosion. Can cause injury
or product or property damage. 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.

Page 12
WARNING
Electric shock hazard. Can cause injury
or death. Before attempting to perform
any service or maintenance, turn the
electrical power to unit OFF at
disconnect switch(es). Unit may have
multiple power supplies.
WARNING
Danger of explosion and fire. Can cause
injury or product or property damage.
You must follow these instructions
exactly.
BEFORE LIGHTING 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.
These unit heaters are equipped with an automatic spark
ignition system. There is no pilot. In case of a safety
shutdown, move thermostat switch to OFF, then return
the thermostat switch to HEAT position.
GAS VALUE OPERATION FOR HONEYWELL
VR8205/VR8305 SERIES GAS VALVE (FIGURE 8)
1 − STOP! Read the safety information at the beginning
of this section.
2 − Set thermostat to lowest setting.
3 − Turn off all electrical power to appliance.
4 − This appliance is equipped with an ignition device
which automatically lights burners. DO NOT
attempt to light the burners manually.
5 − Turn the manual knob on gas valve clockwise to
OFF. Do not force.
6 − Wait five minutes to clear out any gas. If you then
smell gas, STOP! Immediately call your
gas supplier from a neighbor’s phone. Follow the
gas supplier’s instructions. If you do not smell
gas, go to next step.
7 − Turn manual knob on gas valve counterclockwise
to ON.
8 − Turn on all electric power to unit.
9 − Set thermostat to desired setting.
10 − The combustion air inducer will start. The burners
will light within 40 seconds.
11 − If unit does not light first time (gas line not fully
purged) it will attempt up to two more ignitions
before locking out.
12 − If lockout occurs, repeat steps 1 through 8.
13 − If appliance still will not operate, follow the
instructions To Turn Off Gas to Unit" and call your
service technician or gas supplier.
ON
OFF
FIGURE 8
HONEYWELL VR8205/VR8305 SERIES GAS VALVE
GAS VALVE SHOWN IN OFF POSITION
MANIFOLD PRESSURE ADJUSTMENT SCREW
INLET
PRESSURE
TAP
MANIFOLD
PRESSURE
TAP

Page 13
To Turn Off Gas to Unit
1 − Set thermostat to lowest level.
2 − Turn off all electrical power to unit if service is to be
performed.
3 − Turn knob on gas valve 90° clockwise to OFF.
Heating Sequence of Operation
1 − When the thermostat calls for heat, the combustion
air inducer starts immediately.
2 − Combustion air pressure switch proves inducer
operation before allowing power to the ignition
controller. This switch is factory−set and no
adjustment is necessary.
3 − After prepurge of approximately 30 seconds, the
spark ignition is energized and the solenoid valves
open in the gas valve. LF24 models 230, 250, 300,
345 and 400 are equipped with a step opening
valve. During ignition phase of start−up a pressure of
approximately 25% of full rate allows even ignition
of all burners for several seconds before full rate
pressure is established.
4 − The spark then ignites the gas, the ignition sensor
proves the flame, and the combustion process
continues.
5 − In the event that the flame is not detected after the
first 10−second trial for ignition, the controller will
repeat steps 3 and 4 an additional two times before
locking out the gas valve. Ignition control will then
automatically repeat steps 3, 4, and 5 after 60
minutes.
NOTE: To interrupt the 60−minute lockout period, move
thermostat from Heat"to OFF"then back to Heat."
Heating sequence then restarts at step 1.
6 − The burners must light without noticeable crossover
delay. There must be no flame lifting from the burner
heads, flashback or burning within the burner. The
flames should be predominantly blue in color and
should be approximately centered in the tubes with
no apparent impingement taking place.
7 − The ignition control will energize the fan(s)
approximately 45 seconds after ignition is
established.
8 − After the thermostat demand is satisfied, the gas
valve is closed. Five seconds after the demand is
satisfied, the combustion air inducer is shut off.
9 − The ignition control must shut off the system fan
approximately 150 seconds after the gas valve is
de-energized.
Ignition Control LED
The ignition control contains a green LED which indicates
the following:
TABLE 8
IGNITION CONTROL LED
LED UNIT OPERATION
Slow
Flash* Normal Operation − No call for heat
Fast
Flash Normal Operation − Call for heat
2
Flashes
System lockout − failed to detect or sustain
flame
3
Flashes
Pressure switch failed closed before CAI is en-
ergized or failed open after CAI is energized
4
Flashes High limit or rollout switch open
5
Flashes Flame sensed and gas valve not energized
Steady
Off Loss of power
Steady
On Ignition control failure
*When thermostat is placed in continuous fan mode, LED will
slowly flash.
High Altitude Adjustment
In Canada, certification for installation at altitudes over
4500 feet (1372m) above sea level is the jurisdiction of the
local authorities.
Unit may be fired at full input up to 2000 feet (610m) above
sea level. Above 2000 feet (610m), manifold pressure
must be adjusted on some units. Adjust pressure
regulator to pressure shown in table 9 for natural gas and
table 10 for LP/propane gas.
In some cases, it is necessary to change the pressure
switch to ensure proper operation at higher altitudes. See
table 1.
NOTE − A natural to LP/propane gas changeover kit is
required to convert the unit in the field. Refer to the
installation instructions supplied with the changeover kit
for conversion procedure.
If unit is installed at an altitude greater than 7500 feet
(2286m), unit must be derated by four percent for each
additional 1000 feet (305m) above 7500 feet (2286m).
The combustion air inducer proving switch is factory set
and no adjustment is necessary.

Page 14
TABLE 9
NATURAL GAS MANIFOLD PRESSURES − in. w.g. (kPa)
LF24
UNIT
ALTITUDE – FEET (METERS)
0−2000
(0−610)
2001− 2500
(610−762)
2501 −3500
(763−1067)
3501 − 4500
(1067−1372)
4501 − 5500
(1372−1676)
5501 − 6500
(1677−1981)
6501 − 7500
(1981−2286)
LF24−100**
LF24−115**
LF24−300
3.5
(0.87)
3.5
(0.87)
3.5
(0.87)
3.5
(0.87)
3.4
(0.84)
3.3
(0.82)**
3.2
(0.79)**
LF24−145** 3.5
(0.87)
3.4
(0.84)
3.3
(0.82)
3.2
(0.79)
3.1
(0.77)
3.0
(0.74)**
2.9
(0.72)**
LF24−175*
LF24−230
3.5
(0.87)
3.5
(0.87)
3.5
(0.87)*
3.5
(0.87)*
3.5
(0.87)*
3.5
(0.87)*
3.5
(0.87)*
LF24−200
LF24−250
LF24−345
LF24−400
3.5
(0.87)
3.5
(0.87)
3.5
(0.87)
3.4
(0.84)
3.3
(0.82)
3.2
(0.79)
3.1
(0.77)
* The LF24−175 unit requires pressure switch change when installed at elevations above 2500 feet (762m). Order pressure switch 36W49. No
adjustment to switch is required.
* LF24 models −100, −115 and −145 require pressure switch change when installed at elevations above 5500 feet (1676m). Order pressure switch
36W49. No adjustment to switch is required.
TABLE 10
LP/PROPANE GAS MANIFOLD PRESSURES − in. w.g. (kPa)
LF24
UNIT
ALTITUDE – FEET (METERS)
0−2000
(0−610)
2001− 2500
(610−762)
2501 −3500
(763−1067)
3501 − 4500
(1067−1372)
4501 − 5500
(1372−1676)
5501 − 6500
(1677−1981)
6501 − 7500
(1981−2286)
LF24−100**
LF24−115**
LF24−300
9.0
(2.24)
9.0
(2.24)
9.0
(2.24)
9.0
(2.24)
8.7
(2.16)
8.4
(2.09)**
8.1
(2.01)**
LF24−145** 9.0
(2.24)
8.7
(2.16)
8.4
(2.09)
8.1
(2.01
7.8
(1.94)
7.5
(1.86)**
7.2
(1.79)**
LF24−175*
LF24−230
9.0
(2.24)
9.0
(2.24)
9.0
(2.24)*
9.0
(2.24)*
9.0
(2.24)*
9.0
(2.24)*
9.0
(2.24)*
LF24−250 9.0
(2.24)
9.0
(2.24)
9.0
(2.24)
8.7
(2.16)
8.4
(2.08)
8.1
(2.01)
7.8
(1.94)
LF24−200
LF24−345
LF24−400
9.5
(2.37)
9.5
(2.37)
9.5
(2.37)
9.2
(2.28)
8.9
(2.21)
8.6
(2.13)
8.3
(2.06)
* The LF24−175 unit requires pressure switch change when installed at elevations above 2500 feet (762m). Order pressure switch 36W49. No
adjustment to switch is required.
* LF24 models −100, −115 and −145 require pressure switch change when installed at elevations above 5500 feet (1676m). Order pressure switch
36W49. No adjustment to switch is required.

Page 15
Gas Flow
To check for proper gas flow to the combustion chamber,
determine the Btu input from the appliance rating plate.
Divide this input rating by the Btu per cubic feet of
available gas. Result is the required number of cubic feet
per hour. Determine the flow of gas through the gas meter
for two minutes and multiply by 30 to get the hourly flow of
gas.
Gas Pressure Adjustment
1 − Check gas line pressure with unit firing at maximum
rate. A minimum of 5" (127mm) w.c. for natural gas
or 11" (279mm) w.c. for LP/propane gas should be
maintained for proper unit operation.
2 − After line pressure has been checked and adjusted,
check regulator pressure. Adjust manifold pressure
to values specified on the unit rating plate. See
figures 8, 9, and 10 for gas pressure adjustment
screw location. A natural gas to LP/propane gas
changeover kit is required to convert unit in the field.
Refer to installation instructions provided with
changeover kit for conversion procedure.
Limit Control Switch
The limit control switch(es) are factory−set and are not
field−adjustable.
Louver Vane Adjustment
The LF24 series unit heaters are provided with adjustable
louver vanes. Air flow from the unit can be directed down,
straight, out, up, or any combination of these.
WARNING
DO NOT CLOSE the bottom three lou-
vers on LF24. Premature failure to the
heat exchanger can occur.
Combustion Air Pressure Switch
This pressure switch checks for proper combustion air
inducer operation before allowing an ignition trial. The
switch is factory−set and no field adjustment is necessary.
Service
CAUTION
Turn off gas and electrical power to unit before per-
forming any maintenance or service operations on
this unit. Remember to follow lighting instructions
when putting unit back into operation after service
or maintenance.
The unit heater and vent system shall be inspected once a
year by a licensed professional service technician, or
equivalent.
LUBRICATION
1 − Combustion air inducer motor bearings are
pre−lubricated and sealed. No further lubrication is
necessary.
2 − Fan motor bearings should be lubricated according
to manufacturer’s instructions on each motor. If no
instruction is provided, use the following as a guide:
motors with oiling ports are pre−lubricated for an
extended bearing life, re−lubricate with a few drops
of SAE No. 10 non−detergent oil once every two
years.
BURNERS
1 − Periodically examine burner flames for proper
appearance during the heating season.
2 − Before each heating season examine the burners
for any deposits or blockage that may have
occurred.
3 − Clean burners as follows:
a − Turn off both electrical and gas supplies to unit.
b − Disconnect gas supply piping, high tension and
sensor leads. Remove gas manifold. Remove
burner tray.
c − Clean burners as necessary. Make sure that
burner heads line up properly to ensure flame
crossover. Check spark gap on electrode and
adjust if required. The gap should be between
0.110" and 0.140" (2.8 mm to 3.6 mm). The gap
may be checked with appropriately sized twist
drills or feeler gauges.
d − Reinstall burner tray, gas manifold, high
tension and sensor leads. Reconnect gas
supply piping.
e − Restore electrical power and gas supply.
Follow lighting instructions to light unit. Check
burner flame.

Page 16
FLUE PASSAGEWAY AND FLUE BOX
The flue passages and flue box should be inspected and
cleaned prior to each heating season. The sequence of
operation should be as follows:
1 − Turn off both electrical and gas supply to unit.
2 − Disconnect combustion air inducer wiring.
3 − Remove screws securing flue box to unit. Remove
flue box. If necessary, remove blower assembly
from flue box. Clean flue box with wire brush.
4 − Remove baffle retention bracket and flue baffles.
Clean flue baffles with wire brush.
5 − Remove burners as described in Burners" section.
6 − Clean tubes with a wire brush.
7 − Reassemble unit. The combustion air and flue box
gaskets should also be replaced during
reassembly.
8 − Restore electrical power and gas supply. Follow
lighting instructions to light unit. Check operation of
unit.
COMBUSTION AIR INDUCER
Under normal operating conditions, the combustion air
inducer should be checked and cleaned prior to the
heating season with the power supply disconnected. Use
a small brush to clean inducer wheel.
ELECTRICAL
1 − Check all wiring for loose connections.
2 − Check for correct voltage at unit (unit operating).
3 − Check amperage draw.
FLUE AND CHIMNEY
Check all vent and vent connector joints for tightness.
Ensure that connections are sealed and that there are no
blockages.
FAILURE TO OPERATE
If unit fails to operate check the following:
1 − Is thermostat calling for heat?
2 − Is main disconnect closed?
3 − Is there a breaker tripped or a fuse blown?
4 − Is gas turned on at meter?
5 − Is manual shutoff valve open?
6 − Is unit ignition system in lock out? If unit locks out
again, call service technician to inspect unit.
7 − Is pressure switch closed? Obstructed flue will
cause unit to shut off at pressure switch. Check flue
passage and outlet.
SAFETY SHUT−OFF VALVE TEST
The safety shut−off valve test procedure is as follows:
1 − Turn off the manual gas valve.
2 − Set the thermostat to call for heat.
3 − System begins normal sequence of operation.
4 − After approximately 30 seconds (pre purge period)
the LED will fast flash indicating the gas valve is
powered.
5 − After 10 seconds, the gas valve closes and steps 4
and 5 will repeat two additional times before locking
out the gas valve, which will be indicated by two
flashes on the LED.
6 − To restart the system, de−energize the thermostat
call for heat and follow the operating instructions
under Unit Start−Up".
REPAIR PARTS
When ordering repair parts include the complete unit
model number listed on the unit rating plate. For example:
LF24−175A−1.
Electrical Connections Tight?
START−UP AND PERFORMANCE CHECKLIST
Job No.:
City:
City:
Serial No.:
Date:
State/Province:
Service Technician:
Air Shutters Properly Adjusted (If Installed)?
Flue Connections Tight?
THERMOSTAT
Calibrated?
Heat Anticipator Properly Set?
Level?
Manifold Pressure
Blower Motor Amps
Blower Motor Lubrication O.K.?
Gas Piping Connections Tight & Leak−Tested?
State/Province:
Fan Timer Operation Checked?
w.c.
Job Name:
Job Location:
Installer:
Unit Model No.:
Supply Voltage
Furnace Btu Input
Line Pressure

Page 17
TEMPLATE
Location of Combustion Air Inducer Mounting Holes for
Rotated Inducer
EXISTING HOLE
EXISTING HOLE
EXISTING HOLE