Modine Manufacturing DFP Manual

5-564
CAUTION
To prevent premature heat exchanger failure do
not locate ANY gas-fired units in areas where
chlorinated, halogenated, or acid vapors are
present in the atmosphere.
December, 2008
INSTALLATION AND SERVICE MANUAL
gas-fired indoor power vented duct furnaces
model DFP
5-564
5H080637A
THIS MANUAL IS THE PROPERTY OF THE OWNER.
PLEASE BE SURE TO LEAVE IT WITH THE OWNER WHEN YOU LEAVE THE JOB.
FOR YOUR SAFETY
The use and storage of gasoline or other
flammable vapors and liquids in open containers
in the vicinity of this appliance is hazardous.
FOR YOUR SAFETY
IF YOU SMELL GAS:
1. Open windows.
2. Don’t touch electrical switches.
3. Extinguish any open flame.
4. Immediately call your gas supplier.
Inspection on Arrival
1. Inspect unit upon arrival. In case of damage, report it
immediately to transportation company and your local factory
sales representative.
2.
Check rating plate on unit to verify that power supply meets
available electric power at the point of installation.
3. Inspect unit upon arrival for conformance with description of
product ordered (including specifications where applicable).
IMPORTANT
The use of this manual is specifically intended
for a qualified installation and service agency.
A qualified installation and service agency must
perform all installation and service of these
appliances.
WARNING
Improper installation, adjustment, alteration,
service or maintenance can cause property
damage, injury or death, and could cause
exposure to substances which have been
determined by various state agencies to cause
cancer, birth defects or other reproductive
harm. Read the installation, operating and
maintenance instructions thoroughly before
installing or servicing this equipment.
All models approved for use in California by the CEC
CUS

5-564
2
SPECIAL PRECAUTIONS
THE INSTALLATION AND MAINTENANCE INSTRUCTIONS
IN THIS MANUAL MUST BE FOLLOWED TO PROVIDE SAFE,
EFFICIENT AND TROUBLE-FREE OPERATION. IN ADDITION,
PARTICULAR CARE MUST BE EXERCISED REGARDING
THE SPECIAL PRECAUTIONS LISTED BELOW. FAILURE
TO PROPERLY ADDRESS THESE CRITICAL AREAS COULD
RESULT IN PROPERTY DAMAGE OR LOSS, PERSONAL
INJURY, OR DEATH. THESE INSTRUCTIONS ARE SUBJECT
TO ANY MORE RESTRICTIVE LOCAL OR NATIONAL CODES.
HAZARD INTENSITY LEVELS
1. DANGER: Indicates an imminently hazardous situation which,
if not avoided, WILL result in death or serious injury.
2. WARNING: Indicates a potentially hazardous situation which, if
not avoided, COULD result in death or serious injury.
3. CAUTION: Indicates a potentially hazardous situation which,
if not avoided, MAY result in minor or moderate injury.
4. IMPORTANT: Indicates a situation which, if not avoided,
MAY result in a potential safety concern.
2
SPECIAL PRECAUTIONS / TABLE OF CONTENTS
DANGER
Appliances must not be installed where they may be
exposed to a potentially explosive or flammable atmosphere.
WARNING
1. Gas fired heating equipment must be vented - do not operate
unvented.
2. A built-in power exhauster is provided - additional external
power exhausters are not required or permitted.
3. If you are replacing an existing heater, it may be necessary to
resize the venting systems. Improperly sized venting systems
can result in vent gas leakage or the formation of condensate.
Refer to the National Fuel Gas Code ANSI Z223.1 or CSA
B149.1 latest edition. Failure to follow these instructions can
result in injury or death.
4. Under no circumstances should two sections of double wall
vent pipe be joined together within one horizontal vent system
due to the inability to verify complete seal of inner pipes.
5. All field gas piping must be pressure/leak tested prior to
operation. Never use an open flame. Use a soap solution or
equivalent for testing.
6. Gas pressure to appliance controls must never exceed 14"
W.C. (1/2 psi).
7. Disconnect power supply before making wiring connections
to prevent electrical shock and equipment damage.
8. All appliances must be wired strictly in accordance with
wiring diagram furnished with the appliance. Any wiring
different from the wiring diagram could result in a hazard
to persons and property.
9. To reduce the opportunity for condensation, the minimum
sea level input to the appliance, as indicated on the serial
plate, must not be less than 5% below the rated input, or
5% below the minimum rated input of duel rated units.
10. Ensure that the supply voltage to the appliance, as
indicated on the serial plate, is not 5% greater than the
rated voltage.
11. Any original factory wiring that requires replacement must
be replaced with wiring material having a temperature
rating of at least 105°C.
12.
When servicing or repairing this equipment, use only factory-
approved service replacement parts. A complete replacement
parts list may be obtained by contacting Modine Manufacturing
Company. Refer to the rating plate on the appliance for
complete appliance model number, serial number, and
company address. Any substitution of parts or controls not
approved by the factory will be at the owners risk.
Table of Contents
Inspection on Arrival ................................................................. 1
Special Precautions.................................................................. 2
SI (Metric) Conversion Factors................................................. 3
Unit Location............................................................................. 3
Location Recommendations.............................................. 3
Combustible Material and Service Clearances ................. 3
Combustion Air Requirements........................................... 3
Unit Suspension ....................................................................... 4
Installation ................................................................................ 4
Direction of Airflow............................................................. 4
Duct Installation and Airflow Distribution ........................ 4-5
Venting ........................................................................... 5-6
Gas Connections............................................................... 7
Electrical Connections....................................................... 8
Start-Up Procedure................................................................... 8
Pilot Burner and Main Burner Adjustment ......................... 9
Air Shutter Adjustment..................................................... 10
Control Operating Sequence...................................... 11-13
Variable Air Movement Applications ................................ 13
Gas Control Options................................................... 13-14
Dimensional Data ................................................................... 15
Performance........................................................................... 16
Air Temperature and External Static Pressure Limits...... 16
Pressure Drop Curves............................................................ 17
Maintenance........................................................................... 18
Manifold Assembly Removal ........................................... 18
Burner and Pilot Assembly Removal .......................... 18-19
Service & Troubleshooting................................................. 20-21
Replacement Parts Ordering.................................................. 22
Model Identification................................................................. 22
Commercial Warranty................................................Back Page
CAUTION
1. Purging of air from gas lines should be performed as
described in ANSI Z223.1 - latest edition “National Fuel Gas
Code”, or in Canada in CAN/CGA-B149 codes.
2. Do not attempt to reuse any mechanical or electrical
controllers which have been wet. Replace defective controller.
3. Ensure that the supply voltage to the application, as indicated
on the serial plate, is not 5% less than the rated voltage.
IMPORTANT
1. To prevent premature heat exchanger failure, do not locate
ANY gas-fired appliances in areas where corrosive vapors
(i.e. chlorinated, halogenated or acid) are present in the
atmosphere.
2. To prevent premature heat exchanger failure, the input to
the appliance, as indicated on the serial plate, must not
exceed the rated input by more than 5%.
3. To prevent premature heat exchanger failure, observe heat
exchanger tubes by looking at the heat exchanger through
field installed access openings in connecting ductwork. If
the bottom of the tubes become red while blower and duct
furnace are in operation, additional baffles must be inserted
between blower and duct furnace to assure uniform air flow
across the heat exchanger.
4. To prevent premature heat exchanger failure, with all control
systems, a blower starting mechanism must be provided so
that the blower is running or energized within 45 seconds of
the gas control operation.
5. Start-up and adjustment procedures should be performed
by a qualified service agency.
6. To check most of the Possible Remedies in the troubleshooting
guide listed in Table 20.1, refer to the applicable sections
of the manual.

5-564
UNIT LOCATION
Location Recommendations
1. When locating the furnace, consider general space and
heating requirements, availability of gas and electrical
supply, and proximity to vent locations.
2. Unit must be installed on the positive pressure side of the
circulating blower.
3. Be sure the structural support at the unit location site is
adequate to support the weight of the unit. For proper
operation the unit must be installed in a level horizontal
position.
4. Do not install units in locations where the flue products
can be drawn into the adjacent building openings such as
windows, fresh air intakes, etc.
5. Be sure that the minimum clearances to combustible
materials and recommended service clearances are
maintained. Units are designed for installation on non-
combustible surfaces with the minimum clearances shown
in Figure 3.1 and Tables 3.2 and 3.3.
6. Units installed downstream of refrigeration systems, or
exposed to inlet air temperatures of 40°F or less, may
experience condensation, therefore, provisions should
be made for disposal of condensate. Means have been
provided in the bottom pan of the unit to accommodate a
condensate drain line connection flange.
7. When locating units, it is important to consider that the
exhaust vent piping must be connected to the outside
atmosphere.
8. In garages or other sections of aircraft hangars such as
offices and shops which communicate with areas used for
servicing or storage, keep the bottom of the unit at least 7”
above the floor. In public garages, the unit must be installed
in accordance with the Standard for Parking Structures
NFPA #88A and the Standard for Repair Garages NFPA
#88B. In Canada, installation of unit heaters in airplane
hangars must be in accordance with the requirements of
the enforcing authority, and in public garages in accordance
with the current CAN/CGA-B149 codes.
9. Do not install units in locations where gas ignition system is
exposed to water spray, rain, or dripping water.
33
SI (METRIC) CONVERSION FACTORS / UNIT LOCATION
DANGER
Appliances must not be installed where they may be exposed
to a potentially explosive or flammable atmosphere.
SI (METRIC) CONVERSION FACTORS
Table 3.1
Recommended
Service
Clearance
Model Access Non-Access Top Bottom
Size Side Side (C) (D)
(A) (B)
75 18" 6" 10" 0"
100/125 20" 6" 10" 0"
150/175 25" 6" 10" 0"
200/225 27" 6" 10" 0"
250/300 30" 6" 10" 0"
350/400 41" 6" 10" 0"
IMPORTANT
To prevent premature heat exchanger failure, do not locate
ANY gas-fired appliances in areas where corrosive vapors (i.e.
chlorinated, halogenated or acid) are present in the atmosphere.
C
B
A
D"
Access
Slide
To Convert Multiply By To Obtain
"W.C. 0.24 kPa
psig 6.893 kPa
°F (°F-32) x 0.555 °C
inches 25.4 mm
feet 0.305 meters
CFM 0.028 m3/min
To Convert Multiply By To Obtain
CFH 1.699 m3/min
Btu/ft30.0374 mJ/m3
pound 0.453 kg
Btu/hr 0.000293 kW/hr
gallons 3.785 liters
psig 27.7 "W.C.
Clearance to
Combustible Materials
Model Access Non-Access Top Bottom
Size Side Side (C) (D)
(A) (B)
75 12" 1" 3" 2"
100/125 12" 1" 3" 2"
150/175 12" 1" 3" 2"
200/225 12" 2" 3" 2"
250/300 12" 2" 3" 2"
350/400 12" 2" 3" 2"
Figure 3.1 - Combustible Material and Service
Clearances
Combustion Air Requirements
Units installed in tightly sealed buildings or confined spaces
must be provided with two permanent openings, one near
the top of the confined space and one near the bottom. Each
opening should have a free area of not less than one square
inch per 1,000 BTU per hour of the total input rating off all
units in the enclosure, freely communicating with interior areas
having, in turn adequate infiltration from the outside.
For further details on supplying combustion air to a confined
(tightly sealed) space or unconfined space, see the National
Fuel Gas Code ANSI Z223.1 of CAN/CGA B149.1 or .2
Installation Code, latest edition.
➀A 3'' minimum clearance to combustible material is required from the vent collar.
Table 3.2 - Combustible Material Clearances
Table 3.3 - Service Clearances

5-564
UNIT SUSPENSION
Be sure the means of suspension is adequate to support the
weight of the unit (see Dimensional Data for unit weights). For
proper operation, the unit must be installed in a level horizontal
position. Combustible material and service clearances as
specified in Figure 3.1 and Tables 3.2 and 3.3 must be strictly
maintained.
1. Four 1/2" - 13NC tapped holes in top of furnace are provided
to accept ceiling hangers. To assure that flames are directed
into the center of the heat exchanger tubes, the furnace must
be supported in a vertical position. Use a spirit level to ensure
that unit is suspended correctly.
2. NOTE: A pipe hanger adapter kit, shown in Figure 4.1, is
available as an accessory. One kit consists of two drilled
3/4" IPS pipe caps and two 1/2 - 13 x 1-3/4" capscrews to
facilitate threaded pipe suspension. Two kits are required for
mounting all duct furnace models.
Figure 4.1 - Suspension Methods
INSTALLATION
Direction of Airflow
Select proper direction of airflow. The air baffle must face the
air inlet direction as shown in Figure 4.2. If it is necessary to
reverse the airflow direction, remove the four screws securing
the air distribution baffle, reverse the air distribution baffle to the
air inlet side and replace the screws. See Airflow Reversal Note.
Figure 4.2 - Air Distribution Baffle Location
Baffle location shown on entering air side of duct furnace.
Airflow Reversal Note: If factory installed discharge air options
(thermostat, freeze protection, etc.) were provided, these
options would have to be relocated to the discharge air side of
the duct furnace.
Duct Installation
1. The furnace is designed to accept straight ductwork. See
Figure 4.3. Provide an airtight seal between the ductwork
and the furnace. Seams with cracks in ductwork should be
caulked and/or taped and be of permanent type. All duct
connections MUST be airtight to prevent air leakage.
2. Provide removable access panels on both the upstream and
downstream sides of the ductwork; see Figure 4.3. These
openings should be large enough to view smoke or reflect
light inside the casing to indicate leaks in the heat exchanger
and to check for hot spots on heat exchangers due to poor air
distribution or lack of sufficient air (CFM)
Figure 4.3 - Duct Connections
4
UNIT SUSPENSION / INSTALLATION
AIR
DISTRIBUTION
BAFFLE
IMPORTANT
To prevent premature heat exchanger failure, observe heat
exchanger tubes by looking at the heat exchanger through
field installed access openings in connecting ductwork. If
the bottom of the tubes become red while blower and duct
furnace are in operation, additional baffles must be inserted
between blower and duct furnace to assure uniform air flow
across the heat exchanger.
C
Airflow Distribution
1. Provide uniform air distribution over the heat exchanger.
Use turning vanes where required (see Figure 5.1) to obtain
uniform air distribution. Avoid installing as in “G”, “H” & “J” of
Figure 5.1.
2. A bottom, horizontal discharge type blower should be
installed at least 12" from the furnace (See “A”, Figure 5.1).
3. A top, horizontal discharge type blower should be installed at
least 24" from the furnace (See “B”, Figure 5.1). Provide air
baffle at top of duct to deflect air down to the bottom of heat
exchanger.

5-564 5
INSTALLATION
Figure 5.1 - Typical Duct & Airflow Installation
RECOMMENCED INSTALLATIONS
Dimensions “B” should never
be less than 1¼2of “A”.
CA
FED
B
12"
Min.
12"
Min.
12"
Min.
12"
Min.
12"
Min.
12"
Min.
24"
Min.
24"
Min.
3" Min.
3" Max.
3" Max.
3" Max.
15° Max. 15° Max.
15° Max.
Air
Baffle
Air
Baffle
Baffle
Baffle
Baffle
B
B
B
BAA
AA
B
Turning
Vanes
Turning
Vanes
Turning
Vanes
Turning
Vanes
Turning
Vanes
3" Min.
Turning
Vanes
3" Max.
3" Min.
Turning
Vanes
SIDE VIEW
SIDE VIEW SIDE VIEW
TOP VIEW
TOP VIEW
TOP VIEW
SIDE VIEW
SIDE VIEW
SIDE VIEW
RECOMMENDED INSTALLATIONS
INSTALLATIONS NOT RECOMMENDED
No Air
No Air No Air
G
POOR
H
POOR
J
POOR
A

65-564
7. Avoid venting through unheated space. When venting does
pass through an unheated space, insulate runs greater than
5 feet to minimize condensation. Inspect for leakage prior to
insulating and use insulation that is noncombustible with a
rating of not less than 350°F. Install a tee fitting at the low
point of the vent system and provide a drip leg with a clean
out cap as shown in Figure 7.1.
NOTE: A vent is the vertical passageway used to convey
flue gases from the unit or the vent connector to the outside
atmosphere. A vent connector is the pipe which connects the
unit to a vent or chimney. Vent connectors serving Category
I appliances shall not be connected into any portion of
mechanical draft systems operating under positive pressure.
Table 6.1 - Vertical Category I Vent Sizing Requirements
WARNING
Table 6.2 - ANSI Venting Requirements
Appliance Venting
Category Description Requirements
INegative vent pressure Follow standard venting
Non-condensing requirements.
II Negative vent pressure Condensate must be
Condensing drained.
III Positive vent pressure Vent must be gastight.
Non-condensing
IV Positive vent pressure Vent must be liquid and
Condensing gastight. Condensate must
be drained.
INSTALLATION
Venting
1. Gas fired heating equipment must be vented - do not
operate unvented.
2. A built-in power exhauster is provided - additional external
power exhausters are not required or permitted.
3. If you are replacing an existing heater, it may be necessary
to resize the venting systems. Improperly sized venting
systems can result in vent gas leakage or the formation of
condensate. Refer to the National Fuel Gas Code ANSI
Z223.1 or CSA B149.1 latest edition. Failure to follow these
instructions can result in injury or death.
4. Under no circumstances should two sections of double wall
vent pipe be joined together within one horizontal vent system
due to the inability to verify complete seal of inner pipes.
Model Size
Vent Connector
Diameter
Minimum Vent Pipe
Diameter
75-125 4" 4"
150-175 4" 5" ➀
200 6" 6"
225-400 6” 6”
➀ Requires a 4" to 5" adapter for the larger vent pipe diameter.
4. For Category I vent systems limit length of horizontal runs to
75% of vertical height. Install with a minimum upward slope
from unit of 1/4 inch per foot and suspend securely from
overhead structure at points no greater than 3 feet apart.
For best venting, put vertical vent as close to the unit as
possible. A minimum of 12" straight pipe is recommended
from the power exhauster outlet before turns in the vent
system. Fasten individual lengths of vent together with at
least three corrosion-resistant sheet-metal screws.
5. It is recommended that vent pipes be fitted with a tee with a
drip leg and a clean out cap to prevent any moisture in the
vent pipe from entering the unit. The drip leg should be inspected
and cleaned out periodically during the heating season.
6. The National Fuel Gas Code requires a minimum clearance
of 6 inches from combustible materials for single wall vent
pipe. The minimum distance from combustible materials is
based on the combustible material surface not exceeding
160°F. Clearance from the vent pipe (or the top of the unit)
may be required to be greater than 6 inches if heat damage
other than fire (such as material distortion or discoloration)
could result.
General Venting Instructions
1. Installation of venting must conform with local building codes,
or in the absence of local codes, with the National Fuel Gas
Code, ANSI Z223.1 (NFPA 54) - Latest Edition. In Canada,
installation must be in accordance with CAN/CGA-B149.1 for
natural gas units and CAN/CGA-B149.2 for propane units.
2. All vertically vented units are Category I. All horizontally vented
units are Category III. The installation must conform to the
requirements from Table 6.2 in addition to those listed below.
3. For units vented as Category I, refer to Table 6.1 for vent
sizing. Vent sizing for units vented as Category III are covered
in a later section on page 7. Do not use a vent pipe smaller
than the size of the outlet or vent transition of the appliance.
The pipe should be suitable corrosion resistant material.
Follow the National Fuel Gas Code for minimum thickness
and composition of vent material. The minimum thickness for
connectors varies depending on the pipe diameter.
8. When the vent passes through a combustible wall or floor,
a metal thimble 4 inches greater than the vent diameter is
necessary. If there is 6 feet or more of vent pipe in the
open space between the appliance and where the vent
pipe passes through the wall or floor, the thimble need only
be 2 inches greater than the diameter of the vent pipe. If a
thimble is not used, all combustible material must be cut
away to provide 6 inches of clearance. Any material used
to close the opening must be noncombustible.
9. Do NOT use dampers or other devices in the vent pipes.
10. Precautions must be taken to prevent degradation of
building materials by flue products.
11. For category I vent systems the outlet of the vent should
extend as shown in Figure 7.1 and Table 7.1 if the following
conditions are met:
• Vent diameter is less than 12 inches, vent is of double
wall construction and is a listed product, and the vent
does not terminate within 2' of a vertical wall or similar
obstruction.
• For vents that have a diameter of 12 inches or larger,
constructed of single wall, or terminate within 2' of a
vertical wall or similar obstruction, the vent pipe shall
extend at least 2' higher than any portion of a building
within a horizontal distance of 10' (refer to Figure 7.1).
12. Use a listed vent terminal to reduce downdrafts and
moisture in vent.
13. For instructions on common venting refer to the National
Fuel Gas Code.
14. The vent must terminate no less than 5' above the vent
connector for Category I vent systems.
15. A unit located within an unoccupied attic or concealed space
shall not be vented with single wall vent pipe.
16. Single wall vent pipe must not pass through any attic, inside
wall, concealed space, or floor.
17. Do NOT vent this appliance into a masonry chimney.
18. When condensation may be a problem, the venting system
shall not terminate over public walkways or over an area
where condensation or vapor could create a nuisance or
hazard or could be detrimental to the operation of regulator
relief openings or other equipment.
19. In cold ambient conditions, such as Canada, the following
items are recommended for proper operation and
equipment life:
• The vent pipe must not pass through an unheated space
or interior part of an open chimney unless the vent pipe is
insulated.
• Where the vent pipe may be exposed to extreme cold, or
come into contact with snow or ice, the entire vent must
be insulated or double wall (includes outdoors). It is
preferred that the double wall vent is one continuous
piece but a joint is allowed outside the building.
• The heater system shall be checked at least once a year
by a qualified service technician.

7
5-564
Additional Requirements for Horizontally Vented
Category III Units
1. Seal the joints with a metallic tape or silastic suitable for
temperatures up to 350°F. (3M tapes 433 or 363 are
acceptable.) Wrap tape two full turns around the vent pipe.
2. Refer to Table 7.2 for total minimum and maximum vent
lengths making the vent system as straight as possible.
The equivalent length of a 90° elbow is 5 feet for 4" diameter
and 7 feet for 6" diameter.
3. The vent terminal must be a Gary Steel 1092.
4. The vent must extend a minimum of 12" beyond the exterior
wall surface as shown in Figure 7.2. The vent must be
supported as shown in Figure 7.3. Precautions must be taken
to prevent degradation of building materials by flue products.
5. The vent system shall terminate at least 3 feet above any
forced air inlet (except direct vent units) located within 10 feet,
and at least 4 feet below, 4 feet horizontally from, or 1 foot
above any door, window, or gravity air inlet into any building.
The bottom of the vent terminal shall be located above the
snow line or at least 1 foot above grade; whichever is greater.
When located adjacent to public walkways the vent system
shall terminate not less than 7 feet above grade.
6. The venting system must be exclusive to a single unit, and
no other unit is allowed to be vented into it.
7. Horizontally vented units must use single wall vent pipe
although one continuous section of double wall vent pipe
may be used with the vent system. Under no circumstances
should two sections of double wall vent pipe be joined
together within one vent system due to the inability to verify
complete seal of inner pipes.
12" MIN
RECOMMENDED
4" MIN
TEE WITH DRIP LEG
AND CLEANOUT CAP
(SLOPE 1/4" PER
FOOT DOWNWARD
TOWARD DRIP LEG)
EXHAUST
"H" MIN*
12" MIN
RECOMMENDED
4" MIN
BACK VIEW
ROOF PITCH IS:
X / 12
TEE WITH DRIP LEG
AND CLEANOUT CAP
(SLOPE 1/4" PER
FOOT DOWNWARD
TOWARD DRIP LEG)
ROOF FLASHING
USE LISTED THIMBLE
THROUGH ROOF AND
CEILING
EXHAUST
12
X
LISTED TERMINAL
* SIZE ACCORNING
TO EXPECTED
SNOW DEPTH.
TO WALL OR ADJOINING BUILDING
2' MIN
2' MIN*
USE THIMBLE
THROUGH
CELLING ROOF FLASHING
TERMINAL
Figure 7.1 - Vertical Category I Vent System
Rise X (in) Roof Pitch Min Height H (ft) ➀
0-6 Flat to 6/12 1.00
6-7 6/12 to 7/12 1.25
7-8 7/12 to 8/12 1.50
8-9 8/12 to 9/12 2.00
9-10 9/12 to 10/12 2.50
10-11 10/12 to 11/12 3.25
11-12 11/12 to 12/12 4.00
12-14 12/12 to 14/12 5.00
14-16 14/12 to 16/12 6.00
16-18 16/12 to 18/12 7.00
18-20 18/12 to 20/12 7.50
20-21 20/12 to 21/12 8.00
Table 7.1 - Minimum Height from Roof to Lowest
Discharge Opening
➀ Size according to expected snow depth.
METAL
SLEEVE
FIBER GLASS
INSULATION
MIN. 2"
2" MIN.
VENT TERMINATION
SUPPORT BRACKET
(where required)
(Make from 1" x 1" steel angle)
9"
9"
45
1"
METAL
SLEEVE
2" MIN.
VENT PIPE
DIAMETER
METAL FACE
PLATE 1"
12" min
Figure 7.3 - Venting Through Combustible Walls
TEE WITH DRIP LEG
AND CLEANOUT CAP
AT LOW POINT OF
VENT SYSTEM
POWER EXHAUSTER OUTLET
PITCH VENT PIPE DOWNWARD
FROM UNIT 1/4" PER FOOT
12"
Min.
GARY STEEL
MODEL 1092 TERMINAL
Figure 7.2 - Horizontal Venting
INSTALLATION
Table 7.2 - Horizontal Category III Vent Sizing
Requirements
Model Size
Vent Connector
Diameter
Minimum Vent
Pipe Diameter
Maxium Vent
Length
75 4" 4" 48'
100-175 4" 4" 55'
200 6" 5" ➀70'
225 6" 6" 70'
250-300 6" 6" 63'
350-400 6" 6" 70'
➀ Unit can be vented with 5" diameter pipe if a 6" to 5" reducer is used.
Otherwise, use 6" pipe.

85-564
Gas Pipe Capacities (Up to 14” W.C. Gas Pressure through Schedule 40 Pipe)
Cubic Feet per Hour with Pressure Drop of 0.3” W.C.
Natural Gas - Specific Gravity - 0.60
Propane Gas - Specific Gravity - 1.50
Length Pipe Diameter
Of Pipe 1/2" 3/4" 1" 1-1/4" 1-1/2" 2"
(feet) Natural Propane Natural Propane Natural Propane Natural Propane Natural Propane Natural Propane
10 132 83 278 175 520 328 1050 662 1600 1008 3050 1922
20 92 58 190 120 350 221 730 460 1100 693 2100 1323
30 73 46 152 96 285 180 590 372 890 561 1650 1040
40 63 40 130 82 245 154 500 315 760 479 1450 914
50 56 35 115 72 215 135 440 277 670 422 1270 800
60 50 32 105 66 195 123 400 252 610 384 1150 725
70 46 29 96 60 180 113 370 233 560 353 1050 662
80 43 27 90 57 170 107 350 221 530 334 990 624
90 40 25 84 53 160 101 320 202 490 309 930 586
100 38 24 79 50 150 95 305 192 460 290 870 548
125 34 21 72 45 130 82 275 173 410 258 780 491
150 31 20 64 40 120 76 250 158 380 239 710 447
Gas Connections
1. Installation of piping must conform with local building codes,
or in the absence of local codes, with the National Fuel Gas
Code, ANSI Z223.1 (NFPA 54) - Latest Edition. In Canada,
installation must be in accordance with CAN/CGA-B149.1 for
natural gas units and CAN/CGA-B149.2 for propane units.
2. Piping to units should conform with local and national
requirements for type and volume of gas handled, and
pressure drop allowed in the line. Refer to Table 10.1 to
determine the cubic feet per hour (cfh) for the type of gas
and size of unit to be installed. Using this cfh value and the
length of pipe necessary, determine the pipe diameter from
Table 8.1. Where several units are served by the same main,
the total capacity, cfh and length of main must be considered.
Avoid pipe sizes smaller than 1/2". Table 8.1 allows for a 0.3"
W.C. pressure drop in the supply pressure from the building
main to the unit. The inlet pressure to the unit must be 6-7"
W.C. for natural gas and 11-14" W.C. for propane gas. When
sizing the inlet gas pipe diameter, make sure that the unit
supply pressure can be met after the 0.3" W.C. has been
subtracted. If the 0.3" W.C. pressure drop is too high, refer to
the Gas Engineer’s Handbook for other gas pipe capacities.
3. The gas piping to the unit can enter the unit from the side of
the unit or from below. Install a ground joint union with brass
seat and a manual shut-off valve external of the unit casing,
and adjacent to the unit for emergency shut-off and easy
servicing of controls, including a 1/8" NPT plugged tapping
accessible for test gauge connection (See Figure 8.1).
4. Provide a sediment trap before each unit in the line where low
spots cannot be avoided. (See Figure 8.1).
5. When Pressure/Leak testing, pressures above 14" W.C. (1/2
psi), close the field installed shut-off valve, disconnect the
appliance and its combination gas control from the gas supply
line, and plug the supply line before testing. When testing
pressures 14" W.C. (1/2 psi) or below, close the manual shut-
off valve on the appliance before testing.
Table 8.1 - Gas Pipe Capacities
WARNING
1. All field gas piping must be pressure/leak tested prior to
operation. Never use an open flame. Use a soap solution or
equivalent for testing.
2. Gas pressure to appliance controls must never exceed 14"
W.C. (1/2 psi).
3. To reduce the opportunity for condensation, the minimum sea
level input to the appliance, as indicated on the serial plate,
must not be less than 5% below the rated input, or 5% below
the minimum rated input of duel rated units.
GAS
SUPPLY LINE
GAS
SUPPLY LINE
GROUND
JOINT
UNION
W/ BRASS
SEAT
MANUAL GAS
SHUT-OFF VALVE
3"
MIN.
SEDIMENT
TRAP
PLUGGED
1/8" NPT TEST
GAGE CONNECTION
TO
CONTROLS
➀
➀ Manual shut-off valve is in the “OFF” position when handle is perpendicular to
pipe.
IMPORTANT
To prevent premature heat exchanger failure, the input to the
appliance, as indicated on the serial plate, must not exceed
the rated input by more than 5%.
CAUTION
Purging of air from gas lines should be performed as
described in ANSI Z223.1 - latest edition “National Fuel Gas
Code”, or in Canada in CAN/CGA-B149 codes.
INSTALLATION
Figure 8.1 - Recommended Sediment Trap/Manual
Shut-off Valve Installation - Side or Bottom Gas
Connection

9
5-564
Electrical Connections
1. Installation of wiring must conform with local building codes,
or in the absence of local codes, with the National Electric
Code ANSI/NFPA 70 - Latest Edition. Unit must be electrically
grounded in conformance to this code. In Canada, wiring
must comply with CSA C22.1, Part 1, Electrical Code.
2. All duct furnaces are provided with a wiring diagram located
on the inside door of the electrical junction box. Refer to this
wiring diagram for all wiring connections. For factory installed
options and field installed accessory wiring, refer to Set A and
Set B on the provided wiring diagram.
3. The power supply to the duct furnace should be protected
with a fused disconnect switch.
4. Refer to Table 9.1 to determine the amp draw of the duct
furnace by adding the amp draw for the control transformer
(includes ignition controllers, gas valves, control relays, and
amplifiers) and power exhauster together, based on the
voltage and model size. Size the disconnect switch to cover
the amp draw of the unit.
5. Refer to the unit dimensional drawing on page 15 for the
electrical knockout locations.
START-UP PROCEDURE
1. Turn off power to the unit at the disconnect switch. Check
that fuses or circuit breakers are in place and sized
correctly. Turn all hand gas valves to the “OFF” position.
2. Check that the supply voltage matches the unit supply
voltage listed on the serial plate. Verify that all wiring is
secure and properly protected. Trace circuits to insure that
the unit has been wired according to the wiring diagram.
3. Check to insure that the venting system is installed and free
from obstructions.
4. Check to see that there are no obstructions to the intake
and discharge of the duct furnace.
5. Perform a visual inspection of the unit to make sure no
damage has occurred during installation.
6. Turn on power to the unit at the disconnect switch. Check to
insure that the voltage between terminals 1 and 2 is 24V.
7. Check the thermostat, ignition control, gas valve, power
exhauster motor, and supply fan blower motor for electrical
operation. If these do not function, recheck the wiring
diagram. Check to insure that none of the Gas Control
Options & Accessories (see page 14) have tripped.
8. Recheck the gas supply pressure at the field installed
manual-shut-off valve. The inlet pressure should be 6"-7”
W.C. on natural gas and 11"-14” W.C. on propane gas.
If inlet pressure is too high, install an additional pressure
regulator upstream of the combination gas control.
9. Open the field installed manual gas shut-off valve.
10. Open the manual main gas valve on the combination gas
control. Call for heat with the thermostat. On a call for heat,
the power exhauster relay will energize the power exhauster
motor. Once the power exhauster motor has reached full
speed, the differential pressure switch will close. Once
closed, the ignition controller will attempt to light the pilot.
If the pilot does not light, purge the pilot line. If air purging
is required, disconnect the pilot line at outlet of pilot valve.
In no case should the line be purged into heat exchanger.
Check the pilot flame length (See Pilot Burner Adjustment).
11. Once the pilot has been established, check to make sure
that the main gas valve opens. Check the manifold gas
pressure (See Main Burner Adjustment) and flame length
(See Air Shutter Adjustment) while the circulating air blower
is operating.
12. Check to insure that gas controls sequence properly
(See Control Operating Sequence). Verify if the unit has
any additional control devices and set according to the
instructions in the Gas Controls Options.
13. Once proper operation of the duct furnace has been
verified, remove any jumper wires that were required for
testing.
14. Close the electrical compartment door.
WARNING
1. Disconnect power supply before making wiring connections
to prevent electrical shock and equipment damage.
2. All appliances must be wired strictly in accordance with
wiring diagram furnished with the appliance. Any wiring
different from the wiring diagram could result in a hazard
to persons and property.
3. Any original factory wiring that requires replacement must
be replaced with wiring material having a temperature
rating of at least 105°C.
4. Ensure that the supply voltage to the appliance, as indicated
on the serial plate, is not 5% greater than rated voltage.
INSTALLATION / START-UP PROCEDURE
IMPORTANT
Start-up and adjustment procedures should be performed by a
qualified service agency.
➀Unit controls amp draw is included in master unit amp draw.
➁Requires a 250 VA transformer.
➂ Requires a 500 VA transformer.
➃ For Digits F (460V) and G (575V), amp draw shown is on primary (line) side of
required step-down transformer.
CAUTION
Ensure that the supply voltage to the appliance, as indicated
on the serial plate, is not 5% less than rated voltage.
Digit 14 Control Step Down
Transformer Amp Draw
Power Exhauster
Amp Draw
Supply Voltage Digit 15 - Transformer Model Size
0 ➀1 2 3 4 75-175 200-400
A115/60/1 0 0.35 0.65 1.3 2.17 1.4 2.4
B 208/60/1 0 0.19 0.36 0.72 1.2 0.7 1.4
C 230/60/1 0 0.17 0.33 0.65 1.09 0.6 1.3
D 208/60/3 0 0.19 0.36 0.72 1.2 0.7 1.4
E 230/60/3 0 0.17 0.33 0.65 1.09 0.6 1.3
F 460/60/3 ➃0 0.09 0.16 0.33 0.54 0.30 ➁0.65 ➂
G575/60/3 ➃0 0.07 0.13 0.26 0.43 0.24 ➁0.52 ➂
Table 9.1 - Unit Amps

10 5-564
Pilot Burner Adjustment
The pilot burner is orificed to burn properly with an inlet pressure
of 6-7" W.C. on natural gas and 11-14" W.C. on propane gas, but
final adjustment must be made after installation. If the pilot flame
is too long or large, it is possible that it may cause soot and/or
impinge on the heat exchanger causing failure. If the pilot flame
is shorter than shown, it may cause poor ignition and result in
the controls not opening the combination gas control. A short
flame can be caused by a dirty pilot orifice. Pilot flame condition
should be observed periodically to assure trouble-free operation.
To Adjust the Pilot Flame
1. Create a call for heat from the thermostat.
2. Remove the cap from the pilot adjustment screw. For location,
see the combination gas control literature supplied with unit.
3. Adjust the pilot length by turning the screw in or out to achieve
a soft steady flame 3/4" to 1" long and encompassing 3/8"-
1/2" of the tip of the thermocouple or flame sensing rod (See
Figure 10.1).
4. Replace the cap from the pilot adjustment screw.
Figure 10.1 - Correct Pilot Flame
Main Burner Adjustment
The gas pressure regulator (integral to the combination gas
control) is adjusted at the factory for average gas conditions. It is
important that gas be supplied to the duct furnace in accordance
with the input rating on the serial plate. Actual input should
be checked and necessary adjustments made after the duct
furnace is installed. Over-firing, a result of too high an input,
reduces the life of the appliance and increases maintenance.
Under no circumstances should the input exceed that shown on
the serial plate.
Measuring the manifold pressure is done at the tee in the
manifold for premium gas controls (Digit 13=0, 1, 2, or 3) or
at the pressure tap on the gas valve for standard gas controls
(Digit 13=4)." (See Figure 10.2).
START-UP PROCEDURE
3/4" to 1"
To Adjust the Manifold Pressure
1. Move the field installed manual shut-off valve to the “OFF”
position.
2. Remove the 1/8" pipe plug in the pipe tee or gas valve and
attach a water manometer of “U” tube type which is at least
12" high.
3. Move the field installed manual gas shut-off valve to the “ON”
position.
4. Create a high fire call for heat from the thermostat.
5. Determine the correct high fire manifold pressure. For
natural gas 3.5” W.C., for propane gas 10” W.C. Adjust the
main gas pressure regulator spring to achieve the proper
manifold pressure (for location, see the combination gas
control literature supplied with unit).
6. If the unit has Electronic Modulation gas controls (determine
from the Model Identification Digit 12), the low fire gas
pressure needs to be adjusted. Using Figure 10.3 for item
number locations, this is accomplished as follows:
a. Disconnect power.
b. Remove all wires from Maxitrol Amplifier terminal “3” or
duct furnace terminal “43” (if available).
c. Turn on power at the disconnect switch.
d. Remove the maximum adjustment screw (4), spring
(5), and plunger (8). A small magnet is useful for this
purpose. CAUTION - The plunger is a precision part.
Handle carefully to avoid marring or picking up grease
and dirt. Do not lubricate.
e. Using minimum adjusting screw (9), adjust low fire
manifold pressure to 0.56" W.C. for natural gas and
1.6" W.C. for propane gas.
f. Replace plunger and spring retainer, spring, and
maximum adjusting screw in proper order.
g. Using maximum adjustment screw (4), adjust high fire
manifold pressure to 3.5" W.C. for natural gas and 10"
W.C. for propane gas.
h. Disconnect power.
i. Replace cover plate (2) and re-install all wires from
Maxitrol amplifier terminal “3” or duct furnace terminal “43”.
7. After adjustment, move the field installed manual shut-off
valve to the “OFF” position and replace the 1/8" pipe plug.
8. After the plug is in place, move the field installed manual
shut-off valve to the “ON” position and recheck pipe plugs for
gas leaks with soap solution.
Figure 10.3 - Maxitrol Modulating Valve Adjustments
1. TOP HOUSING
2. COVER PLATE
3. SEAL GASKET
4. MAXIMUM ADJUSTMENT SCREW
5. MAXIMUM ADJUSTMENT SPRING
6. SOLENOID
7. MINIMUM ADJUSTMENT SPRING
8. PLUNGER
9. MINIMUM ADJUSTMENT SCREW
10. MINIMUM ADJUSTMENT SCREW STOP
Figure 10.2 - Manifold Pressure Test Points
Standard Controls
Premium Controls
Manifold Pressure Test Point

11
5-564
Air Shutter Adjustment
Proper operation provides a soft blue flame with a well-defined
inner core. A lack of primary air will reveal soft yellow-tipped
flames. Excess primary air produces short, well-defined flames
with a tendency to lift off the burner ports. For both natural
and propane gas, the air shutters can be adjusted to control
the burner flame height. The air shutters can be accessed by
reaching behind the gas valve in Figure 10.3. The larger models
may require the removal of the manifold (see Manifold Assembly
Removal).
Natural Gas Flame Control
Control of burner flames on duct furnaces utilizing natural gas
is achieved by resetting the primary air shutters (See Figure
19.1) to either increase or decrease primary combustion air.
Prior to flame adjustment, operate duct furnace for about fifteen
minutes. The main burner flame can be viewed after loosening
and pushing aside the gas designation disc on the side of the
burner box.
To increase primary air, loosen the air shutter set screws and
move the air shutters closer to the manifold until the yellow-
tipped flames disappear. (See Figure 19.1 for air shutter and
heat exchanger support locations.) To decrease primary air,
move the air shutters away from the manifolds until flames
no longer lift from burner ports, but being careful not to cause
yellow tipping. Retighten set screws after adjustment.
Propane Gas Flame Control
An optimum flame will show a slight yellow tip. Prior to flame
adjustment, operate furnace for at least fifteen minutes. Loosen
air shutter set screws and move the air shutters away from the
manifold to reduce the primary air until the yellow flame tips
appear. Then increase the primary air until yellow tips diminish
and a clean blue flame with a well defined inner cone appears.
Model Size Type of Gas Natural Propane
Btu/Cu. Ft. 1040 2500
Specific Gravity 0.60 1.53
High Fire Manifold Pressure No. of
Inches of Water Column 3.5 10 Orifices
Cfh 72.1 30.0 1
Orifice Drill Size 20 37
Cfh 96.1 40.0 2
Orifice Drill Size 30 45
Cfh 120.2 50.0 2
Orifice Drill Size 25 42
Cfh 144.2 60.0 3
Orifice Drill Size 30 45
Cfh 168.3 70.0 3
Orifice Drill Size 27 43
Cfh 192.3 80.0 3
Orifice Drill Size 23 40
Cfh 216.3 90.0 3
Orifice Drill Size 20 37
Cfh 240.4 100.0 4
Orifice Drill Size 25 42
Cfh 288.7 120.0 4
Orifice Drill Size 20 37
Cfh 336.5 140.0 6
Orifice Drill Size 27 43
Cfh 384.6 160.0 6
Orifice Drill Size 23 40
START-UP PROCEDURE
100
125
150
175
400
75
350
300
250
225
200
Table 11.1 - Manifold Pressure and Gas Consumption

12 5-564
START-UP PROCEDURE
Control Operating Sequence
Indoor power vented duct furnaces are supplied with intermittent
pilot systems with continuous retry as standard. On mechanical
modulation systems the main burner is turned off 100%
when the thermostat is satisified, but the pilot remains lit. For
intermittent pilot systems, except mechanical modulation both
the main burner and pilot burner are turned off 100% when
the thermostat is satisfied. Intermittent pilot systems, for both
natural and propane gas, the ignition controller is 100% shut-off
with continuous retry. On a call for heat, the system will attempt
to light the pilot for 70 seconds. If the pilot is not sensed for
any reason, the ignition control will wait for approximately six
minutes with the combination gas control closed and no spark.
After six minutes, the cycle will begin again. After three cycles,
some ignition controllers lockout for approximately one hour
before the cycle begins again. This will continue indefinitely until
the pilot flame is sensed or power is interrupted to the system.
NOTE: Gas Control Options (see page 14) could change the
listed sequence of operation based on their function.
The descriptions given are for the basic duct furnace.
Single-Stage Gas Controls
Utilizes a single-stage combination gas, an ignition control, and
a single-stage low voltage thermostat.
1. The thermostat calls for heat.
2. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed, the
differential pressure switch closes. The power exhauster relay
pre-purge timer closes after 20 to 40 seconds energizing the
gas control circuit.
3. The pilot valve opens and the spark ignitor sparks in an
attempt to light the pilot. (If the unit was not provided with a
time delay relay, the blower starts at this time.)
4. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark ignitor from sparking.
5. The main gas valve is opened and the main burner is lit to
100% full fire.
6. If the unit was provided with a time delay relay, the blower
starts after 30 to 45 seconds.
7. The unit continues to operate until the thermostat is satisfied,
at which time both the main and pilot valves close 100%. (If
the unit was not provided with a time delay relay, the blower
stops at this time).
8. If the unit was provided with a time delay relay, the blower
stops after 30 to 45 seconds.
Two-Stage Gas Controls
Utilizes a two-stage combination gas control, an ignition control,
and a two-stage low voltage thermostat. The unit fires at 50%
fire on low stage and 100% fire on high stage.
1. The thermostat calls for low stage heat.
2. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed, the
differential pressure switch closes. The power exhauster relay
pre-purge timer closes after 20 to 40 seconds energizing the
gas control circuit.
3. The pilot valve opens and the spark ignitor sparks in an
attempt to light the pilot. (If the unit was not provided with a
IMPORTANT
To prevent premature heat exchanger failure, with all control
systems, a blower starting mechanism must be provided so
that the blower is running or energized within 45 seconds of
the gas control operation.
time delay relay, the blower starts at this time.)
4. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark ignitor from sparking.
5. The main gas valve is opened and the main burner is lit to
50% fire.
6. If the unit was provided with a time delay relay, the blower
starts after 30 to 45 seconds.
7. If the temperature at the thermostat continues to fall, the
thermostat will call for high stage heat.
8. The main gas valve is opened completely and the main
burner is lit to 100% full fire.
9. The unit continues to operate until the high stage of the
thermostat is satisfied, at which time the main valve closes
to 50% fire.
10. The unit continues to operate until the low stage thermostat
is satisfied, at which time both the main and pilot valves
close 100%. (If the unit was not provided with a time delay
relay, the blower stops at this time.)
11. If the unit was provided with a time delay relay, the blower
stops after 30 to 45 seconds.
Utilizes a mechanical modulating gas control and an ignition
control. The mechanical modulating gas control is designed
for use in constant blower applications. The discharge air
temperature is maintained by setting the control dial of the
modulating gas valve in one of ten positions. A hydrostatic
sensing bulb located in the discharge air stream controls the gas
flow between 40% through 100% full fire. When the discharge
air hydrostatic sensing bulb is satisfied, the modulating valve
closes completely, but the pilot remains lit.
This control cannot be used with a room override thermostat.
1. Power is supplied to the unit through either an exhaust fan
interlock contact or a start/stop switch.
2. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed, the
differential pressure switch closes. The power exhauster relay
pre-purge timer closes after 20 to 40 seconds energizing the
gas control circuit.
3. The pilot valve opens and the spark ignitor sparks in an
attempt to light the pilot. (If the unit was not provided with a
time delay relay, the blower starts at this time.)
4. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark ignitor from sparking.
5. The hydrostatic sensing bulb, integral to the mechanical
modulating gas valve, calls for heat. The main gas valve is
opened and the main burner is lit. The burner modulates
between 40% through 100% fire based on the call for heat.
6. If the unit was provided with a time delay relay, the blower
starts after 30 to 45 seconds.
7. The unit continues to operate until the hydrostatic sensing
bulb is satisfied, at which time the main valve closes 100%,
but the pilot remains lit.
8. The unit blower (and pilot) continues to operate until either an
exhaust fan interlock contact or a start/stop switch is opened.
If the unit was provided with a time delay relay, the blower
stops after 30 to 45 seconds.
Dial Number
Lo 1 2 3 4 5 6 7 8 Hi
Discharge
Air Temp. 58 62 65 69 72 76 79 83 86 90
(°F)
Mechanical Modulating Gas Controls (Natural Gas Only)

13
5-564
Electronic Modulating Gas Controls
Single Furnace
Utilizes an electronic modulating/regulating gas control,
combination gas valve, an ignition control, modulating amplifier,
and either a modulating room thermostat or modulating duct
thermostat with remote temperature set point adjuster. The
thermostat controls can modulate the gas flow between 40%
through 100% full fire. When the thermostat is satisfied, the amplifier
cuts power to the combination gas valve which prevents gas
flow to both the main and pilot burners.
When duct sensing is utilized, a room override thermostat can
be added. When calling for heat, the room override thermostat
provides full fire operation until the space temperature is
satisfied. Control is then returned to the duct sensing control.
In this situation, either the duct sensor or the room override
thermostat can call for heat.
1. The thermostat calls for heat.
2. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed, the
differential pressure switch closes. The power exhauster relay
pre-purge timer closes after 20 to 40 seconds energizing the
gas control circuit.
3. The pilot valve opens and the spark ignitor sparks in an
attempt to light the pilot. (If the unit was not provided with a
time delay relay, the blower starts at this time.)
4. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark ignitor from sparking.
5. The main gas valve is opened and the main burner is lit to
100% full fire.
6. If the unit was provided with a time delay relay, the blower
starts after 30 to 45 seconds.
7. The modulating gas valve can be controlled by either an
electronic modulating room or duct thermostat. The thermostat
can modulate the firing rate between 40% through 100% full fire.
The call for heat is created by a resistance signal (8000 to 12000
ohms) in the thermostat. The amplifier converts this resistance
into a DC voltage (0 to 12 volts DC with 0 volts high fire and 12
volts low fire). The output voltage is applied to the modulating
gas valve to control the gas flow to the main burner. As the
temperature drops, the voltage drops causing the modulating
valve to open further. If the discharge air temperature increases,
the voltage increases causing the modulating valve to close
allowing less gas flow to the main burner. For further information
regarding the operation of the electronic modulating system,
consult the literature provided with the unit.
8. The unit continues to operate in this manner until the
thermostat is satisfied, at which time both the main and pilot
valves close 100%. (If the unit was not provided with a time
delay relay, the blower stops at this time.)
9. If the unit was provided with a time delay relay, the blower
stops after 30 to 45 seconds.
Electronic Modulating Gas Controls - Master/Slave
One Master furnace is provided with up to three Slave furnaces
that utilize electronic modulating/regulating gas controls,
combination gas valves, ignition controls, one multiple furnace
modulating amplifier, and either a modulating room thermostat
or modulating duct thermostat with remote temperature adjuster.
The thermostat controls can modulate the gas flow of all the
furnaces between 40% through 100% full fire. The amplifier
sends a signal to all of the gas valves so that they modulate
at the same percentage. When the thermostat is satisfied,
the amplifier cuts power to the combination gas valves which
prevents gas flow to both the main and pilot burners.
When duct sensing is utilized, a room override thermostat can
be added. When calling for heat, the room override thermostat
provides full fire operation until the space temperature is
satisfied. Control is then returned to the duct sensing control.
In this situation, either the duct sensor or the room override
thermostat can call for heat.
START-UP PROCEDURE
The sequence of operation for Electronic Modulating Gas
Controls - Master/Slave is the same as Electronic Modulating
Gas Controls - Single Furnace.
Electronic Modulating Gas Controls - Building
Management Control (0-10Vdc or 4-20 mA Signal)
Utilizes an electronic modulating/regulating gas control,
combination gas valve, an ignition control, modulating signal
conditioner, and an inverted (0 Vdc or 4 mA being high fire and
10 Vdc or 20 mA being low fire) 0-10 Vdc or 4-20 mA input
signal provided by a Building Management System (BMS). The
signal conditioner can modulate the gas flow between 40%
through 100% full fire. When the BMS thermostat (field supplied)
is satisfied, the BMS heat contact (field supplied) opens to cut
power to the combination gas valve which prevents gas flow to
both the main and pilot burners.
1. The BMS thermostat (field supplied) calls for heat and closes
the BMS heat contact (field supplied).
2. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed, the
differential pressure switch closes. The power exhauster relay
pre-purge timer closes after 20 to 40 seconds energizing the
gas control circuit.
3. The pilot valve opens and the spark ignitor sparks in an
attempt to light the pilot. (If the unit was not provided with a
time delay relay, the blower starts at this time.)
4. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark ignitor from sparking.
5. The main gas valve is opened and the main burner is lit to
100% full fire.
6. If the unit was provided with a time delay relay, the blower
starts after 30 to 45 seconds.
7. The modulating gas valve is controlled by the BMS
thermostat. The thermostat can modulate the firing rate
between 40% through 100% full fire by modulating the input
signal between either 0-10 Vdc or 4-20 mA (The signal
conditioner can accept a 0-10 Vdc signal when all the dip
switches are in the “OFF” position and 4-20 mA signal when
all the dip switches are in the “ON” position). The signal
conditioner converts the input signal into a DC voltage (0
to 12 volts DC with 0 volts high fire and 12 volts low fire).
The output voltage is applied to the modulating gas valve to
control the gas flow to the main burner. As the temperature
drops, the voltage drops causing the modulating valve to open
further. If the discharge air temperature increases, the voltage
increases causing the modulating valve to close allowing less
gas flow to the main burner. For further information regarding
the operation of the electronic modulating system, consult the
literature provided with the unit.
8. The unit continues to operate in this manner until the
thermostat is satisfied, at which time the BMS heat contact
opens resulting in both the main and pilot valves closing
100%. (If the unit was not provided with a time delay relay, the
blower stops at this time.)
9. If the unit was provided with a time delay relay, the blower
stops after 30 to 45 seconds.
Variable Air Movement Applications
When the air mover supplied by others can provide variable
air movement (i.e. 2-speed or variable frequency drive units),
the allowable minimum CFM of the duct furnace can be 66% of
the minimum listed CFM in Table 16.1 if the unit is applied as
follows:
1. The unit is provided with 2-stage, mechanical modulation, or
electronic modulating gas controls. (see Model Identification).
2. The unit is provided with a factory installed discharge air
controller.
3. The system does not include a room thermostat.
The factory installed discharge air thermostat will prevent the
unit from firing above the allowable 100°F rise when the unit is
at or above the minimum CFM by monitoring the discharge air
and going to low fire. A room thermostat, because it is located
remote from the unit, could cause the unit to over-fire.

14 5-564
➅Air Flow Proving Switch
The air flow proving switch is factory installed in the duct furnace
electrical junction box. The air flow proving switch monitors the
pressure differential between the duct furnace and the atmosphere.
The purpose of the air flow proving switch is to cut power to the
gas controls if a positive pressure is not measured by the switch.
This could be caused by a lack of air movement through the heat
exchanger.
NOTE: The air flow proving switch will prevent any heat
exchanger warm-up (the unit should not be equipped with
a time delay relay) because the gas controls can not be
energized until air flow is proven.
Setting the Air Flow Proving Switch
The range of the air flow proving switch is adjustable between 0.17"
to 5.0" W.C.
1. Set the thermostat so that there is a call for heat. This should fire
the burner and the blower should start.
2. Turn the set screw of the pressure switch clockwise until it stops.
This will set the pressure at 5.0" W.C.
3. Turn the screw counter-clockwise until the gas controls light and
then one additional full turn (This is approximately 0.25'' W.C.).
This will allow for dirty filters or any other slight static pressure
increases in the system.
➆Manual Reset High Limit
The manual reset high limit switch is factory installed in place
of the standard automatic reset high limit switch located in the
duct furnace electrical junction box. In case of a failure of the
blower motor, blockage of the inlet air, etc., the manual reset
switch prevents the unit from cycling on the high limit. If the limit
temperature is exceeded, a service person must inspect the unit for
the cause of the high discharge temperature, take corrective action,
and then reset the switch.
Figure 14.1 - Location of Gas Control Options
Gas Control Options
The unit must be reviewed to determine if any of the listed gas
control options were supplied.
➀Time Delay Relay
The Time Delay Relay is factory installed in the duct furnace
electrical junction box. The standard duct furnace is provided
for instantaneous fan operation. On a call for heat, the blower is
energized at the same time as the gas controls. The optional time
delay relay allows the gas controls to operate for approximately 30
seconds before the blower starts. This allows the heat exchanger
a warm up period so that the initial delivered air coming out of the
ductwork is not cool. The time delay relay also keeps the motor
running for approximately 30 seconds after the call for heat has
been satisfied to remove the residual heat from the heat exchanger.
➁Low Gas Pressure Switch
The low gas pressure switch is factory installed in the duct furnace
above the gas train. The switch monitors the gas pressure upstream
of all the gas controls and shuts off the electric supply to the
ignition controller and combination gas valve if low gas pressure is
experienced. This will shut off all gas flow to the burner. The switch
has an automatic reset so that if the gas pressure is interrupted
and then is returned, the switch will automatically allow the unit to
operate when gas conditions are returned to the allowable range
of the pressure switch. The pressure switch range is 2" to 14" W.C.
and should be set to insure that the minimum inlet gas pressure is
available (6" W.C. for natural gas, 11" W.C. for propane gas).
➂High Gas Pressure Switch
The high gas pressure switch is factory installed in the duct
furnace above the gas train. The switch monitors the gas pressure
downstream of all the gas controls and shuts off the electric supply
to the ignition controller and combination gas valve if high gas
pressure is experienced right before the manifold. This will shut off
all gas flow to the burner. The switch has a manual reset so that if
the gas pressure is too high, a service person must check the unit
to make sure that none of the gas controls have been damaged
by the high gas pressure and then reset the switch to allow the
unit to operate when gas conditions are returned to the allowable
range of the pressure switch. The pressure switch range is 2" to 16"
W.C. and should be set to insure that the maximum manifold gas
pressure is not exceeded (3.5" W.C. for natural gas, 10" W.C. for
propane gas).
➃Supply Air Fire Stat
The fire stat is factory installed in the duct furnace electrical junction
box with the sensor in the discharge air stream. In case of elevated
temperatures in the supply air, the manual reset switch shuts
down the entire unit. If the limit temperature is exceeded, a service
person must inspect the unit for the cause of the high discharge
temperature, take corrective action, and then reset the switch.
➄Timed Freeze Protection
The timed freeze protection system is factory installed in the duct
furnace electrical junction box with the sensor (30°-75°F adjustable)
factory installed in discharge air stream. On initial start-up, the
timed delay in the system allows the unit to go through the normal
ignition sequence. The timed delay is an automatic reset switch and
adjustable for 1-10 minutes. In the event that the unit fails to fire
after this period, the discharge air sensor will sense the cold air and
will shut down the entire unit.
OPTIONS
Units with Standard
Control Panel
Units with Premium Control Box
13
48
6
46
6
8
57
9
13
49
2
3
50
5
4
1
10
9
8
12
46
47
55
51
52
12
300
FM
R
LISTED
PRESSURE
OPERATED
SWITCH
504H
ADDISON
IL.U.S.A.
MODEL
RLGP-A
M1
LOW
PRESSURE
50
100
150
200
350
250
mm.
W.C.
2
4
6
8
10
14
IN.
12
300
FM
R
LISTED
PRESSURE
OPERATED
SWITCH
504H
ADDISON
IL.U.S.A.
MODEL
RLGP-A
M1
LOW
PRESSURE
50
100
150
200
350
250
mm.
W.C.
2
4
6
8
10
14
IN.
123456
A1010 Amplifier
89101114
GH
T
PV
MV
LED
TH
PV/MV
GND
TR
SENSE
1. Discharge Thermostat
2. Low Gas Pressure Switch
3. High Gas Pressure Switch
4. Power Exhauster
5. Timed Freeze Protection
6. Ignition Controller
8. Control Relay
9. Time Delay Relay
10. Furnace Low Voltage Terminal Strip
12. Furnace Supply Power Terminal Strip
Note: Wrap around gas train on
premium and electronic
modulation units only.
13. Control Step Down Transformer
46. Electronic Modulating Amplifier
47. Electronic Modulating Gas Valve
48. Air Flow Proving Switch
49. High Limit Switch
50. Supply Air Fire Stat
51. Main Gas Valve
52. Burner Box
55. Differential Pressure Switch
57. Control Terminal Board

15
5-564
DIMENSIONAL DATA
Table 15.1 - Indoor Power Vented Duct Furnace Dimensions
(All Dimensions in inches) Model Size
Dimensions 75 100/125 150/175 200/225 250/300 350/400
A 15.41 17.90 22.16 24.29 27.33 38.83
B 33.05 33.05 33.05 37.05 37.05 37.05
C (standard) 22.43 22.43 22.43 24.09 24.09 24.09
D 15.21 17.70 21.96 24.09 27.13 38.63
E 19.07 19.07 19.07 23.07 23.07 23.07
F 14.09 16.59 20.85 22.98 26.01 37.51
G 12.65 15.14 19.41 21.60 24.60 36.14
H 23.75 26.26 30.51 32.78 35.79 47.32
I 17.83 17.83 17.83 20.68 20.68 20.68
J 4 4 4 6 6 6
K 14.55 17.04 21.31 23.26 26.44 37.80
M 2.01 2.01 2.01 1.94 1.94 1.94
N 29.65 29.65 29.65 33.65 33.65 33.65
O (max. approx.) (standard) 5.6 5.6 5.6 6.8/6.2 6.2 8.3/8.6
P14.03 14.03 14.03 17.40 17.40 17.40
Gas Connection Pipe Size (max. std.) 1/2 1/2 1/2 1/2 / 3/4 3/4 3/4
Gas Connection Pipe Size (max. prem.) 3/4 3/4 3/4 3/4 3/4 3/4
Approx. Unit Shipping 101# 125# 152# 187# 225# 296#
Weight Unit Net 85# 107# 133# 167# 193# 263#
PREMIUM
CONTROL
BOX
K
N B
F (MOUNTING HOLES)
G
D (DUCT SIZE)
A
H
O
M
I
C
8.965 10.50
E (DUCT SIZE)
P
J (ROUND)
18.39
(MOUNTING
HOLES)
22.907
1.41
Figure 15.1 - Indoor Power Vented Duct Furnace Dimensions

16 5-564
Air Temperature Rise Through Unit (°F)
Model Btu/Hr 20
➂ 40 ➂ 50 ➂ 60 65 70 75 80 85 90 95 100 ➃
Size Input Output Max Min
75 75,000 60,000 2778 1389 1111 926 855 794 741 694 654 617 585 556
100 100,000 80,000 3704 1852 1481 1235 1140 1058 988 926 871 823 780 741
125 125,000 100,000 4630 2315 1852 1543 1425 1323 1235 1157 1089 1029 975 926
150 150,000 120,000 5556 2778 2222 1852 1709 1587 1481 1389 1307 1235 1170 1111
175 175,000 140,000 6481 3241 2593 2160 1994 1852 1728 1620 1525 1440 1365 1296
200 200,000 160,000 7407 3704 2963 2469 2279 2116 1975 1852 1743 1646 1559 1481
225 225,000 180,000 8333 4167 3333 2778 2564 2381 2222 2083 1961 1852 1754 1667
250 250,000 200,000 9259 4630 3704 3086 2849 2646 2469 2315 2179 2058 1949 1852
300 300,000 240,000 11111 5556 4444 3704 3419 3175 2963 2778 2614 2469 2339 2222
350 350,000 280,000 11111➄6481 5185 4321 3989 3704 3457 3241 3050 2881 2729 2593
400 400,000 320,000 11111➄7407 5926 4938 4558 4233 3951 3704 3486 3292 3119 2963
PERFORMANCE
➀ Ratings are shown for elevations up to 2000 feet. For higher elevations, the input rating should be reduced at the rate of 4% per 1000 feet elevation above sea level. For Canada, in
elevations between 2000 and 4500 feet, the unit must be derated to 90% of the rating listed above.
➁ Units approved for use in California by CEC.
➂ Power vented indoor duct furnaces are supplied with a factory installed air baffle. For applications where an air tempature rise less than 60°F is desired, it is recomended to remove
this baffle to reduce system pressure drop.
➃ For Variable Air Movement Applications, see page 13.
➄ The maximum CFM for the 350 and 400 results in a 23°F and a 27°F air temperature rise (respectively) based on the maximum unit pressure drop.
Air Temperature and External Static Pressure Limits
The maximum allowable discharge air temperature is 150°F. The maximum allowable air temperature rise for all Power Vented Units
is 100°F. All duct furnaces are designed for a maximum allowable static pressure of 3.0" W.C. on the heat exchanger.
Figure 16.1 - Recommended Unit Configurations
200,000
BTU/HR
OUTPUT 65°F
TEMP. RISE
160,000
BTU/HR
OUTPUT
65°F
TEMP. RISE
160,000
BTU/HR
OUTPUT
65°F
TEMP. RISE
160,000
BTU/HR
OUTPUT
65°F
TEMP. RISE
TANDEM TOP VIEW
SINGLE TOP VIEW PARALLEL TOP VIEW
2279 CFM
60°F ENTERING
AIR TEMP.
2279 CFM
20°F ENTERING
AIR TEMP.
125°F DISCHARGE
AIR TEMP.
150°F DISCHARGE
AIR TEMP.
5698 CFM
20°F ENTERING
AIR TEMP.
PREHEAT
UNIT
REHEAT
UNIT
200,000
BTU/HR
OUTPUT 65°F
TEMP. RISE
85°F DISCHARGE
AIR TEMP.
SEE SERVICE
CLEARANCES
Table 16.1 - Air Temperature Rise - Power Vented Indoor Duct Furnaces ➀ ➁
CFM

17
5-564
PRESSURE DROP CURVES
Figure 17.1 - Indoor Duct Furnace Without Baffle Pressure Drop vs CFM curves
0
0.2
0.4
0.6
0.8
1
1.2
1.4
01000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000
CFM
PRESSURE DROP
(ΔP " W.C.)
75
100/125
150/175
200/225
250/300
350/400
Caution:
Do not exceed the CFM ranges
indicated in Table 16.1
Figure 17.2 - Indoor Duct Furnace With Baffle Pressure Drop vs CFM curves
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
01000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000
CFM
PRESSURE DROP
( ΔP " W.C.)
75
100/125
150/175
Caution:
Do not exceed the CFM ranges
indicated in Table 16.1
200/225
250/300 350/400

18 5-564
Duct Furnace
When providing annual maintenance for the duct furnace, keep
the unit free from dust, dirt, grease and foreign matter. Pay
particular attention to:
1. The exhaust vent piping and vent terminal.
2. The burner ports and pilot burner orifices (avoid the use of
hard, sharp instruments capable of damaging surfaces for
cleaning these ports). To check the burner port and pilot
burner orifice, see Burner and Pilot Assembly Removal.
3. The air shutters and main burner orifices (avoid the use of
hard, sharp instruments capable of damaging surfaces for
cleaning these orifices). To check the air shutters and main
burner orifices, see for Manifold Assembly Removal.
The heat exchanger should be checked annually for cracks
and discoloration of the tubes. If a crack is detected, the heat
exchanger should be replaced before the unit is put back into
service. If the tubes are dark gray, airflow across the heat
exchanger should be checked to insure that a blockage has not
occurred or the blower is operating properly.
Power Exhauster Motor
The power exhaust motor bearings have been lubricated
for long life and do not require additional lubrication. In dirty
atmosphere, it may be desirable to clean the motors and blower
housing and blow out the cooling air passages of the motor with
compressed air.
Electrical Wiring
The electrical wiring should be checked annually for loose
connections or deteriorated insulation.
Gas Piping & Controls
The gas valves and piping should be checked annually for
general cleanliness and tightness.
The gas controls should be checked to insure that the unit is
operating properly.
Manifold Assembly Removal
To remove the manifold
1. Shut off gas and electric supply.
2. Disconnect gas manifold at ground union joint.
3. Remove the two screws holding the manifold to the heat
exchanger support.
4. Slide the manifold through the manifold bracket.
5. Clean the orifices and adjust the air shutters as necessary.
6. Follow steps 3-6 in reverse order to install the manifold
assembly.
7. Turn on the electric and gas supply.
8. Check the ground joint union for leaks with a soap solution.
Tighten if necessary.
MAINTENANCE
All installation and service of these units must be performed by
a qualified installation and service agency. All heating equipment
should be serviced before each heating season to assure
proper operations. The following items may be required to have
more frequent service schedule based on the environment in
which the unit is installed, and the frequency of the equipment
operation.
Before any service, BE SURE TO TURN OFF GAS AT THE
MANUAL SHUT-OFF VALVE AHEAD OF THE COMBINATION
GAS CONTROL AND TURN OFF ALL ELECTRIC POWER TO
THE HEATER AND AIR MOVING SYSTEM.
Blower Assembly
The blower assembly includes the bearings, drive sheaves and
belts.
Blower bearings should be checked and lubricated based on the
blower manufacturer’s recommendations. Bearings should also
be checked for any unusual wear and replaced if needed.
Drive sheaves should be checked at the same time the bearings
are inspected. Check to make sure the sheaves are in alignment
and are securely fastened to the blower and motor shafts.
Belt tension should be rechecked shortly after the unit has been
installed to check for belt stretching. After the initial start-up,
monthly checks are recommended.
Filters
If the unit is supplied with a dirty filter switch and light, clean or
replace the filters any time the dirty filter light comes on.
Units which do not have a dirty filter warning light should have
the filters checked monthly. Clean or replace if necessary. In
dirty atmospheres, filter maintenance may be required more often.
IMPORTANT
To check most of the Possible Remedies in the troubleshooting
guide listed in Table 20.1, refer to the applicable sections of the
manual.
CAUTION
Do not attempt to reuse any mechanical or electrical controllers
which have been wet. Replace defective controller.
WARNING
When servicing or repairing this equipment, use only factory-
approved service replacement parts. A complete replacement
parts list may be obtained by contacting Modine Manufacturing
Company. Refer to the rating plate on the appliance for
complete appliance model number, serial number, and
company address. Any substitution of parts or controls not
approved by the factory will be at the owner’s risk.

19
5-564
BURNER SIDE
ACCESS PANEL
MANIFOLD
ELECTRICAL
JUNCTION
BOX
SERIAL PLATE
MAINTENANCE
Burner and Pilot Assembly Removal
To remove the burner
1. Shut off gas and electric supply.
2. Disconnect the pilot supply line from the gas valve.
3. Disconnect the ignition cable from the ignition controller
(located in the electrical junction box). Feed the cable through
the bushing in the bottom of the electrical junction box.
4. Remove the screws holding the burner side access panel.
Attached to the panel are the burner retaining pins that align
the burner.
5. Slide the burner assembly out. The pilot is attached to the
burner assembly.
6. Examine the burner and pilot assembly for cleanliness and/or
obstructions as necessary (see Duct Furnace for cleaning
instructions).
7. Replace the burner assembly in reverse order. In replacing
the burner, be certain that the rear burner slots are located
properly on the burner retaining pins. Do not force the burner
side access panel, it will not fit if the burner is not properly
aligned.
8. Reconnect the ignition cable and pilot gas supply line.
9. Turn on the electric and gas supply.
PILOT
SUPPLY
LINE
AIR SHUTTERS
(NOT SHOWN)
ARE LOCATED
ON THE
MANIFOLD
IGNITION
CABLE
PILOT
ASSEMBLY
Figure 19.1 - Manifold Assembly Removal

20 5-564
SERVICE & TROUBLESHOOTING
Trouble Possible Cause Possible Remedy
Table 20.1 - Troubleshooting
Power Exhauster Motor will not start 1. Power supply is off.
2. No 24V power to thermostat.
3. Thermostat malfunction.
4. Defective power exhauster relay.
5. Defective power exhauster motor.
1. Turn on main power.
2. Check control transformer.
3. Check/replace thermostat.
4. Replace power exhauster relay.
5. Replace power exhauster motor.
Pilot does not light/stay lit 1. Main gas is off.
2. Power supply is off.
3. Air in gas line.
4. Dirt in pilot orifice.
5. Gas pressure out of proper range.
6. Pilot valve does not open.
a. Defective ignition controller.
b. Defective gas valve.
7. No spark at ignitor.
a. Loose wire connections.
b. Pilot sensor is grounded.
c. Defective ignition controller.
8. Safety device has cut power.
9. Excessive drafts.
10. Pilot orifice fitting leak.
1. Open manual gas valve.
2. Turn on main power.
3. Purge gas line.
4. Check for plugged pilot orifice and clean
with compressed air if necessary.
5. Adjust to a maximum of 14" W.C.
Minimum for Natural Gas - 6" W.C.
Minimum for Propane Gas - 11" W.C.
6. Check wiring for 24 volts to valve.
a. Replace ignition controller.
b. Replace gas valve.
7. a. Check all ignition controller wiring.
b. Replace sensor if cracked or worn.
c. Replace ignition controller.
8. Check all safety devices (High limit, air flow
proving switch, differential pressure switch,
gas pressure switches, etc.) Determine and
correct problem. Reset if necessary.
9. Find source and re-direct airflow away from
unit.
10. Tighten pilot orifice. Flame impingment
on pilot sensor may cause pilot sensor to
become inoperative.
Main burners do not light (Pilot is lit) 1. Defective valve.
2. Loose wiring.
3. Defective pilot sensor.
4. Defective ignition controller.
5. Improper thermostat wiring.
1. Replace valve.
2. Check wiring to gas valve.
3. Replace pilot sensor.
4. Replace ignition controller.
5. Verify wiring compared to wiring diagram.
Lifting Flames (See Figure 21.1) 1. Too much primary air.
2. Main pressure set too high.
3. Orifice too large.
1. Reduce primary air.
2. Adjust to a maximum of 14" W.C.
3. Check orifice size with those listed on the
serial plate.
Yellow Tipping
(With propane gas, some yellow tipping
is always present.)
1. Insufficient primary air.
2. Dirty orifice.
3. Misaligned orifice.
1. Increase primary air.
2. Check orifices and clean with compressed
air if necessary.
3. Check manifold, replace if necessary.
Flashback 1. Too much primary air.
2. Main pressure set too high.
3. Orifice too large.
1. Reduce primary air.
2. Adjust to a maximim of 14” W.C.
3. Check orifice size with those listed on
the serial plate.
Floating Flames (See Figure 21.2) 1. Insufficient primary air.
2. Main pressure set too high.
3. Orifice too large.
4. Blocked vent.
1. Increase primary air.
2. Adjust to a maximum of 14" W.C.
3. Check orifice size with those listed on
the serial plate.
4. Clean/correct venting system.
Flame Rollout (See Figure 21.3) 1. Main pressure set too high.
2. Orifice too large.
3. Blocked vent.
1. Adjust to a maximum of 14" W.C.
2. Check orifice size with those listed on
the serial plate.
3. Clean/correct venting system.