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© 2025 Lennox Industries Inc.
Dallas, Texas USA
WARNING
installation,
Improper
service or maintenance can cause property damage,
personal injury or loss of life. Installation and service
must be performed by a licensed professional HVAC
installer (or equivalent), service agency or the gas
supplier.
Contents
Unit Dimensions - inches (mm........................................2
ML180UHVK Gas Furnace .............................................3
Shipping and Packing List ..............................................3
Safety .............................................................................3
Use of Furnace as a Construction Heaterl .....................4
General ...........................................................................4
Combustion, Dilution, Ventilation Air...............................5
Setting Equipment ..........................................................8
Filters ............................................................................ 11
Duct System .................................................................12
Venting .........................................................................13
Gas Piping ....................................................................20
adjustment,
alteration,
INSTALLATION
INSTRUCTIONS
ML180UHVK
MERIT
SERIES
®
HORIZONTAL AIR DISCHARGE
508547-01
05/2025
THIS MANUAL MUST BE LEFT WITH THE
HOMEOWNER FOR FUTURE REFERENCE
This is a safety alert symbol and should never be
ignored. When you see this symbol on labels or in man-
uals, be alert to the potential for personal injury or death.
This furnace is equipped with an ignition control
factory enabled for use with Lennox A2L refrigerant
systems.
Disabling
functionality on A2L system is prohibited by safety
codes. Refer to furnace installation instructions for
non-A2L and non-Lennox refrigerant system setup.
IMPORTANT
DO NOT use the heat exchanger bracket to lift, drag
or pull the furnace to its installation location. Doing
so will loosen the bracket causing noise and or
unsafe operation.
Bracket
Electrical .......................................................................22
Igition Control ...............................................................25
Low GWP Application ...................................................34
Unit Start-Up .................................................................37
Sequence of Operation.................................................38
Gas Pressure Measurement.........................................38
Proper Combustion.......................................................38
High Altitude .................................................................38
Other Unit Adjustments.................................................40
Service..........................................................................40
Blower Data ..................................................................43
Start Up and Performance Check list ...........................47
Page 1
GAS
FURNACE
WARNING
the
refrigerant
detection
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Table of Contents
Related Manuals for Lennox MERIT ML180UHVK
Summary of Contents for Lennox MERIT ML180UHVK
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Page 1: Table Of Contents
When you see this symbol on labels or in man- uals, be alert to the potential for personal injury or death. WARNING This furnace is equipped with an ignition control factory enabled for use with Lennox A2L refrigerant systems. Disabling refrigerant... -
Page 2: Unit Dimensions - Inches
Unit Dimensions - inches (mm) 3-1/8 (79) NOTE - 60C size units that require air volumes over 1800 cfm must have one of the following: 1. Single side return air and Optional Return Air Base with transition that must accommodate required 20 x 25 x 1 inch (508 x 635 x 25 mm) air filter to maintain proper velocity. -
Page 3: Ml180Uhvk Gas Furnace
Certifications ML180UHVK Gas Furnace ML180UHVK units are CSA International certified to ANSI The ML180UHVK unit is shipped ready for installation Z21.47. in the upflow or horizontal right position (for horizontal In the USA, installation of gas furnaces must conform with left position the combustion air pressure switch must be local building codes. -
Page 4: Use Of Furnace As A Construction Heaterl
Use of Furnace as Construction Heater distribution system as possible. The furnace should Lennox does not recommend the use of ML180UHVK also be located close to the chimney or vent termi- units as a construction heater during any phase of con- nation point. -
Page 5: Combustion, Dilution, Ventilation Air
• Do not install the furnace where drafts might blow CAUTION directly into it. This could cause improper combus- Insufficient combustion air can cause headaches, tion and unsafe operation. nausea, dizziness or asphyxiation. It will also cause • Do not block the furnace combustion air openings excess water in the heat exchanger resulting in with clothing, boxes, doors, etc. -
Page 6: Confined Space
Confined Space Air from Inside f the confined space that houses the furnace adjoins a A confined space is an area with a volume less than 50 space categorized as unconfined, air can be brought in cubic feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of by providing two permanent openings between the two the combined input rating of all appliances installed in that space. - Page 7 EQUIPMENT IN CONFINED SPACE ALL AIR FROM OUTSIDE (Inlet Air from Crawlspace and Outlet Air to Ventilated Attic) CHIMNEY OR GAS VENT VENTILATION LOUVERS (Each end of attic) OUTLET WATER FURNACE HEATER INLET VENTILATION LOUVERS (For unheated crawl space) AIR FLOW NOTE-The inlet and outlet air openings shall each have a free area of at least one square inch (645 ) per 4,000 Btu (1.17 kW) per hour of the total input rating of all equipment in the enclosure.
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Page 8: Setting Equipment
Upflow Applications Setting Equipment Allow for clearances to combustible materials as indicated WARNING on the unit nameplate. Minimum clearances for closet or alcove installations are shown in FIGURE 7. Do not install the furnace on its front or its back. Do not connect the return air ducts to the back of the Upflow Application Installation Clearances furnace. - Page 9 Return Air -- Upflow Applications Single Side Return Air Return air can be brought in through the bottom or either (with transition and filter) side of the furnace installed in an upflow application. If the furnace is installed on a platform with bottom return, make an airtight seal between the bottom of the furnace and the platform to ensure that the furnace operates properly and safely.
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Page 10: Horizontal Applications
Pivot the bottom cap down to release the bottom applications. Order horizontal suspension kit (51W10) panel. Once the bottom panel has been removed, reinstall from Lennox, or use equivalent suspension method. the bottom cap. See FIGURE 10. Allow for clearances to combustible materials as indicated on the unit nameplate. -
Page 11: Filters
In platform installations with bottom return air, the specifications provided by the filter manufacturer furnace should be sealed airtight to the return air against the data given in the appropriate Lennox plenum. A door must never be used as a portion of Product Specifications bulletin. -
Page 12: Duct System
Return Air Plenum Duct System NOTE - Return air must not be drawn from a roomwhere Use industry-approved standards (such as those pub- this furnace, or any other gas-fueled appliance (i.e., water lished by Air Conditioning Contractors of America or Amer- heater), or carbon monoxide producing device (i.e., wood ican Society of Heating, Refrigerating and Air Condition- fireplace) is installed. -
Page 13: Venting
1 - Remove the four mounting screws (FIGURE Venting 15) which secure the combustion air inducer / A 4-inch diameter flue transition is factory-installed on the pressure switch assembly to the orifice plate. Lift combustion air inducer outlet of all models. FIGURE 16 the assembly and rotate it 90 degrees clockwise shows the combustion air inducer as shipped from the or counterclockwise to either the 3 o’clock position... - Page 14 HORIZONTAL LEFT POSITION HORIZONTAL RIGHT POSITION Top Vent Discharge Top Vent Discharge Vent Pipe Vent Pipe Pressure Switch Pressure Flue Switch Transition Cover Plate Flue Transition Collector Box FLOW FLOW Make-Up Box Cover Plate Collector Box Make-Up Box Disconnect pressure switch hose from barbed fitting on the pressure switch assembly.
- Page 15 The ML180UHVK series units are classified as fan-assist- Venting Using a Masonry Chimney ed Category I furnaces when vertically vented according The following additional requirements apply when a lined to the latest edition of National Fuel Gas Code (NFPA 54 masonry chimney is used to vent this furnace.
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Page 16: General Venting Requirements
When inspection reveals that an existing chimney is not Common Venting Using Metal-Lined Masonry Chimney safe for the intended purpose, it shall be rebuilt to conform to nationally recognized standards, lined or relined with SEALED suitable materials, or replaced with a gas vent or chimney suitable for venting ML180UHVK series units. - Page 17 Common Venting Using Tile-Lined Interior Masonry Chimney and Combined Vent Connector MINIMUM LENGTH = AS SHORT AS PRACTICAL. INTERIOR TILE-LINED FOR MAXIMUM LENGTH SEE NOTE TO LEFT MASONRY CHIMNEY NOTE- Refer to provided venting tables for installations. NOTE - the chimney must be properly sized per provided venting tables or lined with listed metal lining system.
- Page 18 17 - If vent connectors are combined prior to entering 20 - Do not install a manual damper, barometric draft the common vent, the maximum common vent regulator or flue restrictor between the furnace and capacity listed in the common venting tables must the chimney.
- Page 19 TABLE 4 Vent Connector Capacity Type B Double-Wall Vents with Type B Double-Wall Connectors Serving Two or More Category I Appliances Vent and Connector Diameter - D (inches) Height Lateral 3 inch 4 inch 5 inch 6 inch Appliance Input Rating in Thousands of Btu Per Hour (feet) (feet) TABLE 5...
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Page 20: Gas Piping
Removal of the Furnace from Common Vent Gas Piping In the event that an existing furnace is removed from a Gas supply piping should not allow more than 0.5”W.C. venting system commonly run with separate gas applianc- drop in pressure between gas meter and unit. Supply gas es, the venting system is likely to be too large to properly pipe must not be smaller than unit gas connection. - Page 21 TABLE 6 Gas Pipe Capacity - ft3/hr (m3/hr) Nominal Internal Length of Pipe - feet (m) Iron Pipe Diameter Size Inches inches (3.048) (6.096) (9,144) (12,192) (15.240) (18.288) (21.336) (24.384) (27.432) (30,480) (mm) (mm) .622 (12.7) (17.799) (4.87) (3.34) (2.69) (2.29) (2.03) (1.84)
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Page 22: Electrical
Horizontal Applications Possible Gas Piping Configurations MANUAL MAIN SHUT-OFF VALVE MANUAL Horizontal Application MAIN SHUT-OFF Left-Side Air Discharge VALVE GROUND JOINT UNION GROUND JOINT DRIP LEG UNION DRIP LEG MANUAL MAIN SHUT-OFF VALVE FIELD PROVIDED GROUND JOINT INSTALLED UNION Horizontal Application NOTE - BLACK IRON PIPE ONLY TO BE ROUTED INSIDE OF CABINET DRIP LEG Right-Side Air Discharge... - Page 23 Proper polarity of the supply connections (“HOT” and INTERIOR MAKE-UP BOX INSTALLATION “NEUTRAL”) must be observed to ensure that safety controls provide the protection intended. Right Side A connection to the unit’s ground wire and actual earth ground (typically a ground stake or buried steel pipe) must be maintained for proper operation.
- Page 24 FIGURE 30 Page 24...
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Page 25: Ignition Control
IGNITION CONTROL Single Stage, Variable Speed, Non-Communicating 107791-01 FIGURE 31 TABLE 8 TABLE 7 THERMOSTAT INPUT TERMINALS 1/4” QUICK CONNECT TERMINALS HEAT COMMON GROUND 120V HUM POWER FOR HUMIDIFIER (120 VAC 24V AC LINE INCOMING POWER LINE (120 VAC) XFMR TRANSFORMER PRIMARY (120 VAC) LOW STAGE COOL (when W915 is clipped) CIRC... -
Page 26: Ignition Control Diagnostic Codes
IGNITION CONTROL DIAGNOSTIC CODES DIAGNOSTIC CODES / STATUS OF FURNACE CODE IDLE MODE (DECIMALBLINKS AT 1 HERTZ -- 0.5 SECONDS ON, 0.5 SECONDS OFF INDOOR BLOWER OPERATION: CONTINUOUS FAN MODE (COSTANT TORQUE ONLY) INDOOR BLOWER OPERATION: FOLLOWED BY CFM SETTING FOR INDOOR BLOWER (1 SECOND ON, 0.5 SECOND OFF) / CFM SETTING FOR MODE DISPLAYED (VARIALBE SPEED ONLY) COOLING/DEHUMIDIFICATION STAGE (1 SECOND ON, 0.5 SECOND OFF) 1 OR 2... -
Page 27: Fan Control
IGNITION CONTROL DIAGNOSTIC CODES (CONTINUED) SOFT LOCKOUT FAULTS (60 MINUTES) SOFT LOCKOUT-FLAME FAILURE ON IGNITION, IGNITION RETRY>MAX, LAST FAILED RETRY DUE TO FLAME E270 FAILURE SOFT LOCKOUT-PRESSURE SWITCH OPEN, IGNITION RETRY>MAX, LAST FAILED RETRY DUE TO LPSW OPEN E271 SOFT LOCKOUT-PRESSURE SWITCH OPEN, IN RUN MODE HEATING RECYCLES>MAX, LAST FAILED RETRY DUE E272 TO LPSW OPEN SOFT LOCKOUT-FLAME FAILURE IN RUN MODE,HEATING RECYCLES>MAX, LAST FAILED RETRY DUE TO LOSS... - Page 28 TABLE 11 Allowable Heating Speeds ML180V Model Speed Adjust MED LOW MED HIGH HIGH +10% Allowed 030V36A Norm Factory Setting Allowed -10% Allowed +10% Allowed 045V36A Norm Factory Setting -10% Allowed Not Allowed +10% Allowed 070V36A Norm Factory Setting -10% Allowed +10% Allowed...
- Page 29 DIP Switch Settings and On-Board Links On Board Links Must Be Cut To Select Thermostat Wiring Connections System Options 1 Heat / 1 Cool FURNACE OUTDOOR T'STAT TERM. STRIP UNIT DO NOT CUT ANY ON-BOARD LINKS 1 Heat / 2 Cool FURNACE OUTDOOR T'STAT...
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Page 30: System Options
DIP Switch Settings and On-Board Links Wiring Connections On Board Links Must Be Cut To Select Thermostat System Options Dual Fuel FURNACE HEAT PUMP T'STAT TERM. STRIP Single Stage Heat Pump CUT ON-BOARD LINK (M30 T-stat) W951 67M41* HEAT thermostat w/ PUMP bilities Capable of 2... - Page 31 DIP Switch Settings and On-Board Links Wiring Connections On Board Links Must Be Cut To Select Thermostat System Options Dual Fuel FURNACE HEAT PUMP T'STAT TERM. STRIP Single Stage Heat Pump CUT ON-BOARD LINK (M30 T-stat) W951 67M41* HEAT thermostat w/ PUMP bilities Capable of 2...
- Page 32 • Active Dehumidification - To achieve addition- Variable Speed Ignition Control Features al dehumidification, clip the DEHUM (W914) trace Accessory Terminals on the integrated ignition/ blower control board and connect a humidity control that opens on humidi- One line voltage “ACC” 1/4” spade terminal is provided ty rise to the DEHUM and DH/DS) terminals.
- Page 33 Adjust Tap - Airflow amounts may be increased or de- Single Stage Cooling creased by 10% by moving the ADJUST DIP switches 7 and 8. Changes to the ADJUST tap will affect both cooling and heating airflows. The TEST position (DIP7 7.5 minutes 100% and DIP8 both ON) shall not be used for normal fur-...
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Page 34: Low Gwp Application
Low GWP Application WARNING For use with Lennox approved evaporator coil and LGWP sensors only. Use original manufacturer recommended LGWP sensors if using non Lennox approved evaporator coil. CONNECTING THE FURNACE CONTROL BOARD SENSOR. See FIGURE 37 and follow steps below: FIGURE 36 1 - Route sensor wire #1 through provided grommet. - Page 35 FURNACE CONTROL BOARD LOW GWP MODES OF 2. After the furnace control board determines the OPERATION refrigerant levels are below the safety threshold, the blower will continue to operate for the remainder of the The modes of operation for the furnace control board are seven (7) -minute cycle.
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Page 36: Start-Up Procedure
LGWP TEST BUTTON FUNCTIONALITY External Alarm (For applications with external alarms wired directly to the The furnace control board is equipped with a Test/Reset furnace control board) push button. The Test button can be used to perform sev- The furnace control board triggers the external alarm sys- eral functions, depending on the mode of operation of the tem when it enters Leak Detected mode. -
Page 37: Unit Start-Up
5 - Remove the upper access panel. Unit Start-Up 6 - Move switch on gas valve to OFF. Do not force. See FOR YOUR SAFETY READ BEFORE LIGHTING FIGURE 38 and FIGURE 39. WARNING 7 - Wait five minutes to clear out any gas. If you then smell gas, STOP! Immediately call your gas supplier Do not use this furnace if any part has been from a neighbor’s phone. -
Page 38: Sequence Of Operation
1 - When thermostat calls for heat, combustion air NOTE - Pressure test adapter kit (10L34) is available from blower starts. Lennox to facilitate manifold pressure measurement. 2 - Combustion air pressure switch proves blower 1 - Connect test gauge to manifold pressure post on operation. - Page 39 IMPORTANT For safety, shut unit off and remove manometer as soon as an accurate reading has been obtained. Take care to replace pressure tap plug. TABLE 21 Supply Line and Manifold Pressure Settings at all Altitudes Line Pressure in. wg. Model 7501 - 10,000 0 - 2000 ft.
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Page 40: Other Unit Adjustments
the integrated control to begin the ignition sequence. Other Unit Adjustments Cooling Primary and Secondary Limits The unit is set up at the factory for single stage cooling. For The primary limit is located on the heating compartment two stage cooling operation, clip the Y1 to Y2 link locat- vestibule panel. - Page 41 Check for At the beginning of each heating season, and to comply air leaks on supply and return ducts and seal where with the Lennox Limited Warranty, your system should be necessary. checked by a licensed professional technician (or equiva-...
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Page 42: Burner Assembly & Removal
Cleaning the Burners 4 - To clean burners, run a vacuum cleaner with a soft brush attachment over the face of burners. Visually NOTE - Use papers or protective covering in front of the inspect inside the burners and crossovers for any furnace during cleaning. -
Page 43: Blower Data
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position. Continuous Fan Only speed is approximately 38% of the same second stage COOL speed position - minimum 350 cfm. Lennox Harmony III™ Zoning System Applications - Minimum blower speed is 350 cfm. BL O WER D ATA... - Page 44 First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position. Continuous Fan Only speed is approximately 38% of the same second stage COOL speed position - minimum 350 cfm. Lennox Harmony III™ Zoning System Applications - Minimum blower speed is 350 cfm. BL O WER D ATA...
- Page 45 First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position. Continuous Fan Only speed is approximately 38% of the same second stage COOL speed position - minimum 400 cfm. Lennox Harmony III™ Zoning System Applications - Minimum blower speed is 400 cfm. BL O WER D ATA...
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Page 46: Cabinet Parts
Lennox Harmony III™ Zoning System Applications - Minimum blower speed is 550 cfm. Repair Parts List The following repair parts are available through Lennox dealers. When ordering parts, include the complete furnace model number listed on the CSA nameplate -- Example: . -
Page 47: Start Up And Performance Check List
Start-Up & Performance Check List UNIT SET UP (typical) Unit Model Number_______________ Serial Number___________________ SUPPLY Line Voltage upflow furnace shown Gas Supply Pressure Filter RETURN RETURN DUCT SYSTEM GAS SUPPLY SUPPLY AIR DUCT LP/Propane Gas Natural Gas Sealed Piping Connections Tight Insulated (if necessary) Leak Tested Registers Open and Unobstructed... - Page 48 Start-Up & Performance Check List UNIT OPERATION (typical) Combustion CO SUPPLY Thermostat Gas Manifold Pressure Temperatures upflow furnace shown Filter Blower Motor Amps Duct Static RETURN RETURN COOLING MODE HEATING MODE INDOOR BLOWER AMPS______ GAS MANIFOLD PRESSURE “W.C._____ TEMPERATURE DROP COMBUSTION SAMPLE CO CO PPM_______ ______...
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