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© 2024 Lennox Industries Inc.
Dallas, Texas USA
CAUTION
As with any mechanical equipment, contact with sharp
sheet metal edges can result in personal injury. Take
care while handling this equipment and wear gloves and
protective clothing.
Contents
Unit Dimensions - inches (mm) ......................................2
ML296UHVK Gas Furnace .............................................3
Shipping and Packing List ..............................................3
Safety .............................................................................3
Use of Furnace as a Construction Heater ......................4
General ...........................................................................5
Combustion, Dilution, Ventilation Air...............................5
Setting Equipment ..........................................................8
Filters ............................................................................13
Duct System .................................................................13
Pipe Fittings Specifications...........................................14
Joint Cementing Procedure ..........................................15
C C C C
I I I I
HI
HI
INSTALLATION
INSTRUCTIONS
ML296UHVK
MERIT
SERIES GAS FURNACE
®
UPFLOW / HORIZONTAL AIR DISCHARGE
508520-01
11/2024
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.
Improper installation, adjustment, alteration, 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.
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.
Venting Practices ..........................................................16
Gas Piping ....................................................................36
Electrical .......................................................................38
Ignition Control .............................................................41
Low GWP Application ...................................................51
Unit Start-Up .................................................................54
Gas Pressure Measurement.........................................55
Proper Combustion.......................................................56
High Altitude .................................................................56
Repair Parts List ...........................................................57
Sequence of Operation.................................................59
Service..........................................................................60
Blower Data ..................................................................63
Start Up & Performance Check List..............................65
Page 1
WARNING
WARNING
the
refrigerant
detection
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Summary of Contents for Lennox MERIT ML296UHVK
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Page 1: Table Of Contents
Installation and service must be performed by a licensed professional HVAC installer (or equivalent), service agency or the gas supplier. WARNING This furnace is equipped with an ignition control factory enabled for use with Lennox A2L refrigerant systems. Disabling refrigerant detection functionality on A2L system is prohibited by safety codes. -
Page 2: Unit Dimensions - Inches (Mm)
Unit Dimensions - inches (mm) 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 EXHAUST AIR 3-3/8 OUTLET with transition that must accommodate required (86) 20 x 25 x 1 inch (508 x 635 x 25 mm) air filter to maintain proper velocity. -
Page 3: Ml296Uhvk Gas Furnace
ML296UHVK Gas Furnace Shipping and Packing List Package 1 of 1 contains The ML296UHVK Category IV gas furnace is shipped ready for installation in the upflow or horizontal position. 1 - Assembled ML296UHVK unit The furnace is shipped with the bottom panel in place. The 1 - Bag assembly containing the following: bottom panel must be removed if the unit is to be installed 1 - Snap bushing... -
Page 4: Use Of Furnace As A Construction Heater
In order to ensure proper unit operation in non-direct vent applications, combustion and ventilation air supply must Heating Unit Installed Parallell to Air Handler Unit Dampers be provided according to the current National Fuel Gas (open during heating operation only) Code or CSA-B149 standard. -
Page 5: General
FAILURE TO FOLLOW THE ABOVE INSTALLATION IN- Chlorinated waxes and cleaners STRUCTIONS VOIDS THE MANUFACTURER’S EQUIP- Chlorine base swimming pool chemicals MENT LIMITED WARRANTY. LENNOX DISCLAIMS Water softening chemicals ALL LIABILITY IN CONNECTION WITH INSTALLER’S De-icing salts or chemicals FAILURE TO FOLLOW THE ABOVE INSTALLATION IN- STRUCTIONS. -
Page 6: Confined Space
A portion of this information has been reprinted with per- Confined Space mission from the National Fuel Gas Code (ANSI Z223.1/ A confined space is an area with a volume less than 50 NFPA 54). This reprinted material is not the complete and cubic feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of official position of the ANSI on the referenced subject, the combined input rating of all appliances installed in that... - Page 7 Air from Outside EQUIPMENT IN CONFINED SPACE (Inlet Air from Ventilated Crawlspace and Outlet Air to Outside) If air from outside is brought in for combustion and ventila- tion, the confined space shall be provided with two perma- nent openings. One opening shall be within 12” (305mm) Roof Terminated of the top of the enclosure and one within 12”...
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Page 8: Installation - Setting Equipment
The bolt and washer must be removed before the furnace EQUIPMENT IN CONFINED SPACE - ALL AIR FROM OUTSIDE is placed into operation. After the bolt and washer have (All Air Through Ventilated Attic) been removed, the rigid leg will not touch the blower hous- ing. -
Page 9: Setting Equipment
SETTING EQUIPMENT UPFLOW APPLICATION Place level on blower Place level on the front blower deck screws to check deck to check side to side forward tilt UNIT FRONT AIR FLOW 1/2” max. SIDE VIEW HORIZONTAL APPLICATION UNIT FRONT AIR FLOW 1/2”... - Page 10 Return Air Guidelines WARNING Return air can be brought in through the bottom or either Improper installation of the furnace can result in side of the furnace installed in an upflow application. If the furnace is installed on a platform with bottom return, make personal injury or death.
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Page 11: Removing The Bottom Panel
Optional Return Air Base CONDENSATE (Upflow Applications Only) TRAP FURNACE FRONT 23 (584) 3−1/4 IF BASE Overall (83) IS USED (Maximum) Minimum WITHOUT 11 (279) IAQ CABINET, Maximum INDOOR AIR 22−7/16 A SINGLE Unit side return air 14 (356) (570) QUALITY RETURN AIR Opening... - Page 12 FIGURE 18, or install the furnace on a platform, as shown in FIGURE 19. A horizontal sus- pension kit (51W10) may be ordered from Lennox or use equivalent. Page 12...
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Page 13: Filters
If a gas appliance is operating in the data given in the appropriate Lennox Product a room with negative pressure, the flue products can be Specifications bulletin. Additional information is provided pulled back down the vent pipe and into the room. -
Page 14: Pipe Fittings Specifications
Return air can be brought in through the bottom or either TABLE 2 side of the furnace (return air brought into either side of PIPING AND FITTINGS SPECIFICATIONS furnace allowed only in upflow applications). If a furnace Schedule 40 PVC (Pipe) D1785 with bottom return air is installed on a platform, make an airtight seal between the bottom of the furnace and the... -
Page 15: Joint Cementing Procedure
TABLE 3 OUTDOOR TERMINATION USAGE* STANDARD CONCENTRIC Wall Kit 1-1.2 inch 2 inch 3 inch Flush Mount Vent Pipe Dia. 2 inch 3 inch Input Size Field 71M80 (US) 69M29 (US) 60L46 (US) 51W11 (US) Fabricated 22G44 (US) 44J40 (US) 444W92 (CA) 444W92 (CA) 444W93 (CA) -
Page 16: Venting Practices
8 - After assembly, wipe excess cement from pipe at Conduct the following test while each appliance is oper- end of fitting socket. A properly made joint will show ating and the other appliances (which are not operating) a bead around its entire perimeter. Any gaps may remain connected to the common venting system. -
Page 17: Vent Piping Guidelines
Resize the common venting system to the minimum vent Vent Piping Guidelines pipe size determined by using the appropriate tables in NOTE - Lennox has approved the use of DuraVent ® Appendix G. (These are in the current standards of the Centrotherm manufactured vent pipe and terminations National Fuel Gas Code ANSI Z223.1. - Page 18 Intake or exhaust? FIGURE 23 NOTE - Lennox offers a glueless vent adapter kit 17H92 How many elbows? as an option for exhaust exiting at the furnace top cap Count all elbows inside coupling. If the kit is not used the exhaust pipe MUST be and outside house.
- Page 19 TABLE 5 Maximum Allowable Intake or Exhaust Vent Length in Feet NOTE - Size intake and exhaust pipe length separately. Values in table are for Intake OR Exhaust, not combined total. Both Intake and Exhaust must be same pipe size Standard Termination at Elevation 0 - 4500 ft No Of 1-1/2”...
- Page 20 TABLE 5 Continued Maximum Allowable Intake or Exhaust Vent Length in Feet NOTE - Size intake and exhaust pipe length separately. Values in table are for Intake OR Exhaust, not combined total. Both Intake and Exhaust must be same pipe size. Concentric Termination at Elevation 0 - 4500 ft No Of 1-1/2”...
- Page 21 TABLE 6 Maximum Allowable Exhaust Vent Lengths With Furnace Installed in a Closet or Basement Using Ventilated Attic or Crawl Space For Intake Air in Feet NOTE - Size intake and exhaust pipe length separately. Values in table are for Intake OR Exhaust, not combined total. Both Intake and Exhaust must be same pipe size.
- Page 22 TYPICAL EXHAUST AND INTAKE PIPE CONNECTIONS IN UPFLOW DIRECT OR NON-DIRECT VENT APPLICATIONS 2” 2” EXHAUST EXHAUST INTAKE INTAKE 2” 2” 2” 2” 3” 3” 045/070 Only 1−1/2” TRANSITION Exhaust 2” 6” Min Exhaust DO NOT transition from larger to smaller DO NOT transition pipe in horizontal runs from smaller to larger...
- Page 23 Intake Piping TYPICAL AIR INTAKE PIPE CONNECTIONS HORIZONTAL NON−DIRECT VENT APPLICATIONS The ML296UHVK furnace may be installed in either direct (Horizontal Right−Hand Air Discharge Application Shown) vent or non-direct vent applications. In non-direct vent ap- plications, when intake air will be drawn into the furnace from the surrounding space, the indoor air quality must be considered and guidelines listed in Combustion, Dilution PVC pipe...
- Page 24 General Guidelines for Vent Terminations CAUTION In Non-Direct Vent applications, combustion air is taken If this unit is being installed in an application with from indoors or ventilated attic or crawlspace and the flue combustion air coming in from a space serviced by an gases are discharged to the outdoors.
- Page 25 TABLE 7 Maximum Allowable Exhaust Vent Pipe Length (in ft. ) Without Insulation In Unconditioned Space For Winter Design Temperatures Two - Stage High Efficiency Furnace Winter Design Unit Input Size Vent Pipe Tempera- Diameter tures1 °F (°C) 1-1/2 32 to 21 2 in (0 to -6) 2-1/2 in...
- Page 26 ‡ Permitted only if veranda, porch, deck or balcony is fully open NOTE - This figure is intended to illustrate clearance on a minimum of two sides beneath the floor. Lennox recommends requirement and does not serve as a substitute for avoiding this location if possible.
- Page 27 ‡ Permitted only if veranda, porch, deck or balcony is fully open on a minimum of locally adopted installation codes. two sides beneath the floor. Lennox recommends avoiding this location if possible. FIGURE 33 Page 27...
- Page 28 Details of Intake and Exhaust Piping Terminations for At least one bracket must be used within 6” from the Direct Vent Installations top of the elbow and then every 24” (610mm) as shown in FIGURE 42, to prevent any movement in any direc- NOTE - In Direct Vent installations, combustion air is taken tion.
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Page 29: Exhaust Vent
TABLE 8 EXHAUST PIPE TERMINATION SIZE REDUCTION FIELD-PROVIDED Accelerator not required REDUCER MAY BE ML296UHVK Model Termination Pipe Size for 3” concentric REQUIRED TO ADAPT DIFFERENT VENT PIPE *045 and 070 1-1/2” (38MM) OUTSIDE SIZE TO TERMINATION INTAKE WALL *090 2”... - Page 30 FIELD FABRICATED WALL TERMINATION NOTE − FIELD−PROVIDED REDUCER MAY BE 2” (51mm) 3” (76mm) REQUIRED TO ADAPT LARGER VENT PIPE SIZE Vent Pipe Vent Pipe TO TERMINATION A− Minimum clearance above grade or average 12” (305 mm) 12” (305 mm) snow accumulation B−...
- Page 31 KIT 15Z70 Crawl Space and Extended Horizontal Venting (CANADA) Lennox provides kit 51W18 to install 2” or 3” PVC exhaust piping through the floor joists and into the crawl space. See FIGURE 45. This kit can also be used as a supplemental drain for in- FIGURE 45 stallations with condensate run back in the vent pipe (ie.
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Page 32: Condensate Piping
Condensate Piping CONDENSATE TRAP AND PLUG LOCATIONS This unit is designed for either right- or left-side exit of (Unit shown in upflow position) condensate piping in upflow applications. In horizontal Trap applications, the condensate trap must extend below the (same on unit. - Page 33 (Unit shown in upflow position with remote trap) ble, a heat cable kit may be used on the condensate trap and line. Heating cable kit is available from Lennox in var- ious lengths; 6 ft. (1.8m) - kit no. 26K68; 24 ft. (7.3m) - kit FieldProvidedVent no.
- Page 34 IMPORTANT Furnace with Evaporator Coil Using a Common Drain When combining the furnace and evaporator coil drains together, the A/C condensate drain outlet must Evaporator drain be vented to relieve pressure in order for the furnace line required pressure switch to operate properly. (Trap at coil is optional) Condensate Trap With Optional Overflow Switch (1”...
- Page 35 TRAP / DRAIN ASSEMBLY USING 1/2” PVC OR 3/4” PVC Optional Condensate Drain Connection Adapter 3/4 inch slip X 3/4 inch mpt (not furnished) 90° Street Elbow 3/4 inch PVC (not furnished) Adapter 3/4 inch slip X 3/4 inch mpt (not furnished) Condensate Drain Connection In Unit 1 (25 mm) Min.
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Page 36: Gas Piping
IMPORTANT Gas Piping Gas supply piping should not allow more than 0.5”W.C. Compounds used on threaded joints of gas piping must drop in pressure between gas meter and unit. Supply gas be resistant to the actions of liquefied petroleum gases. pipe must not be smaller than unit gas connection. - Page 37 Upflow Application Upflow Application Left Side Piping Right Side Piping (Standard) (Alternate) 1/2” NPT 1/2” NPT MANUAL MAIN SHUT-OFF VALVE MANUAL MAIN SHUT-OFF VALVE GROUND GROUND JOINT JOINT UNION UNION DRIP LEG FIELD PROVIDED AND INSTALLED DRIP LEG NOTE - BLACK IRON PIPE ONLY TO BE ROUTED INSIDE OF CABINET FIGURE 56 Horizontal Applications Possible Gas Piping Configurations...
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Page 38: Electrical
TABLE 9 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) - Page 39 NOTE - Unit nameplate states maximum current draw. Generator Use - Voltage Requirements Maximum over-current protection allowed is shown in TA- The following requirements must be kept in mind when BLE 10. specifying a generator for use with this equipment: •...
- Page 40 FIGURE 59 Page 40...
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Page 41: Ignition Control
Bank Of Eight DIP Switches SW2 IGNITION CONTROL Switches 1 and 2 - Cooling Mode Blower Speed - The Integrated Control Switch Settings unit is shipped from the factory with the dip switches po- Conventional Thermostat sitioned for high speed (4) indoor blower motor operation during the cooling mode. - Page 42 TABLE 15 Heat Speed DIP Switch 7 DIP Switch 8 Medium High High Medium Low TABLE 16 Allowable Heating Speeds ML296UHVK Speed Adjust Setting “D” Setting “C” Setting “B” Setting “A” Model +10% Allowed 045XV36B Norm Factory Setting Allowed -10% Allowed +10% 070XV36B...
- Page 43 Two Stage, Variable Speed, Non-Communicating 107629-01 FIGURE 60 TABLE 17 TABLE 18 1/4” QUICK CONNECT TERMINALS THERMOSTAT INPUT TERMINALS LOW STAGE HEAT LINE 120VAC INPUT TO THE CONTROL HIGH STAGE HEAT XFMR 120VAC OUTPUT TO THE TRANSFORMER CIRC 120VAC OUTPUT TO THE INDOOR BLOWER BLOWER LOW STAGE COOL (when W915 is clipped) UNPOWERED NORMALLY OPEN (DRY)
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Page 44: Ignition Control Diagnostic Codes
IGNITION CONTROL DIAGNOSTIC CODES Low GWP Test Page 44... - Page 45 Any accessory rated up to one amp can be connected to On-Board Links this terminal with the neutral leg of the circuit being con- nected to one of the provided neutral terminals. If an ac- WARNING cessory rated at greater than one amp is connected to this terminal, it is necessary to use an external relay.
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Page 46: Wiring Connections
Field Wiring Applications With Conventional Thermostat (see Ignition Control section for DIP switch settings) DIP Switch Settings and On-Board Links DIP Switch 1 On Board Links Must Be Cut To Select Thermostat Thermostat Wiring Connections System Options Heating Stages 1 Heat / 1 Cool FURNACE OUTDOOR T'STAT... - Page 47 Field Wiring Applications With Conventional Thermostat (see Ignition Control section for DIP switch settings) DIP Switch Settings and On-Board Links DIP Switch 1 On Board Links Must Be Cut To Select Thermostat Thermostat Wiring Connections System Options Heating Stages 2 Heat / 2 Cool FURNACE OUTDOOR T'STAT...
- Page 48 Field Wiring Applications With Conventional Thermostat (see Ignition Control section for DIP switch settings) DIP Switch Settings and On-Board Links DIP Switch 1 Thermostat On Board Links Must Be Cut To Select Wiring Connections Thermostat Heating System Options Stages FURNACE Dual Fuel HEAT PUMP T'STAT...
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Page 49: System Options
Field Wiring Applications With Conventional Thermostat (see Ignition Control section for DIP switch settings) DIP Switch Settings and On-Board Links DIP Switch 1 On Board Links Must Be Cut To Select Wiring Connections Thermostat Thermostat Heating System Options Stages FURNACE Dual Fuel HEAT PUMP T'STAT... -
Page 50: 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 63 and follow steps below: 1 - Route sensor wire #1 through provided grommet. - Page 51 FURNACE CONTROL BOARD LOW GWP MODES OF 2. The furnace control board activates the blower (high OPERATION speed). The blower purges refrigerant from the cabinet, plenum, and ductwork. The modes of operation for the furnace control board are Initializing, Normal, Leak Detected, and Fault. 3.
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Page 52: 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 53: Unit Start-Up
6 - Adjust the thermostat to deactivate the heating Unit Start-Up demand and wait for the combustion air inducer to FOR YOUR SAFETY READ BEFORE OPERATING stop. At this point, the trap should be primed with sufficient water to ensure proper condensate drain WARNING operation. -
Page 54: Supply Pressure Measurement
NOTE - Pressure test adapter kit (10L34) is available from 6 - Is gas turned on at the meter? Lennox to facilitate manifold pressure measurement. 7 - Is the manual main shut-off valve open? A manifold pressure post located on the gas valve pro- 8 - Is the internal manual shut-off valve open? vides access to the manifold pressure. -
Page 55: Proper Combustion
Proper Combustion High Altitude Information Furnace should operate minimum 15 minutes with correct NOTE - In Canada, certification for installations at eleva- manifold pressure and gas flow rate before checking com- tions over 4500 feet (1372 m) is the jurisdiction of local bustion. -
Page 56: Testing For Proper Venting And Sufficient Combustion Air For Non-Direct Vent Applications
1 - Seal any unused openings in the venting system. Testing Proper Venting Sufficient 2 - Visually inspect the venting system for proper size and Combustion Air for Non-Direct Vent Applications horizontal pitch. Determine there is no blockage or WARNING restriction, leakage, corrosion, or other deficiencies which could cause an unsafe condition.3 - To the extent that it is practical, close all building doors and... -
Page 57: Repair Parts List
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: ML296UH045XV36BK. All service must be performed by a licensed professional installer (or equivalent), service agency, or gas supplier. -
Page 58: Sequence Of Operation
The circulating blower operates at full 1st stage heat Other Unit Adjustments speed until either the heat call is satisfied or the thermo- Primary Limit. stat initiates a call for 2nd stage heat. On a call for 2nd stage heat, the control energizes the circulating air blower The primary limit is located on the heating compartment on full CFM 2nd stage heat. -
Page 59: Service
At the beginning of each heating season, and to comply R to Y circuit on the control board. The control waits for with the Lennox Limited Warranty, your system should a 2- second delay before energizing the circulating blow- be checked as follows: er. - Page 60 12- Check the condition of the furnace cabinet insulation Cleaning The Burner Assembly and repair if necessary. If cleaning the burner assembly becomes necessary, fol- 13- Perform a complete combustion analysis during the low the steps below: furnace inspection to ensure proper combustion 1 - Turn off electrical and gas power supplies to furnace.
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Page 61: Approved Carbon Monoxide Detectors
Requirements for Commonwealth of Massachusetts Modifications to NFPA-54, Chapter 10 4 - INSPECTION. The state or local gas inspector of the side wall, horizontally vented, gas-fueled equipment Revise NFPA-54 section 10.8.3 to add the following shall not approve the installation unless, upon requirements: inspection, the inspector observes carbon monoxide For all side wall, horizontally vented, gas-fueled equip-... - Page 62 See below for venting in all provinces of Canada. For exterior horizontal venting applications, the 2” X 1.5” Lennox approves the following termination for use in all reducer for 2” venting at the point where the exhaust pipe provinces of Canada.
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Page 63: 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. Lennox LZSV Variable Zoning System Applications - Minimum blower speed is 300 cfm. - Page 64 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. Lennox LZSV Variable Zoning System Applications - Minimum blower speed is 380 cfm.
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Page 65: Start Up & Performance Check List
Start-Up & Performance Check List UNIT SET UP (typical) Furnace: Model Number_______________ Serial Number_________________ SUPPLY Line Voltage GAS SUPPLY LP Propane Gas Natural Gas Piping Connections Tight Leak Tested Flter Supply Line Pressure “W.C.________ RETURN AIR Gas Supply Pressure DUCT SYSTEM SUPPLY AIR DUCT Sealed INTAKE / EXHAUST PIPE... -
Page 66: Unit Operation
UNIT OPERATION HEATING MODE COOLING MODE GAS MANIFOLD PRESSURE “W.C._____ INDOOR BLOWER AMPS______ COMBUSTION SAMPLE CO CO PPM_______ TEMPERATURE DROP ______ Return Duct Temperature _________ INDOOR BLOWER AMPS______ Supply Duct Temperature _______ Temperature Drop = _________ TEMPERATURE RISE TOTAL EXTERNAL STATIC (dry coil) Supply Duct Temperature ________ Supply External Static _______ Return Duct Temperature...
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