Lennox SL297UHNV Series Installation and operation manual

Page 1 ©2021 Lennox Industries Inc.
Corp. 1802-L1
Revised 02/2021
SL297UHNV
Service Literature
COMMUNICATING ENABLED SL297UHNV SERIES UNITS
SL297UHNV series units are 90% efficiency gas furnaces
used for upflow or horizontal applications only.
SL297UHNV units are available in heating capacities of
40,000 to 80,000 Btuh and cooling applications up to 4
tons. Refer to Product Specifications Manual for proper siz
ing.
Units are factory equipped for use with natural gas.
SL297UHNV model units are equipped with a communicat
ing enabled SureLight®two-stage variable speed integrated
control. All units use a redundant gas valve to assure safety
shut-off as required by C.S.A.
All specifications in this manual are subject to change. Pro
cedures outlined in this manual are presented as a recom
mendation only and do not supersede or replace local or
state codes. In the absence of local or state codes, the
guidelines and procedures outlined in this manual (except
where noted) are recommendations only and do not consti
tute code.
TABLE OF CONTENTS
Specifications Page 2.............................
I Unit Components Page 11.......................
II Installation Page 33.............................
III Start Up Page 51..............................
IV Heating System Service Checks Page 52.........
V Typical Operating Characteristics Page 58.........
VI Maintenance Page 58..........................
VII Wiring and Sequence of Operation Page 61......
VIII Field Wiring and Jumper Settings Page 66.......
IX Program Unit Capacity Size Mode Page 70.......
X Troubleshooting Page 71........................
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, person
al injury or loss of life. Installation and service must
be performed by a licensed professional HVAC in
staller (or equivalent), service agency or the gas sup
plier.
CAUTION
As with any mechanical equipment, contact with
sharp sheet metal edges can result in personal in
jury. Take care while handling this equipment and
wear gloves and protective clothing.

Page 2
SPECIFICATIONS
Gas
Heating
Performance
Model No. SL297UH040NV36B SL297UH060NV36B
1AFUE 97.5% 97.5%
High
Fire
Input - Btuh 40,000 60,000
Output - Btuh 39,000 58,000
Temperature rise range - °F 30-60 50-80/25-55
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
3.5 3.5
Low
Fire
Input - Btuh 26,000 39,000
Output - Btuh 25,000 38,000
Temperature rise range - °F 20 - 50 25 - 55
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
1.5 1.5
High static - in. w.g. Heating 0.8 0.8
Cooling 1.0 1.0
Connections
in.
Intake / Exhaust Pipe (PVC) 2 / 2 2 / 2
Gas pipe size IPS 1/2 1/2
Condensate Drain Trap (PVC pipe) - i.d. 3/4 3/4
with furnished 90° street elbow 3/4 slip x 3/4 Mipt 3/4 slip x 3/4 Mipt
with eld supplied (PVC coupling) - o.d. 3/4 slip x 3/4 MPT 3/4 slip x 3/4 MPT
Indoor
Blower
Wheel nominal diameter x width - in. 10 x 9 10 x 9
Motor output - hp 1/2 1/2
Tons of add-on cooling 2 - 3 2 - 3
Air Volume Range - cfm 440-1370 475-1380
Electrical Data Voltage 120 volts - 60 hertz - 1 phase
Blower motor full load amps 7.7 7.7
Maximum overcurrent protection 15 15
Shipping Data lbs. - 1 package 125 130
NOTE - Filters and provisions for mounting are not furnished and must be eld provided.
1 Annual Fuel Utilization Efciency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized
furnaces.
Gas
Heating
Performance
Model No. SL297UH080NV48C SL297UH080NV60C
1AFUE 97.5% 97.5%
High
Fire
Input - Btuh 80,000 80,000
Output - Btuh 78,000 78,000
Temperature rise range - °F 45-75 40-70
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
3.5 3.5
Low
Fire
Input - Btuh 52,000 52,000
Output - Btuh 51,000 51,000
Temperature rise range - °F 30 - 60 25 - 55
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
1.5 1.5
High static - in. w.g. Heating 0.8 0.8
Cooling 1.0 1.0
Connections
in.
Intake / Exhaust Pipe (PVC) 2 / 2 2 / 2
Gas pipe size IPS 1/2 1/2
Condensate Drain Trap (PVC pipe) - i.d. 3/4 3/4
with furnished 90° street elbow 3/4 slip x 3/4 Mipt 3/4 slip x 3/4 Mipt
with eld supplied (PVC coupling) - o.d. 3/4 slip x 3/4 MPT 3/4 slip x 3/4 MPT
Indoor
Blower
Wheel nominal diameter x width - in. 11 x 11 11 x 11
Motor output - hp 3/4 1
Tons of add-on cooling 2.5 - 4 3 - 5
Air Volume Range - cfm 620-1730 870-2285
Electrical Data Voltage 120 volts - 60 hertz - 1 phase
Blower motor full load amps 10.1 12.8
Maximum overcurrent protection 15 15
Shipping Data lbs. - 1 package 154 156
NOTE - Filters and provisions for mounting are not furnished and must be eld provided.
1 Annual Fuel Utilization Efciency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized
furnaces.

Page 3
OPTIONAL ACCESSORIES - ORDER SEPARATELY
NOTE - FURNACES CANNOT BE TWINNED!
“B” Width
Models
“C” Width
Models
CABINET ACCESSORIES
Horizontal Suspension Kit - Horizontal only 51W10 51W10
Return Air Base - Upow only 50W98 50W99
High Performance Economizer (Commercial Only) 10U53 10U53
CONDENSATE DRAIN KITS
Condensate Drain Heat Cable 6 ft. 26K68 26K68
24 ft. 26K69 26K69
Crawl Space Vent Drain Kit US 51W18 51W18
Canada 15Z70 15Z70
CONTROLS
iComfort®Communicating Thermostat 12U67 12U67
iComfort Wi-Fi®Thermostat 10F81 10F81
1Remote Outdoor Air Temperature Sensor
(for dual fuel and Humiditrol®)
X2658 X2658
2Discharge Air Temperature Sensor 88K38 88K38
ComfortSense®7500 Thermostat 13H14 13H14
3Remote Outdoor Temperature Sensor
(for dual fuel and Humiditrol)
X2658 X2658
FILTER KITS
4Air Filter and
Rack Kit
Horizontal (end) Size of lter - in. 87L96 - 18 x 25 x 1 87L97 - 20 x 25 x 1
Side Return Single 44J22 44J22
Ten Pack 66K63 66K63
Size of lter - in. 16 x 25 x 1 16 x 25 x 1

Page 4
BLOWER DATA
SL297UH040NV36B BLOWER PERFORMANCE (less lter)
BOTTOM RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1Heating Speed
DIP Switch
Settings
First Stage Heating Speed - cfm Second Stage Heating Speed - cfm
+24% 1151 1153
+18% 1101 1099
+12% 816 1041
+6% 771 999
Factory Default 704 944
–6% 651 887
–12% 578 826
–18% 542 757
COOLING
1Cooling Speed
DIP Switch
Settings
First Stage Cooling Speed - cfm Second Stage Cooling Speed - cfm
Low Medium-Low Medium-High 2High Low Medium-Low Medium-High 2High
+ 549 732 862 970 907 1072 1233 1373
Factory Default 521 637 760 873 830 975 1117 1268
– 441 560 684 784 736 874 1014 1142
SL297UH040NV36B BLOWER PERFORMANCE (less lter)
SINGLE SIDE RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1Heating Speed
DIP Switch
Settings
First Stage Heating Speed - cfm Second Stage Heating Speed - cfm
+24% 863 1129
+18% 807 1087
+12% 761 1021
+6% 713 775
Factory Default 716 723
–6% 683 686
–12% 589 599
–18% 562 558
COOLING
1Cooling Speed
DIP Switch
Settings
First Stage Cooling Speed - cfm Second Stage Cooling Speed - cfm
Low Medium-Low Medium-High 2High Low Medium-Low Medium-High 2High
+ 554 705 841 958 868 1057 1217 1344
Factory Default 509 606 724 875 799 969 1109 1253
– 436 559 675 754 703 860 1002 1137
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specic DIP Switch Settings.
2 Factory default setting.
NOTES - The effect of static pressure is included in air volumes shown.
First stage HEAT is approximately 91% of the same second stage HEAT.
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 selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 250 cfm.
Lennox iHarmony® Zoning System Applications - Minimum blower speed is 250 cfm.

Page 5
BLOWER DATA
SL297UH040NV36B BLOWER PERFORMANCE (less lter)
SINGLE SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1Heating Speed
DIP Switch
Settings
First Stage Heating Speed - cfm Second Stage Heating Speed - cfm
+24% 886 905
+18% 825 859
+12% 802 819
+6% 769 770
Factory Default 688 736
–6% 634 678
–12% 635 605
–18% 547 553
COOLING
1Cooling Speed
DIP Switch
Settings
First Stage Cooling Speed - cfm Second Stage Cooling Speed - cfm
Low Medium-Low Medium-High 2High Low Medium-Low Medium-High 2High
+ 542 698 835 947 886 1034 1201 1320
Factory Default 462 634 735 855 808 949 1096 1248
– 413 534 678 779 734 868 987 1130
SL297UH060NV36B BLOWER PERFORMANCE (less lter)
BOTTOM RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1Heating Speed
DIP Switch
Settings
First Stage Heating Speed - cfm Second Stage Heating Speed - cfm
+24% 1106 1234
+18% 1047 1158
+12% 989 1110
+6% 940 1054
Factory Default 886 999
–6% 837 947
–12% 780 882
–18% 722 826
COOLING
1Cooling Speed
DIP Switch
Settings
First Stage Cooling Speed - cfm Second Stage Cooling Speed - cfm
Low Medium-Low Medium-High 2High Low Medium-Low Medium-High 2High
[phone] 1046 1212 1380
Factory Default 554 681 783 883 816 952 1107 1254
– 486 630 712 802 739 876 1006 1132
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specic DIP Switch Settings.
2 Factory default setting.
NOTES - The effect of static pressure is included in air volumes shown.
First stage HEAT is approximately 91% of the same second stage HEAT.
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 selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 250 cfm.
Lennox iHarmony® Zoning System Applications - Minimum blower speed is 250 cfm.

Page 6
BLOWER DATA
SL297UH060NV36B BLOWER PERFORMANCE (less lter)
SINGLE SIDE RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1Heating Speed
DIP Switch
Settings
First Stage Heating Speed - cfm Second Stage Heating Speed - cfm
+24% 1114 1237
+18% 1063 1168
+12% 1010 1106
+6% 951 1064
Factory Default 892 1003
–6% 837 942
–12% 761 869
–18% 693 809
COOLING
1Cooling Speed
DIP Switch
Settings
First Stage Cooling Speed - cfm Second Stage Cooling Speed - cfm
Low Medium-Low Medium-High 2High Low Medium-Low Medium-High 2High
+ 599 749 867 981 892 1057 1229 1404
Factory Default 549 656 754 866 775 958 1115 1279
– 475 609 680 773 708 854 1011 1147
SL297UH060NV36B BLOWER PERFORMANCE (less lter)
SINGLE SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1Heating Speed
DIP Switch
Settings
First Stage Heating Speed - cfm Second Stage Heating Speed - cfm
+24% 1098 1229
+18% 1039 1168
+12% 992 1104
+6% 930 1051
Factory Default 885 996
–6% 822 937
–12% 773 878
–18% 717 817
COOLING
1Cooling Speed
DIP Switch
Settings
First Stage Cooling Speed - cfm Second Stage Cooling Speed - cfm
Low Medium-Low Medium-High 2High Low Medium-Low Medium-High 2High
+ 578 746 847 957 889 1042 1197 1364
Factory Default 556 665 764 864 799 949 1093 1249
– 485 593 706 783 721 845 988 1122
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specic DIP Switch Settings.
2 Factory default setting.
NOTES - The effect of static pressure is included in air volumes shown.
First stage HEAT is approximately 91% of the same second stage HEAT.
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 selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 250 cfm.
Lennox iHarmony® Zoning System Applications - Minimum blower speed is 250 cfm.

Page 7
BLOWER DATA
SL297UH080NV48C BLOWER PERFORMANCE (less lter)
BOTTOM RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1Heating Speed
DIP Switch
Settings
First Stage Heating Speed - cfm Second Stage Heating Speed - cfm
+24% 1499 1640
+18% 1427 1546
+12% 1361 1472
+6% 1294 1399
Factory Default 1219 1315
–6% 1176 1242
–12% 1090 1173
–18% 1007 1077
COOLING
1Cooling Speed
DIP Switch
Settings
First Stage Cooling Speed - cfm Second Stage Cooling Speed - cfm
Low Medium-Low Medium-High 2High Low Medium-Low Medium-High 2High
+ 797 954 1071 1241 1102 1304 1508 1713
Factory Default 713 873 969 1147 1006 1186 1392 1588
– 623 767 880 1025 911 1068 1252 1422
SL297UH080NV48C BLOWER PERFORMANCE (less lter)
SINGLE SIDE RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1Heating Speed
DIP Switch
Settings
First Stage Heating Speed - cfm Second Stage Heating Speed - cfm
+24% 1433 1542
+18% 1353 1480
+12% 1275 1398
+6% 1229 1334
Factory Default 1154 1253
–6% 1093 1181
–12% 1024 1107
–18% 958 1054
COOLING
1Cooling Speed
DIP Switch
Settings
First Stage Cooling Speed - cfm Second Stage Cooling Speed - cfm
Low Medium-Low Medium-High 2High Low Medium-Low Medium-High 2High
+ 792 959 1118 1264 1104 1302 1530 1730
Factory Default 844 876 1008 1162 1001 1202 1397 1612
– 643 771 908 1055 915 1090 1253 1443
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specic DIP Switch Settings.
2 Factory default setting.
NOTES - The effect of static pressure is included in air volumes shown.
First stage HEAT is approximately 91% of the same second stage HEAT.
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 selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 380 cfm.
Lennox iHarmony® Zoning System Applications - Minimum blower speed is 380 cfm.

Page 8
BLOWER DATA
SL297UH080NV48C BLOWER PERFORMANCE (less lter)
SINGLE SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1Heating Speed
DIP Switch
Settings
First Stage Heating Speed - cfm Second Stage Heating Speed - cfm
+24% 1,407 1,528
+18% 1,342 1,461
+12% 1,283 1,388
+6% 1,217 1,304
Factory Default 1,152 1,237
–6% 1,080 1,150
–12% 1,015 1,114
–18% 953 1,038
COOLING
1Cooling Speed
DIP Switch
Settings
First Stage Cooling Speed - cfm Second Stage Cooling Speed - cfm
Low Medium-Low Medium-High 2High Low Medium-Low Medium-High 2High
+ 831 969 1103 1269 1096 1323 1541 1731
Factory Default 753 905 1008 1150 1005 1208 1385 1605
– 806 807 932 1045 920 1102 1269 1451
SL297UH080NV60C BLOWER PERFORMANCE (less lter)
BOTTOM RETURN AIR
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1Heating Speed
DIP Switch
Settings
First Stage Heating Speed - cfm Second Stage Heating Speed - cfm
+24% 1591 2135
+18% 1503 2026
+12% 1426 1921
+6% 1334 1828
Factory Default 1277 1716
–6% 1197 1609
–12% 1124 1504
–18% 1037 1402
COOLING
1Cooling Speed
DIP Switch
Settings
First Stage Cooling Speed - cfm Second Stage Cooling Speed - cfm
Low Medium-Low Medium-High 2High Low Medium-Low Medium-High 2High
+ 1094 1253 1388 1580 1584 1825 2065 2286
Factory Default 984 1155 1284 1445 1454 1659 1881 2092
– 868 1021 1152 1302 1301 1490 1693 1890
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specic DIP Switch Settings.
2 Factory default setting.
NOTES - The effect of static pressure is included in air volumes shown.
First stage HEAT is approximately 91% of the same second stage HEAT.
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 selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 450 cfm.
Lennox iHarmony® Zoning System Applications - Minimum blower speed is 250 for 080NV48C and 450 cfm for 080NV60C.

Page 9
BLOWER DATA
SL297UH080NV60C BLOWER PERFORMANCE (less lter)
SINGLE SIDE RETURN AIR - Air volumes in bold require Optional Return Air Base and eld fabricated transition to accommodate
20 x 25 x 1 in. cleanable air lter in order to maintain proper air velocity across the lter.
0 through 0.8 in. w.g. (Heating) and 0 through 1.0 in. w.g. (Cooling) External Static Pressure Range
HEATING
1Heating Speed
DIP Switch
Settings
First Stage Heating Speed - cfm Second Stage Heating Speed - cfm
+24% 1491 2027
+18% 1414 1901
+12% 1351 1801
+6% 1284 1722
Factory Default 1211 1621
–6% 1130 1517
–12% 1048 1407
–18% 993 1323
COOLING
1Cooling Speed
DIP Switch
Settings
First Stage Cooling Speed - cfm Second Stage Cooling Speed - cfm
Low Medium-Low Medium-High 2High Low Medium-Low Medium-High 2High
+ 1094 1279 1430 1609 1599 1823 2051 2239
Factory Default 1003 1160 1308 1454 1438 1649 1863 2097
– 894 1044 1166 1309 1301 1490 1683 1897
1 Cooling and heating speeds are based on a combination of DIP switch settings on the furnace control. Refer to Installation Instructions for specic DIP Switch Settings.
2 Factory default setting.
NOTES - The effect of static pressure is included in air volumes shown.
First stage HEAT is approximately 91% of the same second stage HEAT.
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 selectable at 28%, 38%, 70% and 100% of the selected second stage cooling speed - minimum 450 cfm.
Lennox iHarmony® Zoning System Applications - Minimum blower speed is 450 cfm.

Page 10
FIGURE 1
Heat Exchanger
Gas Valve
Combustion
Air Inducer
Indoor Blower
Two-Stage Control
Cabinet
Panel
Inner Panel
Gas Pipe Inlet
(right side only)
Inlet Vent Pipe
Exhaust Vent Pipe
Exhaust Coupling
Intake Air Assembly
Rollout Switch
Burner Assembly