Lennox SLP99UHV Series Installation and operation manual

Page 1
UNIT INFORMATIONUNIT INFORMATION
Service Literature
©2016 Lennox Industries, Inc.
WARNING
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.
WARNING
Electric shock hazard. Can cause injury
or death. Before attempting to perform
any service or maintenance, turn the
electrical power to unit OFF at disconnect
switch(es). Unit may have multiple power
supplies.
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.
SLP99UHV series units are high-e󰀩ciency upow, hori-
zontal right and left) gas furnaces equipped with variable
capacity gas valve, variable speed combustion air inducer
and variable speed indoor blower motor. All models are
designed only for direct vent (dual pipe) venting system.
SLP99UHV units are available in heating capacities from
66,000 to 132,000 Btuh (19.3 to 38.6 kW) and cooling ap-
plications from 2 to 5 tons (7.0 kW to 17.5 kW). Refer to
Engineering Handbook for proper sizing.
Units are factory-equipped for use with natural gas. Kits
are available for conversion to LPG operation. SLP99UHV
models include a SureLight®variable capacity integrated
control that can be used with a Lennox communicating
thermostat as part of a communicating comfort system.
All SLP99UHV units meet the California Nitrogen Oxides
(NOx) Standards and California Seasonal E󰀩ciency re-
quirements.
All specications in this manual are subject to change.
Procedures outlined in this manual are presented as rec-
ommendations 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 con-
stitute code.
TABLE OF CONTENTS
Specications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 2
Optional Accessories . . . . . . . . . . . . . . . . . . . . . . Page 3
Blower Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 4
I Unit Components . . . . . . . . . . . . . . . . . . . . . . . Page 20
II Communicating Thermostat . . . . . . . . . . . . . . Page 44
III Placement and Installation . . . . . . . . . . . . . . Page 47
IV Start Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 63
V Heating System Service Checks . . . . . . . . . . Page 60
VI Typical Operating Characteristics . . . . . . . . Page 69
VII Maintenanc . . . . . . . . . . . . . . . . . . . . . . . . . . Page 71
VIII Wiring and Sequence of Operation . . . . . Page 74
XI Field Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . Page 82
SLP99UHV
100001
10/2021
SLP99UHV SERIES UNITS

Page 2
SPECIFICATIONS
Gas
Heating
Performance
Model No. SLP99UH070XV36B SLP99UH090XV36C SLP99UH090XV48C
1AFUE 98.1% 98.1% 98.2%
Maximum Input - Btuh 66,000 88,000 88,000
Output - Btuh 64,000 85,000 85,000
Temperature rise range - °F 50 - 80 60 - 90 50 - 80
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
3.5 / 10.0 3.5 / 10.0 3.5 / 10.0
Minimum Input - Btuh 23,000 31,000 31,000
Output - Btuh 22,000 30,000 30,000
Temperature rise range - °F 35 - 65 35 - 65 35 - 65
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
0.5 / 1.5 0.5 / 1.5 0.5 / 1.5
High static - in. w.g. 0.8 0.8 0.8
Connections
in.
Intake / ² Exhaust Pipe (PVC) 2 / 2 2 / 2 2 / 2
Gas pipe size IPS 1/2 1/2 1/2
Condensate Drain Trap (PVC pipe) - i.d. 3/4 3/4 3/4
with furnished 90° street elbow 3/4 slip x 3/4 Mipt 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 3/4 slip x 3/4 MPT
Indoor
Blower
Wheel nominal diameter x width - in. 10 x 9 10 x 9 11 x 11
Motor output - hp 1/2 1/2 3/4
Tons of add-on cooling 2 - 3 2 - 3.5 2.5 - 4
Air Volume Range - cfm 339 - 1365 520 - 1360 528 - 1770
Electrical Data Voltage (Maximum Amps) 120 volts - 60 Hertz - 1 phase
Blower motor full load amps 7.7 7.7 10.1
Maximum overcurrent protection 15 15 15
Shipping Data lbs. - 1 package 139 156 166
NOTE - Filters and provisions for mounting are not furnished and must be eld provided.
1 Annual Fuel Utilization E󰀩ciency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces.
22 in. Rubber Flue Coupling is furnished for exhaust pipe connection to unit.
SPECIFICATIONS
Gas
Heating
Performance
Model No. SLP99UH090XV60C SLP99UH110XV60C SLP99UH135XV60D
1AFUE 99% 98.1% 98.4%
Maximum Input - Btuh 88,000 110,000 132,000
Output - Btuh 87,000 106,000 128,000
Temperature rise range - °F 50 - 80 50 - 80 55 - 85
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
3.5 / 10.0 3.5 / 10.0 3.5 / 10.0
Minimum Input - Btuh 31,000 39,000 46,000
Output - Btuh 30,000 38,000 45,000
Temperature rise range - °F 25 - 55 35 - 65 35 - 65
Gas Manifold Pressure (in. w.g.)
Nat. Gas / LPG/Propane
0.5 / 1.5 0.5 / 1.5 0.5 / 1.5
High static - in. w.g. 0.8 0.8 0.8
Connections
in.
Intake / ² Exhaust Pipe (PVC) 2 / 2 2 / 2 2 / 2
Gas pipe size IPS 1/2 1/2 1/2
Condensate Drain Trap (PVC pipe) - i.d. 3/4 3/4 3/4
with furnished 90° street elbow 3/4 slip x 3/4 Mipt 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 3/4 slip x 3/4 MPT
Indoor
Blower
Wheel nominal diameter x width - in. 11 x 11 11 x 11 11 x 11
Motor output - hp 1 1 1
Tons of add-on cooling 3 - 5 3 - 5 3.5 - 5
Air Volume Range - cfm 380 - 2195 580 - 2125 646 - 2190
Electrical Data Voltage (Maximum Amps) 120 volts - 60 Hertz - 1 phase
Blower motor full load amps 12.8 12.8 12.8
Maximum overcurrent protection 20 20 20
Shipping Data lbs. - 1 package 166 176 191
NOTE - Filters and provisions for mounting are not furnished and must be eld provided.
1 Annual Fuel Utilization E󰀩ciency based on DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces.
22 in. Rubber Flue Coupling is furnished for exhaust pipe connection to unit.

Page 3
OPTIONAL ACCESSORIES - ORDER SEPARATELY
NOTE - FURNACES CANNOT BE TWINNED!
“B” Width
Models
“C” Width
Models
“D” Width
Models
CABINET ACCESSORIES
Horizontal Suspension Kit - Horizontal only 51W10 51W10 51W10
Return Air Base - Upow only 50W98 50W99 51W00
High Performance Economizer (Commercial Only) 10U53 10U53 10U53
CONDENSATE DRAIN KITS
Condensate Drain Heat Cable 6 ft. 26K68 26K68 26K68
24 ft. 26K69 26K69 26K69
Crawl Space Vent Drain Kit US 51W18 51W18 51W18
Canada 15Z70 15Z70 15Z70
CONTROLS
iComfort®S30 Ultra-Smart Wi-Fi Thermostat 12U67 12U67 12U67
1Remote Outdoor Air Temperature Sensor X2658 X2658 X2658
Night Service Kit 20F44 20F44 20F44
FILTER KITS
2Air Filter and
Rack Kit
Horizontal (end) 87L96 87L97 87L98
Size of lter - in. 18 x 25 x 1 20 x 25 x 1 25 x 25 x 1
Side Return Single 44J22 44J22 44J22
Ten Pack 66K63 66K63 66K63
Size of lter - in. 16 x 25 x 1 16 x 25 x 1 16 x 25 x 1
TERMINATION KITS
Direct Vent Applications Only. See Installation Instructions for specic venting information.
Direct Vent Concentric US - 2 in. 71M80 69M29 - - -
3 in. - - - 60L46 60L46
Canada - 2 in. 44W92 44W92 - - -
3 in. - - - 44W93 44W93
Flush-Mount US - 2, 2-1/2 or 3 in. 51W11 51W11 51W11
Canada - 2, 2-1/2 or 3 in. 51W12 51W12 51W12
Wall - Close Couple US - 2 in. 22G44 - - - - - -
3 in. 44J40 44J40 44J40
Wall - Close Couple WTK Canada - 2 in. 30G28 - - - - - -
3 in. 81J20 81J20 81J20
Roof Termination Flashing Kit
(no vent pipe - 2 ashings)
2 in. 15F75 15F75 - - -
3 in. 44J41 44J41 44J41
1Remote Outdoor Temperature Sensor is used with conventional (non-iComfort®Communicating) outdoor units (sensor is furnished with iComfort®Communicating
outdoor units). Allows the thermostat to display outdoor temperature. Required in dual-fuel and EDA applications.
2 Cleanable polyurethane frame type lter.
NOTE - Termination Kits (44W92, 44W93, 30G28, 51W12, 81J20) and Crawl Space Vent Drain Kit (15Z70) are certied to ULC S636 standard for use in Canada only.

Page 4
BLOWER DATA
SLP99UH070XV36B BLOWER PERFORMANCE (less lter)
BOTTOM RETURN AIR
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 489 538 636 735 833 931 1030 1128
Increase (+7.5%) Heat CFM 450 496 588 680 772 864 956 1048
Default Heat CFM 410 453 539 624 710 796 881 967
Decrease (-7.5% ) Heat CFM 380 419 498 578 657 736 815 895
Decrease (-15% ) Heat CFM 349 385 458 531 604 676 749 822
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 600 740 840 970 860 1060 1215 1365
Default Cool CFM 555 665 770 855 810 960 1130 1265
Decrease (-10%) Cool CFM 500 600 680 790 705 840 1005 1140
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 250 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 250 cfm.

Page 5
SLP99UH070XV36B BLOWER PERFORMANCE (less lter)
SINGLE SIDE RETURN AIR
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 484 531 625 718 812 906 999 1093
Increase (+7.5%) Heat CFM 446 490 579 667 756 845 933 1022
Default Heat CFM 407 449 533 616 700 784 867 951
Decrease (-7.5% ) Heat CFM 377 413 487 561 635 709 783 857
Decrease (-15% ) Heat CFM 346 378 442 506 571 635 699 763
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 590 705 805 955 840 1050 1205 1355
Default Cool CFM 540 640 725 820 750 945 1130 1230
Decrease (-10%) Cool CFM 500 580 665 720 685 805 990 1110
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 250 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 250 cfm.

Page 6
BLOWER DATA
SLP99UH070XV36B BLOWER PERFORMANCE (less lter)
SINGLE SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 471 519 614 709 805 900 996 1091
Increase (+7.5%) Heat CFM 435 480 570 660 751 841 931 1021
Default Heat CFM 399 441 526 611 696 781 866 951
Decrease (-7.5% ) Heat CFM 369 408 486 564 643 721 799 877
Decrease (-15% ) Heat CFM 339 375 446 517 589 660 732 803
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 595 715 815 950 855 1045 1205 1350
Default Cool CFM 520 655 755 840 790 945 1090 1255
Decrease (-10%) Cool CFM 490 595 670 745 720 845 985 1130
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 250 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 250 cfm.

Page 7
BLOWER DATA
SLP99UH090XV36C BLOWER PERFORMANCE (less lter)
BOTTOM RETURN AIR
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 687 734 827 921 1014 1108 1201 1295
Increase (+7.5%) Heat CFM 654 697 782 867 953 1038 1123 1209
Default Heat CFM 621 660 737 814 891 968 1045 1122
Decrease (-7.5% ) Heat CFM 581 616 687 757 828 899 970 1041
Decrease (-15% ) Heat CFM 540 572 637 701 766 830 895 959
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 625 710 830 950 875 1040 1210 1360
Default Cool CFM 565 670 760 860 800 945 1100 1240
Decrease (-10%) Cool CFM 520 610 685 785 720 840 970 1115
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 250 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 250 cfm.

Page 8
BLOWER DATA
SLP99UH090XV36C BLOWER PERFORMANCE (less lter)
SINGLE SIDE RETURN AIR
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 657 702 792 881 971 1061 1150 1240
Increase (+7.5%) Heat CFM 631 673 757 841 926 1010 1094 1178
Default Heat CFM 605 644 723 802 880 959 1037 1116
Decrease (-7.5% ) Heat CFM 574 608 676 745 814 882 951 1020
Decrease (-15% ) Heat CFM 542 571 630 689 747 806 864 923
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 610 705 795 920 840 1015 1165 1300
Default Cool CFM 560 640 715 810 770 910 1050 1190
Decrease (-10%) Cool CFM 525 605 665 725 695 795 945 1110
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 250 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 250 cfm.

Page 9
BLOWER DATA
SLP99UH090XV36C BLOWER PERFORMANCE (less lter)
SINGLE SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 677 721 810 899 988 1076 1165 1254
Increase (+7.5%) Heat CFM 639 679 760 842 923 1004 1085 1167
Default Heat CFM 600 637 711 784 858 932 1005 1079
Decrease (-7.5% ) Heat CFM 573 606 673 740 806 873 939 1006
Decrease (-15% ) Heat CFM 546 576 635 695 754 814 873 933
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 605 715 810 930 850 995 1165 1305
Default Cool CFM 570 660 735 820 775 905 1050 1205
Decrease (-10%) Cool CFM 530 600 670 725 710 800 945 1070
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 250 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 250 cfm.

Page 10
BLOWER DATA
SLP99UH090XV48C BLOWER PERFORMANCE (less lter)
BOTTOM RETURN AIR
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 769 835 968 1101 1234 1367 1500 1633
Increase (+7.5%) Heat CFM 713 776 902 1028 1155 1281 1407 1534
Default Heat CFM 656 716 836 955 1075 1195 1314 1434
Decrease (-7.5% ) Heat CFM 595 652 767 882 997 1112 1227 1342
Decrease (-15% ) Heat CFM 534 589 699 809 919 1029 1139 1249
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 840 1005 1155 1315 1165 1375 1580 1770
Default Cool CFM 780 915 1045 1190 1075 1265 1440 1645
Decrease (-10%) Cool CFM 690 835 955 1070 935 1145 1320 1465
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 380 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 380 cfm.

Page 11
BLOWER DATA
SLP99UH090XV48C BLOWER PERFORMANCE (less lter)
SINGLE SIDE RETURN AIR
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 747 812 943 1073 1204 1334 1465 1595
Increase (+7.5%) Heat CFM 698 759 882 1005 1127 1250 1372 1495
Default Heat CFM 649 706 821 936 1051 1165 1280 1395
Decrease (-7.5% ) Heat CFM 589 644 755 867 978 1089 1200 1312
Decrease (-15% ) Heat CFM 528 582 690 797 905 1013 1120 1228
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 820 1005 1135 1290 1140 1340 1525 1725
Default Cool CFM 755 880 1025 1150 1040 1235 1395 1565
Decrease (-10%) Cool CFM 680 815 925 1065 910 1120 1275 1400
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 3808 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 380 cfm.

Page 12
BLOWER DATA
SLP99UH090XV48C BLOWER PERFORMANCE (less lter)
SINGLE SIDE RETURN AIR WITH OPTIONAL RETURN AIR BASE
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 764 828 956 1084 1213 1341 1469 1597
Increase (+7.5%) Heat CFM 705 766 888 1010 1132 1255 1377 1499
Default Heat CFM 645 703 819 936 1052 1168 1285 1401
Decrease (-7.5% ) Heat CFM 594 650 762 874 986 1099 1211 1323
Decrease (-15% ) Heat CFM 542 596 704 812 921 1029 1137 1245
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 840 955 1120 1280 1160 1360 1530 1740
Default Cool CFM 775 910 1010 1170 1060 1240 1400 1590
Decrease (-10%) Cool CFM 695 815 930 1045 925 1130 1295 1440
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 380 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 380 cfm.

Page 13
BLOWER DATA
SLP99UH090XV60C BLOWER PERFORMANCE (less lter)
BOTTOM RETURN AIR
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 583 665 830 995 1159 1324 1488 1653
Increase (+7.5%) Heat CFM 540 618 774 930 1085 1241 1397 1553
Default Heat CFM 497 571 718 865 1012 1159 1306 1453
Decrease (-7.5% ) Heat CFM 439 507 644 781 917 1054 1191 1328
Decrease (-15% ) Heat CFM 380 443 570 697 823 950 1076 1203
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 1050 1270 1445 1620 1590 1815 2010 2195
Default Cool CFM 975 1120 1295 1460 1460 1645 1845 2010
Decrease (-10%) Cool CFM 865 1010 1120 1290 1320 1500 1645 1860
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 380 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 450 cfm.

Page 14
BLOWER DATA
SLP99UH090XV60C 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. air lter in order to maintain proper air velocity.
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 609 684 835 986 1136 1287 1437 1588
Increase (+7.5%) Heat CFM 551 623 769 914 1059 1205 1350 1496
Default Heat CFM 492 562 702 842 983 1123 1263 1403
Decrease (-7.5% ) Heat CFM 436 502 633 765 896 1028 1159 1291
Decrease (-15% ) Heat CFM 380 441 564 687 810 932 1055 1178
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 1040 1225 1380 1550 1555 1715 1920 2135
Default Cool CFM 960 1085 1225 1415 1430 1565 1790 1980
Decrease (-10%) Cool CFM 840 990 1085 1250 1280 1450 1580 1790
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 380 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 450 cfm.

Page 15
BLOWER DATA
SLP99UH110XV60C BLOWER PERFORMANCE (less lter)
BOTTOM RETURN AIR
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 767 861 1049 1237 1424 1612 1800 1988
Increase (+7.5%) Heat CFM 738 825 1000 1174 1349 1524 1699 1874
Default Heat CFM 708 789 951 1112 1274 1436 1597 1759
Decrease (-7.5% ) Heat CFM 655 731 883 1035 1187 1339 1491 1644
Decrease (-15% ) Heat CFM 602 673 816 958 1101 1243 1386 1528
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 1060 1245 1345 1545 1560 1740 1930 2125
Default Cool CFM 970 1145 1265 1395 1405 1565 1775 1945
Decrease (-10%) Cool CFM 885 1025 1110 1250 1270 1425 1610 1770
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 380 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 450 cfm.

Page 16
BLOWER DATA
SLP99UH110XV60C 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. air lter in order to maintain proper air velocity.
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 733 825 1009 1194 1378 1562 1747 1931
Increase (+7.5%) Heat CFM 708 794 967 1139 1312 1484 1657 1829
Default Heat CFM 683 763 924 1085 1245 1406 1566 1727
Decrease (-7.5% ) Heat CFM 632 707 857 1007 1157 1307 1457 1608
Decrease (-15% ) Heat CFM 580 650 790 929 1069 1209 1348 1488
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 1050 1195 1315 1495 1515 1710 1870 2065
Default Cool CFM 960 1095 1220 1355 1360 1555 1755 1890
Decrease (-10%) Cool CFM 850 985 1095 1220 1215 1400 1555 1755
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 380 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 450 cfm.

Page 17
BLOWER DATA
SLP99UH135XV60D BLOWER PERFORMANCE (less lter)
BOTTOM RETURN AIR
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 949 1033 1200 1367 1534 1701 1868 2035
Increase (+7.5%) Heat CFM 879 957 1113 1269 1426 1582 1738 1895
Default Heat CFM 808 881 1026 1172 1317 1463 1608 1754
Decrease (-7.5% ) Heat CFM 748 817 956 1095 1235 1374 1513 1652
Decrease (-15% ) Heat CFM 687 753 886 1019 1152 1284 1417 1550
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 1070 1260 1410 1555 1565 1750 1970 2190
Default Cool CFM 980 1115 1255 1430 1445 1615 1805 1985
Decrease (-10%) Cool CFM 865 1020 1115 1280 1290 1470 1650 1805
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 380 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 450 cfm.

Page 18
BLOWER DATA
SLP99UH135XV60D 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. air lter in order to maintain proper air velocity.
HEATING BLOWER PERFORMANCE - 0 through 0.8 in. w.g. External Static Pressure Range
Heating Adjust CFM Selections Heating Input Range and Blower Volume - CFM
35% 40% 50% 60% 70% 80% 90% 100%
Increase (+15%) Heat CFM 927 1010 1175 1340 1505 1671 1836 2001
Increase (+7.5%) Heat CFM 844 923 1081 1239 1398 1556 1714 1873
Default Heat CFM 760 836 987 1138 1290 1441 1593 1744
Decrease (-7.5% ) Heat CFM 703 775 919 1064 1208 1352 1496 1641
Decrease (-15% ) Heat CFM 646 715 852 989 1126 1263 1400 1537
COOLING BLOWER PERFORMANCE - 0 through 1.0 in. w.g. External Static Pressure Range
Cooling Adjust CFM
Selections
Blower Speed Selections
First Stage Cool Speed - cfm Second Stage Cool Speed - cfm
Low Medium-
Low
Medium
High
High
(Default)
Low Medium-
Low
Medium
High
High
(Default)
Increase (+10%) Cool CFM 1070 1235 1385 1535 1550 1720 1925 2005
Default Cool CFM 985 1110 1245 1395 1415 1605 1755 1970
Decrease (-10%) Cool CFM 870 1010 1110 1260 1280 1435 1610 1755
The e󰀨ect of static pressure is included in air volumes shown.
The following control congurations are available. See Installation Instructions for details and DIP switch settings.
Heat Modes Available (Heating Blower Performance Table):
Single stage thermostat:
- 35%, 70%, 100% input (three-stage) with time delays in-between.
Two-stage thermostat:
- Variable Rate Capacity Mode - furnace automatically adjusts ring rate based on rst- and second-stage cycle times.
- W1 demand at 70% input, W2 demand at 100% input. No delay between stages.
Cool Mode Available (Cooling Blower Performance table):
First stage COOL (two-stage air conditioning units only) is approximately 70% of the same second stage COOL speed position.
Continuous Fan speeds are approximately 28% and 38% (DIP switch selectable) of the same second-stage COOL speed position.
minimum 380 cfm.
Lennox iHarmony®Zoning System Applications - Minimum blower speed is 450 cfm.

Page 19
BURNER BOX ASSEMBLY
VARIABLE
CAPACITY
GAS VALVE
HEAT EXCHANGER
A
CCESS PANEL
CONTROL BOX
(includes variable capacity integrated control
transformer, circuit breaker and door switch)
VARIABLE SPEED BLOWER MOTOR
BAG ASSEMBLIES
(shipping location)
COLD END HEADER
BOX
PRESSURE SWITCHES
VARIABLE SPEED
COMBUSTION AIR
INDUCER
INNER BLOWER
ACCESS PANEL
SIGHT GLASS
PRIMARY LIMIT
SHIPPING BLOCK
(-135 UNITS ONLY)
FIGURE 1

Page 20
I-UNIT COMPONENTS
SLP99UHV unit components are shown in FIGURE 1. The
gas valve, combustion air inducer and burners can be ac-
cessed by removing the access panel. Electrical compo-
nents are in the control box (FIGURE 2) found in the blow-
er compartment. SLP99UHV units are factory-equipped
with a bottom return air panel in place. The panel is de-
signed to be eld removed as required for bottom air re-
turn. Markings are provided for side return air and may be
cut out in the eld.
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
CAUTION
Electrostatic discharge can a󰀨ect
electronic components. Take precautions
to neutralize electrostatic charge by
touching your hand and tools to metal
prior to handling the control.
A-Control Box
1. Control Transformer (T1)
A transformer located in the control box provides power
to the low voltage section of the unit. Transformers on all
models are rated 40VA with a 120V primary and a 24V
secondary.
2. Interlock Switch (S51)
An interlock switch rated 14A at 125VAC is wired in series
with line voltage. When the inner blower access panel is
removed the unit will shut down.
CONTROL BOX
SURELIGHT®
INTEGRATED
CONTROL
TRANSFORMER
CIRCUIT
BREAKER
INTERLOCK
SWITCH
FIGURE 2
3. Circuit Breaker (CB8)
A 24V circuit breaker is also located in the control box. The
switch provides overcurrent protection to the transformer
(T1). The breaker is rated 3A at 32V. If the current exceeds
this limit the breaker will trip and all unit operation will shut
down. The breaker can be manually reset by pressing the
button on the face. See FIGURE 3.
CIRCUIT BREAKER CB8
PRESS TO RESET
FIGURE 3
WARNING
Shock hazard. Disconnect power before
servicing. Integrated control is not eld
repairable. If control is inoperable, simply
replace entire control. Can cause injury
or death. Unsafe operation will resul if
repair is attempted.
4. Integrated Control (A92)
SLP99UHV units are equipped with the Lennox SureLight®
variable-capacity integrated control. This control can be
used with the icomfort Wi-Fi®thermostat as part of a com-
municating comfort system. The control can also operate
with a conventional single or two-stage thermostat. The
system consists of an ignition / blower control (FIGURE 4
and FIGURE 5) with control pin designations in TABLE 1
and TABLE 2, and ignitor.
The control provides gas ignition, safety checks and in-
door blower control with variable capacity rate gas heat-
ing. The furnace combustion air inducer, gas valve and in-
door blower are controlled in response to various system
inputs such as thermostat signal, pressure and limit switch
signal and ame signal. The control features a seven-seg-
ment LED display, indicating furnace status (including in-
door blower) and error codes. The LED ashes in single
digits. For example using table 14 under LIMIT CODE, an
“E” followed by “2” followed by “5” followed by “0”, the limit
switch circuit is open. The control also has two 120 volt
accessory terminals (used for a humidier and electronic
air cleaner) rated at (1) one amp each.