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TABLE 29 
Manifold and Operating Signal Pressures in inches 0 - 7500 ft (0 - 2286 m)
SLP99 Firing 
Rate
Manifold Pressure Natural Gas Manifold Pressure LP/Propane Operating Pressure Signal (Delta P)
Min Max Min Max Min Max
Low 0.40 0.95 1.2 2.8 0.20 0.40
High 3.0 3.8 9.1 10.5 0.95 1.25
-090-060C Only Min Max Min Max Min Max
Low 0.30 0.85 ---- ---- 0.15 0.35
Low ---- ---- 1.2 2.8 0.20 0.40
High 3.0 3.8 9.1 10.5 0.95 1.25
NOTE - A natural to LP/propane gas changeover kit is necessary to convert this unit. Refer to the changeover kit 
installation instruction for the conversion procedure.
Proper Combustion
Furnace should operate a minimum of 15 minutes with 
correct manifold pressure and gas ow rate before check-
ing combustion. Take combustion sample beyond the ue 
outlet and compare to the tables below. The maximum 
carbon monoxide reading should not exceed 100 ppm.
TABLE 30 
High Fire
Model Input Size CO2% Nat CO2% LP
070
6.5 - 9.0 7.7 - 10.2
090
110
135
TABLE 31 
Low Fire
Model Input Size CO2% Nat CO2% LP
070
4.7 - 7.2 5.7 - 8.2
090
110
135
High Altitude Information
NOTE - In Canada, certication for installations at eleva-
tions  over  4500  feet  (1372  m)  is the  jurisdiction of  local 
authorities.SLP99UHV units require no manifold pressure 
adjustments for operation at altitudes up to 10,000 feet 
(3048 m) above sea level. Units installed at altitude of 
7,501 to 10,000 feet (2287 to 3048m) require a pressure 
switch change and conversion kit. See TABLE 32.
The combustion air pressure switch is factory-set and re-
quires no adjustment.
TABLE 32 
Conversion Kit & High Altitude Requirements
Model Input
LP/Propane Conversion Kit
Natural Burner 
Kit
0 - 4500 ft 
(0 - 1372m)
4501 - 10,000 ft 
(1372  3048m)
4501 - 10,000 ft 
(1372  3048m)
070
65W77 65W77 Not Required
090XV36C/48C
090XV60C 20A26 20A88 20A89
110
65W77 65W77 Not Required
135
Model Input
High Altitude Pressure Switch
0 - 7500 ft
(0 - 2286m)
7501 - 10,000 ft 
(2286 - 3048m)
070
Not 
Required
14T65
090XV36C/48C
090XV60C 20A87
110
14T65
135
Other Unit Adjustments
Primary Limit
The primary limit is located on the heating compartment 
vestibule panel. This limit is factory set and require no ad-
justment.
Flame Rollout Switches (Two)
These manually reset switches are located on the inside 
of the burner box. If tripped, check for adequate combus-
tion air before resetting.