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Proper Combustion
Furnace should operate minimum 15 minutes with correct
manifold pressure and gas flow rate before checking
combustion. Take combustion sample beyond the flue outlet
and compare to the tables below. The maximum carbon
monoxide reading should not exceed 100 ppm.
Unit
CO
All
7.6 - 8.6
Table 26. High Fire
Unit
CO
070
090
110
5.3 - 6.3
135
Table 27. Low Fire
Manifold Pressure Nat Gas
Firing
Rate
Min
40%
0.5
70%
1.7
100%
3.2
NOTE: A natural to LP/propane gas changeover kit (Figure 45) is necessary to convert this unit. Refer to the changeover kit
installation instructions for the conversion procedure.
Table 28. Manifold and Operating Signal Pressures in inches 0-7500 ft (0-2286 m)
LP/Propane
Kit
Unit
0 - 10,000
(0 - 3048 m)
070
090
68W77
110
135
NOTE: The values given are measurements only. The gas valve should not be adjusted.
Table 29. Conversion Kit Requirements and Manifold Test Pressures
31-5000723 Rev. 0
% for Nat
CO
% for L.P.
2
2
9.1 - 10.1
% for Nat
CO
% for L.P.
2
2
5.7
7.2 - 8.2
6.8 - 7.8
Normal
Max
0.6
0.7
1.9
2.1
3.5
3.8
High Altitude Pressure
Switch Kit
0 - 7,500
7,501 - 10,000
(0 - 2286 m)
(2287 - 3048 m)
Not required
14T65
High Altitude
NOTE: In Canada, certification for installations at elevations
over 4500 feet (1372 m) is the jurisdiction of local authorities.
NF97UM units require no manifold pressure adjustments
for operation at altitudes up to 10,000 feet (3048m) above
sea level. Units installed at altitude of 7,501 to 10,000 feet
(2287 to 3048m) require a pressure switch change per Table
29. Table 29 also lists gas conversion kit requirements at all
altitudes.
The combustion air pressure switch is factory-set and
requires no adjustment.
Manifold Pressure LP/Propane
Min
Normal
Max
1.3
1.6
1.9
5.1
5.5
5.9
9.5
10.0
10.5
Manifold Pressure at All Altitudes (in. w.g.)
Low Fire
(35% rate)
Natural
LP/
Gas
Propane
0.40 - 0.60
1.2 - 1.8
Page 57
Operating Pressure Signal (Delta P)
Min
Normal
0.25
0.30
0.60
0.65
1.10
1.15
High Fire
(100% rate)
Natural
LP/Propane
Nat
Gas
3.2 - 3.8
9.5 - 10.5
.0625
Max
0.35
0.70
1.20
Gas Orifice
Size
LP
.034
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