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Table 4-8
Natural Gas Combustion Curve
(Ratio of Oxygen to Carbon Dioxide in percent)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
0123456789101112131415161718192021
Percent Oxygen
Percent Carbon Dioxide
Curve Fuel
A = 1,000 BTU per cu. ft.
of Natural Gas.
A
Figure 4-8
Gas Valve Adjustment Screw Locations
Table 4-7
Recommended Manifold Pressures and CO
2
Levels
during Furnace Operation (See Notes)
Furnace MBH Firing Manifold
Stage Rate %CO2 Pressure
High-Fire 235 100% 8.5-9.5 3.0-3.5
Low-Fire 117 50% 6.0-7.0 0.9
High-Fire 350 100% 8.5-9.5 3.0-3.5
Low-Fire 175 50% 6.0-7.0 0.9
High-Fire 500 100% 8.5-9.5 3.0-3.5
Low-Fire 250 50% 6.0-7.0 1.25
High-Fire 850 100% 8.5-9.5 3.0-3.5
Low-Fire 500 59% 6.0-7.0 1.25
High-Fire 1000 100% 8.5-9.5 3.0-3.5
Low-Fire 500 50% 6.0-7.0 1.25
Manifold pressures are given in inches w.c.
High fire manifold pressure is adjustable on all heaters.
Low fire manifold pressure is non-adjustable on 235 MBH
and 350 MBH heaters.
Figure 4-7
Flue Gas Carbon Dioxide & Oxygen Measurements