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Table 55. Recommended manifold pressures and O2 levels for furnace operation — natural gas (continued)
Burner size
Low Fire (1%) High Fire (100%)
O2 (%)
Manifold
(in. w.c)
O2 (%)
Manifold
(in. w.c)
1000 MBH 2-stg
4.9 – 5.1 0.65 – 0.67 2.8 – 3.2 2.5 – 2.7
1000 MBH Mod 11.2 – 11.4 0.01 – 0.02 2.8 – 3.2 2.5 – 2.6
Note: If the manifold pressure is not within the range shown on the chart, then the combustion fan speeds (P0, P1, and/or P2) need
adjustment. Typically, in increments of 20-40 RPM
(a)
800MBH is Horizontal Discharge. MBH is listed on gas heat rating plate.
Table 56. Recommended manifold pressures and O2 levels for furnace operation — LP
Burner size
Low Fire (1%) High Fire (100%)
O2 (%)
Manifold
(in. w.c)
O2 (%)
Manifold
(in. w.c)
235 MBH 2-stg
5.2 - 5.6 0.14 - 0.18 3.1 - 3.4 0.67 - 0.69
350 MBH 2-stg
6.4 - 6.7 0.12 - 0.14 3.2 - 3.4 0.43 - 0.53
500 MBH 2-stg
5.4 - 5.8 0.2 - 0.3 3.0 - 3.4 0.9 - 1.0
500 MBH Mod 10.4 - 10.8 0.05 - 0.08 3.1 - 3.5 0.9 - 1.1
800 MBH 2-stg
(a)
5.4 - 5.8 0.14 - 0.15 2.9 - 3.3 0.62 - 0.64
800 MBH Mod
(a)
12.8 - 13.1 0 - 0.01 3.0 - 3.4 0.62 - 0.65
850 MBH 2-stg
5.7 - 6.1 0.16 - 0.17 6.2 - 3.4 0.70 - 0.73
850 MBH Mod 12.7 - 13.1 0 - 0.01 3.2 - 3.4 0.68 - 0.72
1000 MBH 2-stg
5.2 - 5.5 0.25 - 0.27 3.0 - 3.4 0.92 - 0.96
1000 MBH Mod 12.8 - 13.2 0 - 0.01 2.9 - 3.3 0.92 - 0.96
Note: If the manifold pressure is not within the range shown on the chart, then the combustion fan speeds (P0, P1, and/or P2) need
adjustment. Typically, in increments of 20-40 RPM
(a)
800MBH is Horizontal Discharge. MBH is listed on gas heat rating plate.
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