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Manifold Pressure vs. Altitude Chart—
Models WFAR, WFAT, WFLU, WFLR, WFLT Only
Natural Gas
Heating Value
Altitude—ft (m)
(Btu/ft
2,000 (609.6)
948
3,000 (914.4)
914
4,000 (1,219.2)
881
4,500 (1,371.6)
865
5,000 (1,524)
849
5,500 (1,676.4)
833
6,000 (1,828.8)
818
6,500 (1,981.2)
802
7,000 (2,133.6)
787
7,500 (2,286)
771
IMPORTANT: Do not use this furnace if any part has been under
water. Immediately call a qualified person to inspect the furnace
and to replace any part of the control system and gas control
which has been under water.
1. Check that you have all of your tools.
2. Dispose of/recycle all packaging materials.
3. Check the furnace in its final location. Be sure the vent is not
blocked.
Measure Temperature Rise
1. Adjust room thermostat to the highest temperature setting
possible.
2. After 20 minutes of heating operation, measure the furnace
temperature rise. Take air temperature readings in both the
return air ducts and the heated air ducts (about 72"
[182.9 cm] from the furnace where they will not be affected by
radiant heat) as shown.
NOTE: If more than one run of return or heated air ducts are
used, air temperature measurements should be taken in each
duct. These measurements can be converted to an average
to obtain the temperature rise of the whole system.
18
Manifold
Pressure—
Input
3
)
W.C.
Factor
in. (cm)
3.5 (8.89)
0.9666
3.5 (8.89)
0.9499
3.5 (8.89)
0.9332
3.5 (8.89)
0.9249
3.29 (8.36)
0.8900
3.27 (8.31)
0.8790
3.25 (8.25)
0.8680
3.23 (8.2)
0.8570
3.21 (8.15)
0.8460
3.19 (8.1)
0.8350
Complete Installation
Manifold Pressure vs. Altitude Chart—
Model WFAU 150 only
Natural Gas
Heating Value
Altitude—ft (m)
(Btu/ft
2,000 (609.6)
948
3,000 (914.4)
914
4,000 (1,219.2)
881
4,500 (1,371.6)
865
5,000 (1,524)
849
5,500 (1,676.4)
833
6,000 (1,828.8)
818
6,500 (1,981.2)
802
7,000 (2,133.6)
787
7,500 (2,286)
771
For Altitudes 7,500 to 10,000 ft (1,371.6 m to 2,286 m)
Above Sea Level
Do not adjust manifold pressure. An orifice change is required.
For the correct orifice size, see Table F.4 in Appendix F of the
National Fuel Gas Code (ANSI Z223.1/NFPA 54, latest edition).
B
A
D
A. Measure return air here.
B. Warm air
3. If furnace doesn't maintain temperature rise within the range
shown on the furnace rating plate, adjust the blower speed.
Manifold
Pressure—
Input
3
)
W.C.
Factor
in. (cm)
3.41 (8.66)
0.9666
3.41 (8.66)
0.9499
3.41 (8.66)
0.9332
3.41 (8.66)
0.9249
3.2 (8.13)
0.8900
3.18 (8.08)
0.8790
3.16 (8.03)
0.8680
3.14 (7.98)
0.8570
3.12 (7.92)
0.8460
3.11 (7.9)
0.8350
C
C. Measure supply temperature here.
D. Return air
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