20
Check the Furnace Input Rate
(if required)
IMPORTANT:
■
The furnace input rate must not exceed the input rating on
the furnace rating plate.
■
This furnace is equipped for rated input at manifold pressures
of 1.7" (4.32 cm) W.C. (1
st
stage) and 3.5" (8.89 cm) W.C.
(2
nd
stage) for Natural gas. When an LP conversion kit is used,
it is equipped for rated input at manifold pressures of 4.9"
(12.45 cm) W.C. (1
st
stage) and 10.0" (25.4 cm) W.C.
(2
nd
stage) for propane gas.
■
For natural gas, check the furnace rate by observing the gas
meter, making sure all other gas appliances are turned off.
The test hand on the meter should be timed for at least one
revolution.
■
At altitudes from 2,000 to 7,500 ft (609.6 m to 2,286 m) the
furnace input rate must not exceed that on the rating plate.
NOTE: The actual heating value of your gas can be obtained from
your local utility company. Typical values are shown in the
Manifold Pressure vs. Altitude Chart in “Adjust the Furnace Input
Rate.”
Adjust the Furnace Input Rate
(if required)
For Altitudes 4,500 to 7,500 ft (1,371.6 m to 2,286 m)
Above Sea Level
1. Remove the burner access door.
2. Turn the gas control to the OFF position. Use only your hand
to move the gas control; tools are not required.
3. Remove the outlet pressure tap plug on the gas control valve
and connect pressure gauge to the
¹⁄₈
" (3.2 mm) NPT outlet
pressure tap.
Gas Control Valve
4. Be sure the gas control has been in the OFF position for at
least 5 minutes before starting the unit.
5. Move the gas control to the ON position.
NOTE: This furnace is equipped with an ignition device which
automatically lights the burner. This furnace cannot be lighted
manually. Do not try to light the burner by hand.
6. Turn on the electrical power to the furnace.
7. Set the room thermostat to a point above room temperature
to light the main burners.
8. Observe the pressure reading on the pressure gauge.
9. Refer to the Manifold Pressure vs. Altitude Chart later in this
section for the correct manifold pressure. If necessary, turn
the regulator adjusting screw clockwise to increase pressure
and input, or counterclockwise to decrease pressure and
input.
NOTE: The pressure regulator adjustment is sensitive; one
turn of the adjusting screw will result in a large change in
manifold pressure.
IMPORTANT: If the manifold pressure cannot be adjusted to
the correct value, contact your gas supplier.
10. Move the gas control to the OFF position.
11. Disconnect the pressure gauge from the
¹⁄₈
" NPT outlet
pressure tap.
12. Replace outlet pressure tap plug and the regulator adjusting
cap on the gas control valve.
13. Move the gas control to the ON position.
14. Replace the burner access door.
15. Set the room thermostat to the desired temperature
necessary to achieve optimum temperature rise.
For Altitudes 7,500 to 10,000 ft (2,286 m to 3,048 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).
Btu/h
Input
=
Cu. ft per Revolution
x 3600 x Heating
Value
# Seconds per Revolution
A. Regulator adjusting cap
B.
¹⁄₈
" (3.2 mm) NPT outlet
pressure tap
C.
¹⁄₂
" (1.3 cm) NPT outlet
D. Gas control
E. Alternate gas control
F.
¹⁄₈
" (3.2 mm) NPT inlet pressure tap
G.
¹⁄₂
" (1.3 cm) NPT inlet
OFF
ON
F
A
B
D
G
C
E
Manifold Pressure vs. Altitude Chart for Natural Gas
Altitude—ft (m)
Heating Value
(Btu/ft
3
)
Manifold
Pressure
(in. W.C.)
Input
Factor
2,000 (609.6)
948
3.5
0.9666
3,000 (914.4)
914
3.5
0.9499
4,000 (1,219.2)
881
3.5
0.9332
4,500 (1,371.6)
865
3.5
0.9249
5,000 (1,524)
849
3.29
0.89
5,500 (1,676.4)
833
3.27
0.879
6,000 (1,828.8)
818
3.25
0.868
6,500 (1,981.2)
802
3.23
0.857
7,000 (2,133.6)
787
3.21
0.846
7,500 (2,286)
771
3.19
0.835
