Instructions / Assembly

21
Checking the Input of the Furnace
Refer to the furnace rating plate to determine the fi ring
rate of the furnace. Using Table 4 (page 19), determine
the appropriate orifi ce size for the fi ring rate and gas
being used in your application. Check the burner orifi ce to
ensure that it is the correct size.
The input of this furnace
can be checked using the following steps:
1. Shut off all other gas fi red appliances.
2. Start the furnace run it for at least 3 minutes.
3. Measure the time (in seconds) required for the
gas meter to complete one revolution. NOTE: One
revolution equals 1 cubic foot of gas.
4. Compare the time measured with the appropriate
time listed in Table 4 (page 16). If the time varies by
more that 5% from the times shown in the table, then
measure the inlet and gas valve manifold pressures.
See Checking the Inlet Gas Pressure and Checking
the Manifold Pressures sections below.
WARNING:
Do not attempt to drill the gas orifi ces. Use only
factory supplied orifi ces. Improperly drilled
orifi ces may cause fi re, explosion, carbon
monoxide poisoning, personal injury or death.
5. If the inlet gas pressure and the manifold pressure
are both properly set, then check the burner orifi ce to
ensure that it is properly sized. Further gas problems
should be referred to the local gas supplier.
Checking the Inlet Gas Line Pressure
The inlet gas line pressure can be checked at the port
located on the inlet end of the gas valve. See Installing
the Pressure Gauge or U-Tube Manometer section.
• Natural gas installations: The inlet gas line pressure
at the gas valve must be between 5 in. W.C. & 7 in. W.C.
• LP gas installations: The inlet gas line pressure at the
gas valve must be between 11 in. W.C. & 13 in. W.C.
Checking the Manifold Pressure
The manifold pressure can be checked at the port located
on the gas outlet end of the gas valve using a pressure
gauge or U-tube manometer. If the manifold pressure is
not equal to the values below, then it must be adjusted.
See Installing the Pressure Gauge or U-Tube Manometer.
• Natural gas installations: The manifold pressure must
be set at 3.5 in. W.C.
• LP gas installations: The manifold pressure must be
set at 10.0 in. W.C.
Adjusting the Manifold Pressure
1. Remove the regulator converter from the gas valve,
See Figure 14.
2. Turn the adjusting screw clockwise to increase the
pressure or counterclockwise to reduce the pressure.
3. After setting the manifold pressure, replace the
regulator converter in the same manner it was removed
earlier.
Installing the Pressure Gauge or U-Tube Manometer
1. Determine which type of pressure (inlet gas or manifold
pressure) needs to be measured.
2. Using a 3/16” Allen wrench, remove the appropriate
tap plug located on the gas valve. See Figure 14.
NOTE: To measure the inlet gas pressure, remove the
tap plug on the inlet side of the gas valve. To measure
the manifold pressure, remove the tap plug on the
outlet side of the gas valve.
3. Install a fi tting that has a 1/8” NPT pipe thread and
is compatible with the pressure gauge or U-tube
manometer on the valve.
4. Connect the pressure gauge or U-tube manometer
to the gas valve. Refer to the gauge manufacturer’s
supplied instructions for proper hookup and usage.
5. After measuring the pressure, remove the pressure
gauge or U-tube manometer from the gas valve and
replace the tap plug. NOTE: Make sure the tap plug
is tight and isn’t cross-threaded.
INLET
TA P
OUTLET
TA P
Regulator
Converter
Figure 14. Direct Ignition Gas Valve
Adjusting the Burner
The air shutter of the gas gun burner is pre-set at the
factory and should not be adjusted unless the fi ring rate
of the furnace needs to be converted. The burner should
run quietly. Verify the air shutter setting is correct as
shown in Table 7. NOTE: It is very important that there
is an ample supply of combustion air without decreasing
burner effi ciency. An inadequate amount of fresh air can
cause carbon monoxide (CO) production. The carbon
dioxide (CO
2) content of the fl ue products should be in
the range of 8.0% to 9.0% for natural gas and 9.0% to
10.0% for LP gas.
Table 7. Air Shutter Setting for Different Fuels
Input
(BTU/H)
Natural
Gas Setting
LP Gas
Setting
Oil Setting
65,000 3.7 3.75 3.75
75,000 4.5 4.5 4.0
85,000 5.5 5.5 5.0