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Use the following method to determine the firing rate of the furnace. The supply pressure tap should
be located on the field installed piping or gas shut-off valve. The manifold pressure tap is located on
the combination gas valve in the furnace and labeled "PRESSURE TAP".
• Install a manometer graduated in tenths of an inch of water column on the supply pressure tap on
the gas supply pipe.
• Remove the plug at the "Manifold" pressure tap on the gas valve & install a second manometer.
• Determine the size of gas meter used.
• Shut off all other gas fired appliances with the exception of the pilots.
• Adjust the room thermostat.
• Place furnace in operation. The GSM is a two-stage furnace; therefore, both stages are to be
engaged when timing the gas meter.
• Check the supply pressure regulator until the pressure shown on the series and rating plate is
obtained. Adjust if necessary.
• After 15 minutes of operation, time the meter with a stop watch for 2 revolutions and divide by 2.
• Use the appropriate column to determine the furnace input.
• If necessary, adjust the manifold pressure at the gas valve by removing the regulator cap and
turning the adjustment screw clockwise to raise the pressure and counterclockwise to reduce the
pressure. The manifold pressure must be between 3.2" W.C. and 3.8" W.C. for natural gas and 9.5"
W.C. and 10.0" W.C. for L.P.( a field conversion is necessary for L.P.). The inability to obtain the
proper pressure range will require reorificing. After reorificing, repeat the above steps to insure that
the furnace input is adjusted properly.
• Turn off gas and electrical supply, remove manometers and replace any plugs which were removed.
Use a pipe joint compound which is suitable for use with L.P. gas.
• Restore any other appliances affected to their normal operating mode.
METER TIME IN MINUTES AND SECONDS FOR NORMAL INPUT RATING OF FURNACES
EQUIPPED FOR USE WITH NATURAL GAS AT 0 - 2,000 FEET ALTITUDE.
INPUT
METER SIZE
BTU/HR
60,000
80,000
100,000
The main burners do not need adjustment in normal installations.
IO-176
TIMING THE GAS METER
HEAT VALUE
FT3
900
MIN. SEC.
1
0
54
10
9
00
1
0
41
10
6 45
1
0
32
10
5
24
MAIN BURNER ADJUSTMENT
HEAT VALUE
HEAT VALUE
1,000
MIN. SEC.
MIN. SEC.
1
00
1 03
10 00
10
0
45
0
7
30
7
0
36
0
6
00
6
19
HEAT
1040
VALUE
1,100
MIN. SEC.
1
06
24
11
00
47
0
50
48
8
15
37
0
40
14
6
36
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