43
ADJUSTING OR CHECKING FURNACE INPUT
The maximum gas supply pressure to the furnace should be
10 .5” w .c . for natural gas and 13 .0” w .c . for L .P . The minimum
gas supply pressure for purposes of input adjustment to the fur-
nace should be 5” w .c . for natural gas and 11 .0” w .c . for L .P .
A calibrated manometer is required for accurate gas pressure
readings .
The manifold pressure should be set at 3 .5” w .c . for natural
gas and 10 .0” w .c . for L .P . Only small variations in the gas flow
should be made by means of the pressure regulator adjustment .
In no case should the final manifold pressure vary more than
plus or minus 0 .3” w .c . from the above- specified pressures . To
adjust the pressure regulator, remove the regulator cap and turn
the adjustment screw clockwise to increase pressure or coun-
terclockwise to decrease pressure . Then replace the regulator
cap securely . Any necessary major changes in the gas flow rate
should be made by changing the size of the burner orifices .
To change orifice spuds, shut off the manual gas valve and re-
move the gas manifold . On LP gas furnaces, the LP gas supply
pressure must be set between 11” and 13” w .c . by means of the
tank or branch supply regulators . The furnace manifold pressure
should be set at 10” w .c . at the gas control valve . For eleva-
tions up to 2,000 feet, rating plate input ratings apply . For high
altitudes (elevations over 2,000 ft .), see conversion kit index for
derating and orifice spud sizes .
Checking furnace input is important to prevent over firing be-
yond its design-rated input . NEVER SET INPUT ABOVE THAT
SHOWN ON THE RATING PLATE . Use the following table or
formula to determine input rate . Start the furnace and measure
the time required to burn one cubic foot of gas . Prior to checking
the furnace input, make certain that all other gas appliances are
shut off, with the exception of pilot burners . Time the meter with
only the furnace in operation . See Table 11 .
TABLE 10
TIMING DIAGRAM
ST-A1194-27-X0
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OPEN
OFF
OFF
CLOSED
OPEN
ON
ON
ON
ON
ON
ON
OFF
ON
TIMING DIAGRAM, FIELD SELECTIONS &
ADJUSTMENTS
Field Selections
Summary of Contents for 801C Series
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