MUA-SVX004B-EN
37
Gas Input Adjustment
When shipped from the factory, all gas fired units are equipped for the average BTU of the gas
stamped on the rating plate.
N
NO
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nsstta
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The input may be checked by either the meter method or the pressure of the gas in the manifold.
A 1/8 inch pipe tap is available on the body of the gas valve.
N
NO
OT
TIIC
CE
E
H
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ea
atte
err D
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D
Do
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au
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un
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y o
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Meter Method of Checking Input
1. Obtain the heating value of the gas from the local utility. This should be in BTU per cubic foot
(MJ/m
3
).
2. Determine the cubic feet per minute of the gas as shown in the following example. The rating
plate input should be taken from the unit as stamped on the plate. EXAMPLE: Assume this is
a unit having an input of 250,000 BTU/hr. and the heating value of the gas to be used in the
furnace is 1000 BTU/hr.
Input =
250,000 BTU/hr.
1000 BTU/cu. ft. x 60 min/hr
= 41.7 cu feet per min.
Before checking the unit input, all other gas appliances connected to the same meter must be
turned off.
3. Fire the unit according to instructions.
4. Observe on the meter dial the cubic feet of gas for a period of five minutes. This should be
41.7 cu ft. per min. x 5 minutes, or 20.8 cu. feet. Minor input adjustments can be made by
moving the regulator screw clockwise for increased input and counter-clockwise for
decreased input. Any appreciable adjustment in input should be made by re-orificing.
Manifold Pressure Method of Checking Input
1. Close the manual gas valve on the unit.
2. Install a 1/8 inch pipe connection in the tapped hold provided on the valve body and a “U”
tube or manometer by means or a rubber hose.
3. Fire the unit and observe the pressure.
4. Small variations in gas pressure adjustment can be made by means of the pressure regulator.
Remove the cap from the regulator. Turning the screw clockwise will increase the input, and
turning it counterclockwise will decrease the input. The adjusted manifold pressure should
not vary more than 10% from the pressures specified in the Main Burner Orifice Schedule
chart in the
Lighting
section of this manual.
