GC9C80 Service Manual
SCHEDULED MAINTENANCE
24
5. Use this formula to verify the Cubic Feet per Hour (CFH) input determined in step 4 is correct:
(3600 x Gas Meter Dial Size) / Time (seconds) = Cubic Feet per Hour (CFH)
3600 is used as there are 60 seconds in
a minute and 60 minutes in an hour.
60x60=3600
6. Check with your local utility for actual BTU content (caloric value) of natural gas in the area (the average is 1025
BTU’s).
7. Use this formula to calculate the BTU/HR input (See BTU/HR Calculation Example):
8. Should the gure you calculated not fall within ve (5) percent of the nameplate rating of the unit, adjust the gas valve
pressure regulator or resize orices. To adjust the pressure regulator on the gas valve, turn downward (clockwise) to
increase pressure and input, and upward (counterclockwise) to decrease pressure and input. A properly operating unit
must have the BTU per hour input and CFM of air, within the limits shown to prevent short cycling of the equipment. As
the external static pressure goes up, the temperature rise will also increase. Consult the proper tables for temperature
rise limitation.
The unit being tested takes 40 seconds for the 1 cubic foot dial to make one complete revolution. Using the chart, this
translates to 90 cubic feet per hour. Based upon the assumption that one cubic foot of natural gas has 1,025 BTU’s (Check
with your local utility for actual BTU content), the
90,000 BTU/HR
92,250 BTU/HR