Repair manual

CALIBRATION AND ADJUSTMENT
4-16
CHECKING THE FIRING RATE
Method #1
1. Turn off all other appliances on the line. Turn on
the appliance to be measured.
2. Using either the 1/2 cu. ft. or the 2 cu. ft. dials
located on the gas meter, note the time it takes
the indicator to complete one revolution. See
FIGURE 10.
3. Use the following formula to determine the firĆ
ing rate of the meter.
3600 x size of test dial x 1000
# of seconds per revolution
=ĂBTU/burner
Example:
A.) 3600 x 2 = 7200
B.)
7200
60
=Ă120 Cu. Ft./Hr
C.) To convert to BTU/Hr, multiply by one of the
following generally accepted heating valĆ
ues:
Natural Gas - 1000 x 120 = 120,000 BTU
Propane - 2550 x 120 = 306,000 BTU
Butane - 3000 x 120 = 360,000 BTU
NOTE: You may also use TABLE XII from the
National Fuel Gas Code Handbook to
aid in determining the firing rate of the
appliance. This table eliminates the
use of the formulas above.
Locate the time observed in STEP 2. Move
across the table to either the 1/2 cu. ft. or the
2 cu. ft. column to find the gas input to the
burner.
0
9
8
7
6
5
4
3
2
1
0
9
8
7
6
5
4
3
2
1
0
9
8
7
6
5
4
3
2
1
0
9
8
7
6
5
4
3
2
1
100 THOUSAND 10 THOUSAND 1 THOUSAND1 MILLION
TWO
FEET
HALF
FOOT
CUBIC FEET
TYPICAL DOMESTIC GAS METER INDEX
FIGURE 10
Method #2
You may also determine the firing rate by sizing the
main burner orifice and measuring manifold gas
pressure. Either way is accurate, however method
#1 is faster.