Repair manual

MT3855
12
CHECKING THE FIRING RATE
Method #1
1. Turn off all other appliances on the line. Press
the ON/OFF key on the unit to call for heat.
2. Using either the 1/2 cu. ft. or the 2 cu. ft. dials,
note the time it takes the indicator to complete
one revolution. See FIGURE 4.
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
determine the firing rate of the apĆ
pliance.
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 4
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.