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b. Check gas input rate by clocking gas meter.
(1.) Obtain average yearly heat value for local gas
supply.
(2.) Check and verify orifice size in furnace. NEVER
ASSUME THE ORIFICE SIZE. ALWAYS
CHECK AND VERIFY.
CAUTION: DO NOT redrill burner orifices. Improper
drilling (burrs, out of round, etc.) can cause excessive
burner operating noise and misdirection of burner flames.
This could result in flame impingement on burners and
heat exchanger surfaces, leading to potential failures.
(3.) Turn off all other gas appliances and pilots.
(4.) Start furnace and let run for 3 minutes.
(5.) Measure time (in sec) for gas meter to complete 1
revolution.
(6.) Refer to Table 7 for cu ft of gas per hr.
(7.) Multiply gas rate (cu ft/hr) by heating value (Btu/cu
ft).
EXAMPLE:
Btu heating input = Btu/cu ft X cu ft/hr
Heating value of gas = 1070 Btu/cu ft
Time for 1 revolution of 2 cu ft dial = 72 sec
Gas rate = 100 X 1070 = 107,000 Btuh
(8.) Measured gas input should not exceed gas input on
unit rating plate.
(9.) Proceed to item c to adjust manifold pressure.
c. Adjust gas input.
(1.) Remove regulator adjustment seal cap. (See Fig.
12.)
(2.) Turn adjusting screw counterclockwise to decrease
input. Turn screw clockwise to increase input. DO
NOT set manifold pressure less than 3.2-in. wc or
more than 3.8-in. wc for natural gas. Make any
major adjustments by changing main burner ori-
fices.
TABLE 6—MODEL 395CAV ORIFICE SIZE AND MANIFOLD PRESSURE FOR CORRECT INPUT RATE
(Tabulated Data Based on Altitude Up to 2000 Ft and 22,000 Btuh Per Burner)
GAS
HEAT
VALUE
(BTU/CU FT)
SPECIFIC GRAVITY OF NATURAL GAS
0.56 0.58 0.60 0.62 0.64 0.66 0.68 0.70 0.72
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
860
41
42
—
3.2
3.6
—
41
42
—
3.3
3.7
—
41
42
40
3.4
3.8
3.2
41
40
—
3.5
3.3
—
41
39
40
3.7
3.2
3.4
41
39
40
3.8
3.3
3.5
39
40
—
3.4
3.6
—
38
39
40
3.2
3.5
3.7
38
39
40
3.3
3.6
3.8
875
42
—
—
3.4
—
—
41
42
—
3.2
3.6
—
41
42
—
3.3
3.7
—
41
42
40
3.4
3.8
3.2
41
40
—
3.5
3.3
—
41
39
40
3.6
3.2
3.4
41
39
40
3.8
3.3
3.5
39
40
—
3.3
3.6
—
38
39
40
3.2
3.4
3.7
890
42
—
—
3.3
—
—
42
—
—
3.4
—
—
41
42
—
3.2
3.6
—
41
42
—
3.3
3.7
—
41
42
—
3.4
3.8
—
41
40
—
3.5
3.2
—
41
40
—
3.6
3.3
—
41
39
40
3.7
3.2
3.4
41
39
40
3.8
3.3
3.5
905
42
—
—
3.2
—
—
42
—
—
3.3
—
—
42
—
—
3.4
—
—
41
42
—
3.2
3.6
—
41
42
—
3.3
3.7
—
41
42
—
3.4
3.8
—
41
40
—
3.5
3.2
—
41
40
—
3.6
3.3
—
41
39
40
3.7
3.2
3.4
920
43
—
3.8
—
42
—
3.2
—
42
—
3.3
—
42
—
3.4
—
41
42
3.2
3.5
41
42
3.3
3.7
41
42
3.4
3.8
41
40
3.5
3.2
41
40
3.6
3.3
935
43
—
3.7
—
43
—
3.8
—
42
—
3.2
—
42
—
3.3
—
42
—
3.4
—
41
42
3.2
3.5
41
42
3.3
3.7
41
42
3.4
3.8
41
40
3.5
3.2
950
43
—
3.6
—
43
—
3.7
—
43
—
3.8
—
42
—
3.2
—
42
—
3.3
—
42
—
3.4
—
41
42
3.2
3.5
41
42
3.3
3.6
41
42
3.4
3.7
965
43
—
3.4
—
43
—
3.6
—
43
—
3.7
—
43
—
3.8
—
42
—
3.2
—
42
—
3.3
—
42
—
3.4
—
41
42
3.2
3.5
41
42
3.3
3.6
980
44
43
3.8
3.3
42
—
3.5
—
43
—
3.6
—
43
—
3.7
—
43
—
3.8
—
42
—
3.2
—
42
—
3.3
—
42
—
3.4
—
41
42
3.2
3.5
995
44
43
3.7
3.2
44
43
3.8
3.4
43
—
3.5
—
43
—
3.6
—
43
—
3.7
—
43
—
3.8
—
42
—
3.2
—
42
—
3.3
—
42
—
3.4
—
1010
44
—
3.6
—
44
43
3.7
3.3
44
43
3.8
3.4
43
—
3.5
—
43
—
3.6
—
43
—
3.7
—
43
—
3.8
—
42
—
3.2
—
42
—
3.3
—
1025
44
—
3.5
—
44
43
3.6
3.2
44
43
3.7
3.3
43
—
3.4
—
43
—
3.5
—
43
—
3.6
—
43
—
3.7
—
43
—
3.8
—
43
—
3.2
—
1040
44
—
3.4
—
44
—
3.5
—
44
43
3.6
3.2
44
43
3.7
3.3
43
—
3.4
—
43
—
3.5
—
43
—
3.6
—
43
—
3.7
—
43
—
3.8
—
1055
44
—
3.3
—
44
—
3.4
—
44
—
3.5
—
44
43
3.6
3.2
44
43
3.8
3.3
43
—
3.4
—
43
—
3.5
—
43
—
3.6
—
43
—
3.7
—
1070
44
—
3.2
—
44
—
3.3
—
44
—
3.4
—
44
—
3.5
—
44
43
3.7
3.2
44
43
3.8
3.3
43
—
3.4
—
43
—
3.5
—
43
—
3.6
—
1085
45
—
3.8
—
44
—
3.2
—
44
—
3.3
—
44
—
3.4
—
44
—
3.6
—
44
43
3.7
2.3
44
43
3.8
3.3
43
—
3.4
—
43
—
3.5
—
1100
45
—
3.7
—
45
—
3.8
3.4
44
—
3.2
—
44
—
3.4
—
44
—
3.5
—
44
—
3.6
—
44
43
3.7
3.2
44
43
3.8
3.3
43
—
3.4
—
—12—