280241-YIM-D-0909
22
Johnson Controls Unitary Products
CHECKING GAS INPUT
NATURAL GAS
1.
Turn off all other gas appliances connected to the gas
meter.
2.
With the furnace turned on, measure the time needed for
one revolution of the hand on the smallest dial on the
meter. A typical gas meter usually has a 1/2 or a 1 cubic
foot test dial.
3.
Using the number of seconds for each revolution and the
size of the test dial increment, find the cubic feet of gas
consumed per hour from Table 14.
If the actual input is not within 5% of the furnace rating with
allowance being made for the permissible range of the regu-
lator setting, replace the orifice spuds with spuds of the
proper size.
NOTE:
To find the BTU input, multiply the number of cubic
feet of gas consumed per hour by the BTU content
of the gas in your particular locality. (Contact your
gas company for this information since it varies
widely from city to city.)
TABLE 14: GAS RATE - CUBIC FEET PER HOUR
1
SECONDS
FOR ONE
REV.
SIZE OF TEST DIAL
1/2 CU. FT.
1 CU. FT.
10
180
360
12
150
300
14
129
257
16
113
225
18
100
200
20
90
180
22
82
164
24
75
150
26
69
138
28
64
129
30
60
120
32
56
113
34
53
106
36
50
100
38
47
95
40
45
90
42
43
86
44
41
82
46
39
78
48
37
75
50
36
72
52
35
69
54
34
67
56
32
64
58
31
62
60
30
60
1.
EXAMPLE
: By actual measurement, it takes 38 seconds for the hand on the 1-cubic foot dial to make a revolution with just a
100,000 BTUH furnace running. Using this information, locate 28 seconds in the first column of Table 14. Read across to the col-
umn headed “1 Cubic Foot,” where you will see that 95 cubic feet of gas per hour are consumed by the furnace at that rate. Multi-
ply 95 x 1050 (the BTU rating of the gas obtained from the local gas company). The result is 99,750 BTUH, which is close to the
100,000 BTUH rating of the furnace.
