1183746-UIM-B-0215
18 Johnson Controls Unitary Products
Direct Drive Blower
All units have direct drive, multi speed standard ECM blower motors.
CHECKING GAS HEAT 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 revo-
lution 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 15.
If the actual input is not within 5% of the furnace rating with allowance
being made for the permissible range of the regulator setting, replace
the orifice spuds with spuds of the proper size.
NOTICE
To find the BTU input, multiply the number of cubic feet of gas con-
sumed 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 15: Gas Rate Cubic Feet Per Hour
1
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 38 seconds in the first column of
Table 15. Read across to the column headed “1 Cubic Foot,” where you will
see that 95 cubic feet of gas per hour are consumed by the furnace at that
rate. Multiply 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.
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
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