66399-YIM-C-0405
70
Unitary Products Group
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
- it varies widely from city to city.)
ADJUSTMENT OF TEMPERATURE RISE
The temperature rise (or temperature difference
between the return air and the heated air from the fur-
nace) must lie within the range shown on the rating
plate and the data in the Gas Heat Application Table 4.
After the temperature rise has been determined, the
cfm can be calculated as follows:
After about 20 minutes of operation, determine the fur-
nace temperature rise. Take readings of both the return
air and the heated air in the ducts (about six feet from
the furnace) where they will not be affected by radiant
heat. Increase the blower cfm to decrease the temper-
ature rise; decrease the blower cfm to increase the
rise. Refer to the Blower Motor and Drive Data
Table 48.
TROUBLESHOOTING
COOLING TROUBLESHOOTING GUIDE
TABLE 54: GAS RATE - CUBIC FEET PER HOUR
1
1.
By actual measurement, it takes 38 seconds for the hand on
the 1-cubic foot dial to make a revolution with a 100,000
Btuh furnace running. Using this information, located 38
seconds in the first column in the table above. 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 fur-
nace 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
Troubleshooting of components may require
opening the electrical control box with the
power connected to the unit.
Use extreme
care when working with live circuits!
Check
the unit nameplate for the correct line voltage
and set the voltmeter to the correct range
before making any connections with line termi-
nals.
Shut off all electric power to the unit prior to
any of the following maintenance procedures
to prevent personal injury.
CFM
Btuh Input x 0.8
=
108
.
.
x F Temp Rise
o
