Specifications

035-17377-000 REV A (0201)
Unitary Products Group 45
1. To determine the rate of gas flow (second Stage).
2. Turn of all other gas appliances connected to the gas
meter.
3. Turn on the furnace and make sure the thermostat is
calling for Second stage (100% input) heat.
4. Measure the time needed for one revolution of the hand
on the smallest dial on the meter. A typical gas meter
has a 1/2 or a 1 cubic foot test dial.
5. Using the number of seconds it takes for one revolution
of the dial, calculate the cubic feet of gas consumed per
hour. (See example below).
6. If necessary, adjust the high pressure regulator as dis-
cussed in the section “Manifold Gas Pressure Adjust-
ment”. Be sure not to over-fire the furnace on Second
stage. If in doubt, it is better to leave the Second stage
of the furnace slightly under-fired. Repeat Steps 1-5.
To determine the rate of gas flow (First Stage)
1. Turn of all other gas appliances connected to the gas
meter.
2. Turn on the furnace and make sure the thermostat is
calling for first stage (60% input) heat.
3. Even when the thermostat is calling for first stage heat,
the unit will light on second stage and will run on Second
stage for 1 minute. Allow this one-minute time period to
expire and be certain the unit is running on first stage.
4. Measure the time needed for one revolution of the hand
on the smallest dial on the meter. A typical gas meter
has a 1/2 or a 1 cubic foot test dial.
5. Using the number of seconds it takes for one revolution
of the dial, calculate the cubic feet of gas consumed per
hour (See example below).
6. If necessary, adjust the low pressure regulator as dis-
cussed in the section “Manifold Gas Pressure Adjust-
ment”. Be sure not to under-fire the furnace on first
stage. If in doubt, it is better to leave the first stage of the
furnace slightly over-fired (greater than 60% input).
Repeat Steps 1-6.
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 as it varies widely from area to area).
EXAMPLE
By actual measurement, it takes 19 seconds for the hand on
a 1 cubic foot dial to make a revolution with a 192,000 Btuh
furnace running. To determine rotations per minute, divide 60
by 19 = 3.16. To calculate rotations per hour, multiply 3.16 •
60 = 189.6. Multiply 189.6 • 1 (0.5 if using a 1/2 cubic foot
dial) = 189.6. Multiply 189.6 • (the Btu rating of the gas). For
this example, assume the gas has a Btu rating of 1050
Btu/ft.
3
. The result of 199,000 Btuh is within 5% of the
192,000 Btuh rating of the furnace.
TABLE 50: GAS HEAT STAGES
# of Burner Tubes
2nd Stage
Input (100%
Btuh)
1st Stage
Input (60%)
Btuh
4
120,000 72,000
6
180,000 108,000
8
240,000 144,000
TABLE 51: GAS RATE CUBIC FEET PER HOUR
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