The gas control (Figure 13) has two separate
pressure regulator adjustment screws, one for 1
st
stage
(marked "LO") and the second one for 2
nd
stage (marked
"HI").
The adjusting screws are positioned on either
side of the barbed fitting. The pressure regulator
adjustment is sensitive: one turn of the adjusting
screw will result in a relatively large change in
manifold pressure. Turn regulator-adjusting screws
IN (clockwise) to increase pressure, OUT
(counterclockwise) to decrease presure.
Set the unit on high fire and adjust the 2
nd
stage high
fire pressure regulator to the required setting. Disconnect
the violet wire from the "HI" terminal on the gas control
and the burners will drop down to the 1
st
stage low fire,
then adjust the 1
st
stage pressure regulator setting as
required. Gas input must never exceed the value shown
on the furnace rating label. These units are equipped for
rated input at manifold pressures of 2.3" w.c. (1
st
stage)
and 3.5" w.c. (2
nd
stage) for natural gas. When these
furnaces have been converted for use with LP (propane)
gas, the manifold pressures are 6.4" w.c. (1
st
stage) and
10.0" w.c. (2
nd
stage). After proper adjustments,
reconnect violet wire and furnace should go up to 2
nd
stage high fire. Turn OFF gas, replace manifold pressure
tap pipe plug, regulator adjustment vent cap, and turn ON
gas.
At higher altitudes and varying heating valves,
manifold pressure or orifice changes maybe
required. Consult Tables 7 and 8 for appropriate
values. Failure to follow this warning could lead to
a hazardous furnace operating condition and result
in serious bodily injury or loss of life.
Determining Furnace Input - Natural Gas Only
NOTE:
All access doors must be in place when checking
gas input.
1. Turn OFF all other gas appliances (except for pilot
burners) served by the same gas meter.
2. With furnace operating in full heat cycle, note how
many seconds it takes for one full revolution of the
smallest dial on the meter. Typically, this will be a
1/2 - or - 1 - cubic foot test dial.
3. Using the number of seconds for one revolution and
the size of the meter dial, determine the cubic foot
per hour of gas flow by using the formula provided
below or Table 5.
Cubic Ft/Hr =
Number of Dial Revolutions x Cubic Foot/Revolution x 3600
Time (in seconds) Required for Number of Timed Revolutions
TABLE 5
Gas Rate (Cubic Feet per Hour)
Seconds for
One
Revolution
TEST DIAL
1/2
Cubic
Feet
1
Cubic
Foot
2
Cubic
Feet
10
160
360
720
12
150
300
600
14
129
257
514
16
113
225
450
18
100
200
400
20
90
180
360
22
82
164
325
24
75
150
300
26
69
138
276
28
64
129
258
30
60
120
240
32
56
113
226
34
53
106
212
Seconds for
One
Revolution
TEST DIAL
1/2
Cubic
Feet
1
Cubic
Foot
2
Cubic
Feet
36
50
100
200
38
47
95
190
40
45
90
180
42
43
86
172
44
41
82
164
46
39
78
156
48
37
75
150
50
36
72
144
52
35
69
138
54
34
67
134
56
32
64
128
58
31
62
124
60
30
60
120
4. Calculate the furnace input using the following
formula:
BTUH = Cubic Ft/Hr x BTU/Cubic Foot
The local gas supplier should be able to provide the
heating value of the gas, in BTU/cubic foot. If a
specific value is not available, use 1000 BTU/cubic
foot for Natural gas or 2500 BTU/cubic foot for
Propane (LP).
Furnace input should be maintained within ± 2% of
the value on the rating plate or appropriate altitude
derate. Adjust manifold pressure or change
orifices size if required.
5. Calculate the unit's actual input rate.
Example:
If the heating value of the natural gas is 1015
Btu/cu. and it takes 60 seconds to burn 2 cu.
ft. of gas then:
Input = 1015 Btu/cu. ft. X 1 rev X 2 cu. ft./rev. X 3600
60 sec.
Input = 121,800 Btu/hr.
20571201
Issue 0527
Page 20 of 28
