035-14370-000
650.75-N4U
Unitary Products Group
29
EXAMPLE - CHECKING GAS INPUT
It is found by measurement that it takes 26 seconds for the
hand on the 1 cubic foot dial to make a revolution with only a
120,000 Btuh furnace running. Using this information, locate
26 seconds in the first column of Table 9, “gas rate (cubic feet
per hour),” on page 29. Read across to the column headed 1
cubic foot where you will see that 138 cubic feet of gas per
hour are consumed by the furnace at that rate.
With the barometer at 28.9" and a 70° F temperature, the cor-
rection factor will be.945. If the local gas heating value is 935
BTU per cubic foot the calculations will be as follows:
138 cu. ft/hrx.945 correction factor x 935 BTU/cu. ft. =
121,933 BTU/Hr.
The calculated firing rate of 121,933 BTU per hour is within
the
+2% tolerance of our nominal 120,000 furnace..
If the actual input is not within
+2% of the furnace rating, with
allowance being made for the permissible range of the regu-
lator setting (0.3 inches W.C.), replace the orifice spuds with
spud of the proper size.
ADJUSTMENT OF MANIFOLD GAS PRESSURE
Manifold gas pressure may be measured by two different pro-
cedures. It may be measured with the burner box cover in
place or it may be measured with the burner box cover
removed. Follow the appropriate section, 2a or 2b in the
instructions below.
1.
Turn gas off at main gas valve. Revove 1/8” Allen socket
head pipe plug from the manifold end of the main gas
valve. Install the proper manometer tube adapter into
this opening.
2.
Read the inlet gas pressure using either of the two meth-
ods below.
a.
Reading the gas pressure with the burner box
cover in place - Disconnect the pressure reference
hose from the right side of the burner box. Using a
tee fitting and a short piece of hose, connect the
negative side of the manometer to the burner box
pressure reference port. Connect the positive side
of the manometer to the adapter previously installed
in the gas valve Refer to Figures 39 and 40 on
page 31.
b.
Reading the gas pressure with the burner box
cover removed - Remove the screws securing the
burner box front cover plate. Remove the cover. It is
gasketed and may stick in place. Connect the posi-
tive side of the manometer to the adapter previously
installed in the gas valve as shown in Refer to Fig-
ures 39 and 40 on page 31. There will be no second
connection to the manometer as it will reference
atmospheric pressure.
NOTE:The screw-off cap for the pressure regulator must be
removed entirely to gain access to the adjustment screw.
Loosening or tightening the cap does not adjust the flow of
gas.
Be sure to relight any gas appliance that were
turned off at the start of this input check.
TABLE 9 : GAS RATE (CUBIC FEET PER HOUR)
SECONDS
FOR
ONE
REVOLUTION
SIZE
OF
TEST
DIAL
1/2
CUBIC
FOOT
1
CUBIC
FOOT
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
