32
18-CD33D1-4
Installer’s Guide
GAS FLOW IN CUBIC FEET PER HOUR
2 CUBIC FOOT DIAL
SEC. FLOW SEC. FLOW SEC. FLOW SEC. FLOW
8
900
29
248
50
144
82
88
9
800
30
240
51
141
84
86
10
720
31
232
52
138
86
84
11
655
32
225
53
136
88
82
12
600
33
218
54
133
90
80
13
555
34
212
55
131
92
78
14
514
35
206
56
129
94
76
15
480
36
200
57
126
96
75
16
450
37
195
58
124
98
73
17
424
38
189
59
122
100
72
18
400
39
185
60
120
104
69
19
379
40
180
62
116
108
67
20
360
41
176
64
112
112
64
21
343
42
172
66
109
116
62
22
327
43
167
68
106
120
60
23
313
44
164
70
103
124
58
24
300
45
160
72
100
128
56
25
288
46
157
74
97
132
54
26
277
47
153
76
95
136
53
27
267
48
150
78
92
140
51
28
257
49
147
80
90
144
50
TABLE 13
Q
Input rate changes can be made by adjusting the mani-
fold pressure (min 3.0 - max 3.7 in. W.C. - Natural Gas) or
changing orifices (orifice change may not always be re-
quired). If the desired input rate can not be achieved with
a change in manifold pressure, then the orifices must be
changed. LP installations will require an orifice change.
Installation of this furnace at altitudes above 2,000 ft.
(610m) shall be in accordance with local codes, or in the
absence of local codes, the
National Fuel Gas Code,
▲
CAUTION
!
Replace and/ or tighten all plugs removed or loosened
when adjusting gas pressure. Leak check the fittings
before placing the furnace into regular service.
Failure to follow this warning could result in fire, explo-
sion, or property damage.
NOTE:
The manifold pressure must be referenced to the burn-
er box. The burner box pressure tap equalizes the gas
valve pressure regulator. Manifold pressure is checked
by installing a tee (field supplied) in the tubing, be-
tween the tee coming from the burner box tube and the
gas valve, in addition to the regular gas valve pressure
tap on the outlet side of the gas valve. See Figure 51.
▲
CAUTION
!
Replace manifold pressure tap threaded plug and leak
check after checking/ adjusting manifold gas pressure.
Table 11 lists the main burner orifices used with the fur-
nace. If a change of orifices is required to correct the fur-
nace input rating refer to Table 14.
TABLE 12
FINAL MANIFOLD PRESSURE SETTINGS
FUEL
PRESSURE
NATURAL GAS
3.5" W.C.
LP GAS
11.0" W.C.
HIGH ALTITUDE DERATE
Input ratings (BTUH) of these furnaces are based on sea
level operation and should not be changed at elevations
up to 2,000 ft.
If the installation is 2,000 ft. or above, the furnace input
rate (BTUH) shall be reduced 4% for each 1,000 ft. above
sea level. The furnace input rate shall be checked by
clocking the gas flow rate (CFH) and multiplying by the
heating value obtained from the local utility supplier for
the gas being delivered at the installed altitude.
