3. Remove the screws securing the pressure control and
remove it from the unit. Check that the new pressure
control part number is correct for your application (refer
to Table 1). Install the new pressure control.
4. Replace the hose and wiring as originally connected.
ORIFICE SIZE SELECTION
A number of factors determine the correct orifice usage for your
application. These factors include the original orifice sizing,
BTU content of the gas and the altitude.
The standard orifice used in the furnace is shown in Table 2.
Find your unit and determine the standard orifice provided.
For natural gas applications, contact your gas supplier for the
actual BTU content (heating value) of the fuel provided at your
altitude. Table 3 indicates various BTU content fuels.
Use the BTU heating value that is nearest to your value. Read
across the selected table from the standard orifice to the
altitude for your application and the note the new orifice num-
ber.
EXAMPLE: If your unit has a #45 orifice as standard
and a heating gas value of 900 BTU/CU.FT., at an
altitude of 7,000 feet a #47 orifice will provide the correct
firing rate.
For propane (LP) gas applications, Use Table 4 to select the
proper high altitude orifice size.
WARNING: The furnace must first be converted to
use propane (LP) gas through the use of the standard
propane conversion kit accessory.
After selecting the proper orifice size for your application, see
the listing on Table 5 that indicates the part number for your
required orifice number. The orifices may be obtained through
your local Source 1 Parts Distribution Center.
The high altitude orifices should be changed by the following
procedure:
1. Carefully remove the wires from the gas valve and note
their location so they may be properly replaced. Remove
the burner box door. Remove the two screws that hold the
manifold to the burner box and slide the manifold and
orifices back out of the burners.
2. Remove the main burner orifices from the manifold and
discard them
3. Install the derate main burner orifices in the manifold and
tighten them. After installing a new orifice in each location,
any leftover orifices may be discarded.
Input
(MBH)
Output
(MBH)
Natural
Orifice Size
Propane
Orifice Size
Upflow-Downflow/Horizontal Models
60 / 39
55 / 36
# 45
# 55
80 / 52
75 / 48
# 45
# 55
100 / 65
95 / 60
# 45
# 55
120 / 78
112 / 72
# 45
# 55
TABLE 2
- STANDARD ORIFICE USAGE
TABLE 3
- ALTITUDE/NATURAL GAS HEATING VALUE ORIFICE SECTION
TABLE 4
- ALTITUDE/PROPANE (LP) GAS HEATING VALUE ORIFICE SECTION
Natural Gas
Heating Value
(Manifold Pressure
3.5" W.C.)
Orifice
Shipped
With Unit
Recommended Orifice
Altitude (Ft. Above Sea Level)
0
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
10,000
1200
BTU/CU.FT.
45
48
49
49
50
50
50
51
51
52
52
43
45
46
47
47
47
48
48
49
49
49
1100
BTU/CU.FT.
45
47
48
48
49
49
49
50
50
51
51
43
44
45
45
45
46
47
47
48
48
49
1000
BTU/CU.FT.
45
45
46
47
47
47
48
48
49
49
50
43
43
44
44
44
45
45
46
47
47
48
900
BTU/CU.FT.
45
44
45
45
45
46
47
47
48
48
49
43
42
42
43
43
43
44
44
45
46
47
800
BTU/CU.FT.
45
43
44
44
44
45
45
46
47
47
48
43
39
40
41
41
42
42
43
43
44
44
Propane Gas
Heating Value
(Manifold Pressure
10.0" W.C.)
Propane
Orifice @
Sea Level
Recommended Orifice
Altitude (Ft. Above Sea Level)
0
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
10,000
2516
BTU/CU.FT.
54
54
54
55
55
55
55
55
56
56
56
55
55
55
55
55
56
56
56
56
56
57
56
56
56
56
57
57
57
58
59
59
60
650.78-N2.1V
2
Unitary Products Group
