25
80+ HIGH ALTITUDE
INSTRUCTIONS (TABLE 8)
THE NATIONAL FUEL GAS CODE
(NFGC) GUIDELINES SHOULD BE
FOLLOWED WHEN CONVERTING
THESE FURNACES FOR HIGH
ALTITUDE OPERATION.
34" 80 Plus furnaces installed above
2,000 ft. require the furnace to be de-
rated 4% per thousand feet.
IMPORTANT: Factory installed orifices
are calculated and sized based on a sea
level Natural Gas heating value of 1075
BTU per cubic ft.
NOTE: Orifices are available through
your local distributor.
Reference Table 8 for appropriate orifice
sizing.
NOTE: Keep any parts removed during
LP conversion procedure stored with the
product literature for future use.
The following are examples of orifice
sizing using the National Fuel Gas Code
Appendix F:
Example: 900 BTU/ft
3
Regional
Natural Gas Heating Value
I/H = Q
25000 / 900 = 27.78 ft
3
I = Sea Level input (per burner): 25000
H = Sea Level Heating Value: 900
Q = 27.78 ft
3
Natural Gas per hour.
From Table F.1 of National Fuel Gas
Code Handbook, 2002 (3.5 w.c.
column).
Orifice required at Seal Level: #40
From Table F.4 of National Fuel Gas
Code Handbook, 2002
Orifice required at 5000 ft. elevation (4%
de-rate per thousand ft): #42
Orifice required at 8000 ft. elevation (4%
de-rate per thousand ft.): #44
Example: 1050 BTU/ft3 Regional
Natural Gas Heating Value
I / H = Q
25000 / 1050 = 23.81ft
3
I = Sea Level input (per burner): 25000
H = Sea Level Heating Value: 1050
Q = 23.81 ft
3
Natural Gas per hour.
From Table F.1 of Natural Fuel Gas
Code Handbook, 2002 (3.5 w.c.
column).
Orifice required at Sea Level: #43
From Table F.4 of National Fuel Gas
Code Handbook, 2002
Orifice required at 5000 ft. elevation (4%
de-rate per thousand ft.): #45
Orifice required at 8000 ft elevation (4%
de-rate per thousand ft): #47
LP GAS (TABLE 6)
LP Gas is a manufactured gas that has
consistent heating value across most
regions.
The NFGC guidelines are used with the
following exception:
The recommended LP Gas high
altitude orifice selections differ slightly
in that the NFGC LP orifice chart, as
they are not accurate for Rheem
products. The National Fuel Gas Code
LP orifices are based on an 11" of
water column pressure at the orifice,
which differs from products that use 10"
of water column at the orifice. This
difference requires a deviation from the
NFGC orifice size recommendations.
The Sea Level input should still be
reduced by 4% per thousand ft. and the
orifice size must be selected based on
the reduced input in Table 6.
ORIFICE ORDERING
INFORMATION
Orifice sizes are selected by adding the
2-digit drill size required in the orifice
part number. Drill sizes available are 39
through 64; metric sizes available
1.10mm (-90) and 1.15mm (-91):
Orifice Part Number 62-22175-(drill
size)
Example 1:
# 60 drill size orifice required
Part # 62-22175-60
Example 2:
1.15mm drill size orifice required
Part # 62-22175-91
ALTERNATE METHOD FOR
CANADIAN
HIGH-ALTITUDE
DERATE
In Canada, unless an orifice change is
specifically mandated by local codes,
an alternate method of altitude deration
through a reduction in manifold
pressure is acceptable as described in
Table 7. This information is based on a
heating value of 1000 BTU per cubic
feet of natural gas, and 2500 BTU per
cubic feet of LP gas.
IMPORTANT: Actual input rates must
be measured onsite with manifold
pressure adjustment to ensure that an
actual 10% reduction in input rate is
achieved.
Once this field adjustment has been
made, the label shown in Figure 20
must be affixed in a conspicuous
location on the front of the furnace
cabinet.
NOTE: This label is supplied in the
information packet shipped with each
furnace.
TABLE 7
ALTERNATE METHOD FOR CANADIAN
HIGH-ALTITUDE DERATE
NATURAL GAS LP GAS
FIGURE 20
MANIFOLD PRESSURE-CHANGE LABEL
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