24
88-A952V001-1B-EN
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. (610
m).
If the installation is 2,000 ft. (610 m) or above, the Furnace input rate
(BTUH) shall be reduced 4% for each 1,000 ft. above sea level.
Installations of this furnace at altitudes above 2,000 ft. (610 m) shall
be made utilizing the Vent Length table and/or Part Numbers for
Replacement Orifices table in these installation instructions.
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.
Input rate changes can be made by adjusting the Manifold Pressure
(min 3.0 - max 3.7 in. W.C. - Natural Gas) or changing orifices (orifice
change may not always be required).
If the desired input rate can not be achieved with a change in Manifold
Pressure, then the orifices must be changed. Propane installations will
require an orifice change.
Important:
Reinstall the replacement orifices to the same depth as
the orifices supplied with the equipment.
See the table for help in selecting orifices if orifice change is required.
Furnace input rate and temperature rise should be checked again after
changing orifices to confirm the proper rate for the altitude.
The vent length table shows the required vent lengths for installations
at various altitudes. Installations above 12,000 feet are not allowed.
PART NUMBERS FOR REPLACEMENT ORIFICES
DRILL SIZE
PART
NUMBER
DRILL SIZE
PART
NUMBER
44
ORF00501
54
ORF00555
45
ORF00644
55
ORF00693
46
ORF00909
56
ORF00907
47
ORF00910
57
ORF00908
48
ORF01099
58
ORF01338
49
ORF00503
59
ORF01339
50
ORF00493
Turn the main Gas Valve toggle switch within the unit to the "
OFF
"
position. Turn the external gas valve to "ON". Purge the air from the
gas lines. After purging, check all gas connections for leaks with a
soapy solution –
DO NOT CHECK WITH AN OPEN FLAME.
Allow 5
minutes for any gas that might have escaped to dissipate.
Propane Gas being heavier than air may require forced ventilation.
Turn the toggle switch on the Gas Valve in the unit to the "ON"
position.
The table lists the main burner orifices
used with the furnace. If a change of
orifices is required to correct the furnace
input rating refer to the part number for
replacement orifices table.
Installation of this furnace at altitudes
above 2000 ft (610m) shall be in
accordance with local codes, or in the
absence of local codes, the
National Fuel
Gas Code, ANSI Z223.1/NFPA 54
or
National Standard of Canada, Natural
Gas and Propane Installation Code, CSA
B149.1.
Orifice
Twist Drill
Size If
Installed at
Sea Level
Altitude Above Sea Level
and Orifice Required at Other Elevations
2000
3000
4000
5000
6000
7000
8000
9000
10000
42
42
43
43
43
44
44
45
46
47
43
44
44
44
45
45
46
47
47
48
44
45
45
45
46
47
47
48
48
50
45
46
47
47
47
48
48
49
49
50
46
47
47
47
48
48
49
49
50
51
47
48
48
49
49
49
50
50
51
52
54
54
55
55
55
55
55
56
56
56
55
55
55
55
56
56
56
56
56
57
56
56
56
57
57
57
58
59
59
60
57
58
59
59
60
60
61
62
63
63
58
59
60
60
61
62
62
63
63
64
From National Fuel Gas Code — Table E.1.1(d)
