High altitude air pressure switch, Changing orifices for high altitude, A 1#vari\iii\ig – Sears 9MPD User Manual
Page 31: General derating rules
Attention! The text in this document has been recognized automatically. To view the original document, you can use the "Original mode".
MANIFOLD PRESSURE AND ORIFICE SIZE FOR HIGH ALTITUDE APPLICATIONS
Tnljle 7
NATURAL GAS
Heat Value
Btu/Cu.Ft.
Elevation Above Sea Level
0-1999
(" -wc)
2000-2999
(" wc)
3000-3999
(" -wc)
4000-4999
(" -wc)
5000-5999
(" -wc)
6000-6999
(" -wc)
7000-7999
("
‘Wc)
800
3.5
3,5
3.5
3,5
3.5
3.5
3.5
850
3.5
3.5
3.5
3.5
3.5
3.5
3.5
900
3.5
3.5
3.5
3.5
3.5
3.5
3.4
950
3.5
3.5
3.5
3.5
3.3
3.2
3.1
1000
3.5
3.4
3.3
3.2
3.0
2.9
2.8
1050
3.2
3,1
3.0
2,9
2.7
2.6
2,5
1100
2.9
2,8
2.7
2,6
2.5
2.4
2.3
Orifice Size
и
и
* #42 Orifice size for 50,000, 75,000 100,00 & 125,000 BTUH models
#44 Orifice size for 80,000 BTUH model
General Derating Rules
For operation with natural gas at altitudes above 2,000',
orifice change and/or manifold pressure adjustment may
be required to suit gas supplied. Check with gas supplier. If
orifice sizing is needed, it should be based on reducing the
input rating by 2% (natural) or 4% (LP) for each 1,000'
above sea level. See
Table 7
and
Figure 28
for required
pressure change and/or orifice change for high altitudes.
For operation with LP gas at altitudes above 2,000 , gas ori
fices
MUST
be changed and manifold pressure
MUST
be
maintained
as per
Table
6
. For the 50,000, 75,000,
100.000 and 125,000 BTUFI Orifice sizes are #54 for
0-2000' above sea level, #55 for 2000' -7000' above sea
level, and #56 for 7000' -8000' above sea level. For the
80.000 BTUH models, the orifice size is #55 for 0 - 4,000'
above seal level and #56 for 5,000' - 8,000' above sea lev
el. Orifices can be ordered through your distributor.
(See
Figure 28)
NOTE: The derating of these units at 2% (Natural) and 4% (L.P.)
has been tested and approved by AGA.
High Altitude Air Pressure Switch
Altitudes over 4,000' require a different air pressure switch than
the one installed at the factory. Check parts list for pressure switch
and consult your distributor for part number and availability. In
Canada, provincial codes may govern installation of switch.
Check with governing authorities.
Changing Orifices for High Altitude
A 1#VARI\III\IG
ELECTRICAL SHOCK, FIRE OR EXPLOSION HAZARD
Failure to properly install orifices can result in death,
personal injury and/or property damage.
Turn OFF electric power (at disconnect) and gas supply
(at manual valve in gas line) when installing orifices.
Installation
of
orifices
requires
a
qualified
service
technician.
NOTE:
Main burner orifices can be changed for high altitudes.
1. Disconnect gas line from gas valve.
Remove manifold from furnace.
2
.
3.
4.
5.
Remove the orifices from the manifold and replace them
with properly sized orifices.
Tighten orifices so it is seated and gas tight.
(See
Figure 28)
Reinstall manifold. Ensure burners do
NOT
bind on new
orifices.
44001
1114
00
[jj]