27
440 01 2020 01
Manifold Gas Pressure Adjustment
(Hi & Lo Fire)
NOTE:
Make adjustment to manifold pressure with burners operat-
ing.
ELECTRICAL SHOCK HAZARD.
Failure to do so can result in death, personal injury
and/or property damage.
Turn OFF power to furnace before changing speed
taps.
!
1. Remove the burner compartment door.
2. Reture fourth (4th) DIP switch to previous setting.
3. Replace the burner compartment door.
General Derating Rules
1. For operation with natural gas at altitudes above 2,000
¢
, ori-
fice change and/or manifold pressure adjustment may be re-
quired 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 6
and
Figure 28
for required pressure
change and/or orifice change for high altitudes.
2. 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 5.
Orifice sizes for 0--2000
¢
above
sea level are #54. 2000--7000
¢
above sea level, use #55.
7000--8000
¢
above sea level, use #56 orifices. Orifices can
be ordered through your distributor.
(See Figure 28)
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 gov-
erning authorities.
NOTE:
The derating of these units at 2% (Natural) and 4% (L.P.)
has been tested and approved by CSA.
MANIFOLD PRESSURE AND ORIFICE SIZE FOR HIGH ALTITUDE APPLICATIONS
Table 6
High Altitude Pressure Chart
2000--8000 ft. (Natural Gas)
Heat Value
Elevation Above Sea Level
Heat Value
Btu/Cu.Ft.
0--1999
2000--2999
3000--3999
4000--4999
5000--5999
6000--6999
7000--7999
Btu/Cu.Ft.
High
Low
High
Low
High
Low
High
Low
High
Low
High
Low
High
Low
800
3.5
1.7
3.5
1.7
3.5
1.7
3.5
1.7
3.5
1.7
3.5
1.7
3.5
1.7
850
3.5
1.7
3.5
1.7
3.5
1.7
3.5
1.7
3.5
1.7
3.5
1.7
3.5
1.7
900
3.5
1.7
3.5
1.7
3.5
1.7
3.5
1.7
3.5
1.7
3.5
1.7
3.4
1.7
950
3.5
1.7
3.5
1.7
3.5
1.7
3.5
1.7
3.3
1.6
3.2
1.6
3.1
1.5
1000
3.5
1.7
3.4
1.7
3.3
1.6
3.2
1.5
3.0
1.5
2.9
1.4
2.8
1.4
1050
3.2
1.6
3.1
1.5
3.0
1.5
2.9
1.4
2.7
1.3
2.6
1.3
2.5
1.2
1100
2.9
1.4
2.8
1.4
2.7
1.3
2.6
1.3
2.5
1.2
2.4
1.2
2.3
1.1
Orifice Size
#42
#42
#42
#42
#42
#42
#42
Changing Orifices for High Altitude
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.
2. Remove manifold from furnace.
3. Remove the orifices from the manifold and replace them
with properly sized orifices.
4. Tighten orifices so it is seated and gas tight.
(See Figure 28
)
Figure 28
Changing Orifices
1
1
/
8
²
to 1
3
/
16
²
Measure from face of ori-
fice to the back side of the
manifold.
5. Reinstall manifold. Ensure burners do
NOT
bind on new ori-
fices.
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