MANIFOLD PRESSUREAND ORIFICESIZE FOR HIGHALTITUDE APPLICATIONS
NATURAL GAS
MEAN ELEVATION FEET ABOVE SEA LEVEL
HEATING VALUE 0 to 2000 to 3000 to 4000 to 5000 to 6000 to 7000 to
BTU/CU. FT. 1999 2999 3999 4999 5999 6999 8000
800 3.5" wc 3.5" wc 3.5" wc 3.5" wc 3.5" wc 3.5" wc 3.5" wc
850 3.5" wc 3.5" wc 3.5" wc 3.5" wc 3.5" wc 3.5" wc 3.5" wc
900 3.5" wc 3.5" wc 3.5" wc 3.5" wc 3.5" wc 3.5" wc 3.4" wc
950 3.5" wc 3.5" wc 3.5" wc 3.5" wc 3.3" wc 3.2" wc 3.1" wc
1000 3.5" wc 3.4" wc 3.3" wc 3.2" wc 3.0" wc 2.9" wc 2.8" wc
1050 3.2" wc 3.1" wc 3.0" wc 2.9" wc 2.7" wc 2.6" wc 2.5" wc
1100 2.9" wc 2.8" wc 2.7" wc 2.6" wc 2.5" wc 2.4" wc 2.3" wc
Orifice Size #42 #42 #42 #42 #42 #42 #42
PROPANE
MEAN ELEVATION FEET ABOVE SEA LEVEL
HEATING VALUE 0 to 2000 to 3000 to 4000 to 5000 to 6000 to 7000 to
BTU/CU. FT. 1999 2999 3999 4999 5999 6999 8000
2500 10.0" wc 10.0" wc 9.4" wc 10.0" wc 9.8" wc 8.8" wc 7.9" wc
Orifice Size #54 #54 #54 #55 #55 #55 #55
NOTE: NATURAL GAS DATA BASED ON 0.60 SPECIFIC GRAVITY. PROPANE DATA BASED ON 1.53 SPECIFIC GRAVITY. FOR
FUELS WITH DIFFERENT SPECIFIC GRAVITY CONSULT THE LATEST EDITION OF THE NATIONAL FUEL GAS CODE ANSI
Z223.1 and CAN B149.
ChangingOrifices
1. After disconnecting power and gas supply to the furnace, re-
move the access door, exposing the burner compartment.
Manifold (U pflow/Horizontal)
jJ_
25-20-95
2.
3.
4.
Disconnect gas line and pilot tubing from gas valve so man-
ifold can be removed.
Disconnect wiring at gas valve. Be sure to note the proper
location of any and all electrical wiring disconnected.
Remove the four (4) screws holding the manifold and gas
valve to the manifold supports. Do not discard any screws.
See Figure 9 or Figure 10,
5. Carefully remove the manifold assembly.
Manifold (Downflow)
/
//
25-23-15
6. Remove the orifices from the manifold and replace them with
proper sized orifices. See Figure 11.
7. Tighten orifices so it is seated and gas tight. See Figure 11.
Clearances
Measure from face of orifice
( _ j to the back side of the
_anifold.
1.21"
44101260302 [_
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