54
Marvair GAA A/C w/Gas Heat I&O Manual
06/2023 Rev.5
HMG 22,500 BTUH / Burner
( Used with GAA1024-1036 Heat Exchangers )
HMG 25,000 BTUH / Burner
( Used with GAA1042-1060 Heat Exchangers )
Altitude
Orifice- Natural
Orifice- Propane
Altitude
Orifice- Natural
Orifice- Propane
Drill Size
Dia.
Drill Size
Dia.
Drill Size
Dia.
Drill Size
Dia.
0-1999 ft
#43
0.089
#54
0.055
0-1999 ft
2.30
0.0906
1.5
0.0591
2000-2999 ft
2.2
0.0866
1.35
0.531
2000-2999 ft
#43
0.0890
#54
0.0550
3000-3999 ft
2.15
0.0846
#55
0.052
3000-3999 ft
2.20
0.0866
1.35
0.0531
4000-4999 ft
2.1
0.0827
1.3
0.0511
4000-4999 ft
2.15
0.0846
#55
0.0520
5000-5999 ft
#45
0.082
1.25
0.0492
5000-5999 ft
2.10
0.0827
1.30
0.0511
6000-6999 ft
2.05
0.087
1.2
0.0472
6000-6999 ft
#45
0.0820
1.25
0.0492
Burner
Input
Number of
Orifices
Burner
Input
Number of
Orifices
40,500
2
81,000
4
45,000
2
90,000
4
60,750
3
100,000
4
67,500
3
112,500
5
75,000
3
125,000
5
Orifice Size
( mm )
Orifice
Diameter
Orifice Size
( mm )
Orifice
Diameter
2.10
0.0826
2.45
0.0964
2.15
0.0846
2.50
0.0984
2.20
0.0866
2.60
0.1024
2.25
0.0885
2.70
0.1063
2.30
0.0905
2.75
0.1082
2.35
0.0925
2.80
0.1102
2.40
0.0945
2.90
0.1142
Table 7. Altitude / Orifice Sizing
NOTE:
Data for LP gas is based upon a 0.60 specific gravity. For fuels with different specific gravity,
consult the National Fuel Gas Code ANSI Z223.1/NFPA 54-2002 or the National Standard of Canada,
Natural & Propane Gas Installation Code CSA B149.1-00.
High Altitude Air Pressure Switch
The factory installed pressure switch is factory set for installations from sea level up to 6,000 ft
( 1,829 m ). Consult the factory for installations above 6,000 ft.
5.7 Changing Orifices
1. Turn OFF gas at the shut off valve.
2. Turn off all power to the unit at the fuse box or service panel.
3. Remove the burner compartment door, exposing the burner.
4. Disconnect the gas line from gas valve so that manifold can be removed.
5. Disconnect wiring at the gas valve. Be sure to note or mark the location of all electrical connections.
6. Remove the 4 screws holding the manifold and gas valve to the manifold supports. Keep screws.
7. Carefully remove the manifold assembly.
8. Remove the orifices from the manifold and replace them with the proper sized orifices.
9. Tighten orifices so that they are seated and gas tight.
10. Reassemble all parts in the reverse order as removed. Be sure to engage the main burner orifices in
the proper openings in the burners.
