6.For Honeywell gas valves with the regulator converter (Figure 28, page 19):
a.Unscrew the pressure regulator cap and check for the letters NAT or LP.
b.Invert the cap and tighten until snug.
7.For Robertshaw gas valves with the regulator converter (Figure 29):
a.Remove the black cover and unscrew the converter located on top of the gas valve.
b.Invert the converter: for LP the red ring will be located at the bottom and the LP stamping on the converter will appear right side up.
c.Screw converter back into the regulator, hand tight plus 1/8 turn. Replace the black cover on the converter top to protect the threads.
8.Reassemble the burner assembly into the furnace.
9.Reconnect the gas piping and electrical wires to the gas valve.
10.Open the manual
High Altitude Conversion
High altitude conversion with this furnace depends on the installation altitude and the heating value of the gas. The installation of this furnace at altitudes above 2,000 feet must meet the requirements of the National Fuel Gas Code or local jurisdiction.In Canada, the requirements for high altitude are different and governed by CGA B149.1. Please consult your local code authority.
WARNING:
The reduction of input rating nec- essary for high altitude installation may only be accomplished with factory supplied orifices. Do not attempt to drill out orifices in the field. Improperly drilled orifices may cause fire, explosion, carbon monoxide poisoning, personal injury or death.
This furnace is shipped from the factory with orifi ces and gas regulator settings for natural gas operation at sea level altitudes. At 2000 feet, the NFGC requires that this appliance be derated 4% for each 1000 feet of altitude. For example, the input needs to be reduced 8% at 2,000 feet, 12% at 3,000 feet and etc. This deration is in reference to the input rate and gas heating value at sea level. See Table 12 (page 32).
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M11678
Figure 28. Honeywell Gas Valve
LP Gas
Configuration
Red
Black Cover 
Natural Gas
Configuration
Figure 29. Robertshaw Gas Valve
Flue Gas Sampling
It may be necessary to take fl ue gas sampling from oil and gas furnaces (M5S and M1B Series Models) in order to check the performance after furnace installation. A fl ue gas sample may be taken from the heat exchanger, which is located behind the hole of the
1.Turn off all electric power to the appliance.
2.Remove the black plastic cap located above the blower. Do not discard cap.
3.Drill a hole through the top of the blower compartment. NOTE: Hole diameter should be same size as sampling tube.
4.Insert sampling tube through the drilled hole and into the heat exchanger.
5.After a complete check and adjustment of furnace performance, seal the drilled hole with a screw larger than the hole. NOTE: Seal the screw threads with silicon sealant - rated at least 500° F.
6.Plug the outside hole with the plastic cap removed in step 3.
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