Gas and Oil Home Heating Furnaces - Converting furnace burner from LP to NG

I currently use LP on my furnace, but I will be converting to NG shortly. My furnace manual says I need to replace four (4) orifices on my burner with #42 size orifices. I have a Enviro Plus 90 RPJ II Comfortmaker (1994), Model #GUK100AGIN.

I haven't had any luck finding this part on-line any where. I did however locate some #42 orifices for restuarant use (Stove). Are these the same orifices for furnaces? Any help on this would be appreciated.

Thanks!!
RFW

Orifices are usually manufacturer-dependent. That means that there is more to the process than just the correct size hole. You may be able to purchase a generic orifice that will fit your furnace but the proper way is with orifices from the manufacturer.

Understand that there is much more to changing fuels than just the orifice change. You also need to change the gas pressure regulator setting and that may require a new spring or even a new gas valve. There are also combustion tests that need to be made and perhaps adjustments or replacement of other parts. You could even find that the pipeline serving your furnace is not large enough for natural gas. I strongly suggest that you get a factory-authorized technician to do the changeover.

Changing fuels is rarely a DIY job.

Furd is right on the money with his comments about this not being a DIY job. It most certainly needs to be done by a trained, experienced technician. The furnace heat exchanger needs to be inspected/tested to insure safe operation. As I recall, that series of furnaces has a history of heat exchanger problems.

Lets just add that if your combustion is not rigth the first thing that happens is the CO goes up.
I have seen mis-adjusted premix burners that have pegged (and damaged) my combustion analyzer. These readings where 2000 to 4000. If that leaked into your house, you would not stand much chance.

As suggested earlier, it's not just the size but the aerodynamic shape of the whole orifice that determines how much gas gets to the burner.

And it's also correct that the burner manifold pressure is much different. You may need a new gas valve designed for natural gas since there is a regulator built into the gas valve.

And this is not a DIY job. You need a person experienced at this kind of job who can set the input correctly and has test instruments to check the carbon monoxide levels.

Input that's too high or low is a problem, a can be a serious problem.