A friend gave me a Napoleon B36DFN gas fire, and had it converted to propane and there is a tag on the fire that states the conversion happened using #54 connection. I now wish to convert it back to natural gas, and for the life of me I can't get an answer from the manufacturer Napoleon. I guess its a liability thing! I live in Canada.
I googled 'Napoleon B36DFN LP conversion' and the very first hit is for page 17 of the user manual for that fireplace. See here: http://bit.ly/1HHpEP5
It states in relevant part: "To convert from Propane to Natural Gas order conversion kit # W175-023"
Googling for 'W175-023 conversion kit' yields a link to the kit on Amazon... $42. http://amzn.to/1Dgwzie
If I were you, however, I'd certainly do a bit more detective work to make sure it will work for you. Good luck.