I have a Ducane Furnace, model number CMPE075U3. the previous owner had it switched to propane. there are orifaces sitting next to the furnace, they say 42 on them. i wanted to know what size orifaces i need to switch back to natural gas, and how to change them. thank you
The parts breakdown for that unit shows a #7 Orifice/Disc (that is no longer available) for the natural gas models. I looked at the CMPE 075 spec sheets and it gives a part number 20272002 (Allied Air) as the LP to NG conversion kit.
Don't forget that just changing the orifices may not be the answer, as springs were probably part of the LP kit as well.
Settle down! If you were that important, the city would give you lights and a siren for your car