Yep Nat. gas isn't as good as LP FYI One cubic foot (ft3) of natural gas contains 1,030 BTUs and one cubic foot of propane gas contains 2,516 BTUs, giving propane about twice the energy content of natural gas.
Never realized they were that different. I have seen for gas grills and forklifts where they require different part though. So I would guess it would be available for a furnace. Maybe as simple as calling a good HVAC guy out.
