Gas Furnace Question
I'm looking at getting a high efficiency furnace to replace my ancient unit. I'm looking to go high efficiency, mainly because I plan on re-roofing my house and I want to do away with the chimney. Anyway, I found a good deal on a used one, it's a Carrier Model GNJ075N12D2 91% AFUE, but it's been converted to propane. How hard is it to change it back to natural gas? Also, the guy says the sticker says that it has an Input of120,000 BTU and an Output of 112,000BTU, but I've tried to search that model number and the only thing I've found listed it as a 75,000 BTU furnace. My house is a 90 year old 1300 square foot 1.5 story house with a basement. I just re-insulated and resided the whole house, so that shouldn't be an issue. I'm just wondeing if that furnace is properly sized, or is it overkill.