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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.
Thanks,
Corey
 

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075 = 75,000 BTU's. What is the serial# and how old is it. Used furnaces are scary as it could have a bad heat exchanger and you buy some expensive scrap metal. Needs new manifold orifices and a conversion kit for the gas valve and a tech to install them and set it up properly and safely.
 

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Discussion Starter #3
It came out of a house that was bought by the city and being torn down to expand the hospital, and the seller is offering a guarantee, so I'm not too worried about it being no good. I think the serial number is 6001E15017, but I didn't get a very good look at it. As far as I know it's only a couple of years old. It pretty much looks brand new. So what should one expect to pay to have it converted back to natural gas?
 

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Looks like a 2001 model. Cost depends on whether the gas valve can be converted back to nat.gas or needs replacing, plus the price of the orifices etc. You may want to phone some local Carrier dealers for a price. I would guess 2-3 hrs labor at $85/hr or more. Gas valve and orifices $400-600.
 

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Hope its not one of the cariers under recall.

Probably over sized for your 1300 sq ft, even though it is only 75,000 BTUs.
 

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Secondary heat exchanger problems.

Call the local Carrier distributor. They'll need model and serial number.

But, doubtful you'll be able to take advantage of the recall on it.
 
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