Hello, I am new to this subject and need some advice. I have a house with a Heil 9000 forced air gas furnance. I recently had some work done on the furnace, and the contractor stated that it was at the end of its useful life and needed to be replaced. How long does a furnace like that last? The house was built in 1992 and was @ 2600 square feet. I just finished he basement and it is about 4000 square feet now. I was thinking about replacing the furnace and putting in central a/c at the same time. I also have a question about that! Does a/c take different duct work, or can it be put in using the same system the furnace uses. Thanks you for any help, this is my first house and I am very confused!