Had our furnace serviced today, and the tech said it has hairline cracks in the heat exchanger. He said they are not big enough to have to shut it down today, but within a year they could be. He recommends a new furnace. The current one is a 1999 Payne. Do you have any recommendations of who I could bring in to verify that the cracks are actually there (someone who doesn't have an interest in selling me a new furnace)? Does it seem logical that a unit that is only 10 years old would have this problem already?