My furnace shut off this weekend. The house was built in 1989 and furnace is only 14 yrs old. There are cracks in heat exchange and needs to be replaced. I am opting for 80% efficient. The furnace in house now is York. The duck work for the flues have several 90 angles and is also causing problem for ventilation. Furnace guy wants to use Trane XR80 Single Stage. Any feedback on this furnace? Also, would you do entire new furnace or just replace heat exchanger?