I didn’t have mine replaced but very recently had some minor repair work. Asked about what it would/will cost to replace my furnace (from 2007, in a 110 year old Shadyside home, probably in the next 5-7 years) and was told $3500ish all in for full replacement parts and labor. The HVAC person is a very good contact and friend via my wife’s former work as an East End property manager. We’ve used him for years and he’s always been beyond responsive and fair to us, so I assume this is a very reasonable cost estimate