if the furnace installed is new and comes with a specific # of years warranty I would check with the company and see if the warranty starts from the date of install or some other date...explaine your situation clearly and see what they say...also is it the correct efficiency rating as was quoted you and the model quoted you.... is the installer a dealer for the furnace company or just a HVAC company picking it up at a local distributor...is it dented any where
Sorry about that-- I see part of my question was inadvertently left off...
Is it standard to install a furnace that is 4 years old (furnace manufactured 4 years ago) in a newly constructed custom home and sell it as a new furnace?
That is pressing it. Most distributors would not have inventory that stale. It is possible that a contractor had one "in the back room" that he bought on spec or anticipation of a job, then didn't use it. I would think that as long as it is new, it should be ok. But somewhere there should be a discount on a 4 year old model;