Ive installed a bunch of systems and have my EPA 608 certificate. I know I can install it and have no issues, but I won't get the warranty. A highly reputable vendor that does work for my company quoted me at 7500 for a trane 14 SEER unit. My carrier oil furnace is not old, so I'm opting to keep it for back up heat or else I'd go to a higher SEER.