I had a Heil gas furnace installed that will be primarily used for a/c but it does have a heat too, Model N8MSN0701716A1. I installed the electrical with a 20 amp breaker/ 12-2 wire as per HVAC installer instructions. After searching online electrical data it calls for a 15amp breaker/14-2 wire, max. unit amps 9.5. It also says max. wire length 29ft. I have the furnace installed in my attic so I'm running close to 40 ft. of wire from the basement panel to attic. I'm really sweating this and was hoping I'm ok with the 20amp breaker/ 12-2 wire. If what I went with is really a no no I guess I can rip it out and start from scratch but I was hoping I would be ok. I would appreciate your expertise. Thanks in advance!