Steve - This advice is my own personal experience with different furnace/AC units. I am referring to both HVAC and home units. My sister and brother-in-law have 3 restaurants, one has (2) 20 year old carrier units which very rarely require maintenance. We manage to keep up a pretty good scheduled p.m. on them. There is also (1) York unit on the roof that is very dependable as well. Keep in mind that most Carrier furnaces/AC have proprietary parts - They cost about 2-3 times more then generic parts. They are good units in my opinion. The other restaurants both have TRANE units - Both are less than 5 years old and have been serviced way, WAY to much. One company actually had a joke. One thing can only stop a TRANE, The Weather!!! Anyhow, because of these units reliability, I will never purchase one for myself and highly discourage others. I have a York AC system in my home - although it is only 3 years old. No service yet and YORK has a good reputation. I have a comfortmaker furnace that I would not recommend - It is very loud. My brother has a lennox, 8 years old, no problems ever and very quiet. My sister and brother-in-law have both Carrier furnace and AC - 10 years old, no service calls. Just had to replace the fan motor on top of the AC last summer - again, nothing but a carrier part will fit. The furnace is very dependable and low noise. My parents have a Janatrol AC, 15 years old - no service calls ever. The furnace is an Air-Ease, oil fired and other than a scheduled filter/nozzle replacement, and a transformer on the injector pump - no problems and it is 20+ years old as well. I hope this helps. I saw your post and saw TRANE... Remember the only thing that stops one is the weather! Best of luck.