I am looking to change my thermostat to a digital one. Propblem is, I don't know what to get. I don't know to get one for a heat pump, or central heat and air, If they both heat and cool with indoor and outdoor units, how do you know what I have? I have seen some thermostats for 2 stage systems, what is that? What I have is a Trane, there is an outdoor unit, and an indoor unit. The thermostat is mechanical and when its on heat there is two lights, if its cold enough out the blue "aux heat" light comes on, then there is a red "emergency heat" light. Does that mean it's a 2 stage heat system? I have seen a lot of digital thermostats on eBay, but some say they won't work for heat pumps, and some are for 2 stage, I just don't know what to get. Any help would be greatly appreciated.