20 yr old American Std Heat Pump stopped working. Load rating when home was built was a 3 ton unit. A 3.5 ton 12 seer was installed. 1,987 sq ft. One level in Clover SC on the lake. warm humid summers, mild winters with occasional weeks with temp below 30* Considering Trane, American Std, or Carrier. want a reliable system, good track record. the information is overwhelming when I look at brochures and online. On a fixed income...Natural gas is available on our street now. I need a good efficient system. Husband is not able to help with decision process. I've seen info on Trane XR15 or XR16, Amer Std Gold XI 15 & 16. I need sound advice on best options for our home.