We live in Atl area so mild winters. We have 2 a/c units on ranch home 2800 sq ft. We currently have a gas furnace working fine. One a/c unit is out and a friend gave us a less than 1 year old Am Standard heat pump/ac with air handler. They needed a bigger unit anyway I have gotten several configurations. The current furnance is in the attic & they proposed connecting new handler in the attic for just heat pump (most expensive) or putting air exchange outside with dual fuel less expensive or using furnance I have now and changing the coil on it and using as dual fuel and not using the new air handler at all?? I am confused like I said our furnance is about 15 years old but working fine and we would like to use the heat pump since it kind of landed in our lap and the furnance is getting older. Any help please??