Hi everyone. I'm new here so sorry if this has been discussed before. I have just gotten quotes to replace my old gas furnace (and tempstar AC unit)with some new 80% trane or carrier models. I am trying to figure out what my monthly savings for heating will be after getting a new model. I know that my old unit is terrible, its an early 80's Carrier super saver gas furnace, I think the model number is 58ssb0802c. Does anyone know roughly what the effieciency of an older model like that would be? I am also replacing the original westinghouse mercury thermometer from 1964 lol....so I think I will be saving at least about 100 bucks a month year round. If it matters, our house is about 2000 square feet and we live in Maryland. Thanks for any help!