The quick and dirty:
I live in Atlanta
House built in 79.
2 Stories (2nd story is half as big as first story)
On a slab.
It has 2 behemoth furnaces in the attic and 2 AC units outside.
All units are original material - 26 years old.
Heating bills: $ 375 - $ 475 /mo
Cooling: Maybe $ 100 less than that
I have been talking to other clueless homeowners like myself about their bills. They have all kinds of wild reactions when I tell them mine.
I have decided to replace my current system(s). I have read here and there that it's smarter to "service" current units until they die, rather than replace them. My math causes me to draw a different conclusion.
I don't know why I have 2 of everything. It seems crazy to me. And, my suspicion is that if I replace them with one furnace and one AC unit, the Higher Power of your choice only knows how much duct reworking will have to be done.
If I want to replace my current albatrosses what kind of trouble am I going to run into ? Am I crazy to think that I shouldn't have 2 of everything ? Would you imagine that the ducts will be a major thing ?
What else do you think and what else would you advise ?
I see that you guys are looking at it.
Have I asked the wrong kind of question ?
2 stories need 2 units. odds are your systems are over sized and improperly installed. get a qualified contractor to do a load calculation, and take a look at your duct work.
Many houses have two furnaces and A/C, it depends on the size. All I know about your house is that it was built in 79, 2 stories, and upstairs is half as big as lower level. You are correct that the duct system would have to be changed to go to a one unit system, and most likely wouldn't be worth it. You should find a good contractor in your area and have them come out and let you know what your options are.
I agree the units are probably oversized. Best thing to do is get someone to give you a qoute for a new system. Better yet, get three quotes and see what the different contrators recommend. Make sure they do a heat loss and heat gain. My recommendation with out looking at it would be to stay with two systems. Their are many advantages to having two systems like more consistent temps through out the home. If you spend more time on one floor of the house you can set the other system back so it cylces less often. Also if one system fails you have a back up heat or air because you know that one will fail on a holiday or after hours.