I have an 1200 sq ft ranch on a slab built about 1959 which has natural gas forced air heat delivered through duct work in the slab. My old furnace is getting tired and I was going to update to something more efficient and hopefully add central air at the same time but I'm finding this to be far more work and cost than I thought it would be going in. I'm told that I need to add a floor drain to get rid of moisture and that plumbing is over $3000, plus I need to upgrade my whole electrical system, another chunk of money that together with the Carrier hybrid heat & a/c system will put the project cost around $11,000 to 12,000, way out of my price range. I need to upgrade the electrical service & system regardless and am also upgrading the ceiling insulation to about R38 so that part I can accept. BUT is there anything I can do to get around ripping up the floor to get into the plumbing? Or should I just go with a new 80% furnace and make due with the ceiling fans that are in almost all rooms? Thanks from a new poster, Manny

If your furnace next to an outside wall? Might be some through the wall drain options. Or run the drain pipe horizontally to an existing drain.

Worse case, use mini-splits to get AC in some rooms.

I have found that AC condensate (distilled water) is no problem but the furnace flue condensate is very corrosive.

Corrosive, yes, but natural gas flue condensate it's not VERY corrosive (nothing as severe as oil-fired condensate).  NG flue condensate has a pH of ~5, only slightly more acidic than normal rainwater (pH ~5.6).  Neutral pH is 7.0, wine had a pH of ~3-4 (far more acidic than NG flue condensate).  Letting the condensate drip on metal or concrete will corrode it over time, but disposal into normal drain plumbing is just fine, using plastic impeller pumps & flexible plastic tubing.

The same li'l plastic pumps used for AC condensate get used for NG & propane condensate disposal all the time, eg: http://www.houseneeds.com/shop/HeatingProducts/HydronicHeating/pumps/condensatepumpbuypage.asp