Homeowner here who is not familiar with hvac and is remodeling and needs to relocate and replace 15 year old Ruud 48000 btu furnace connected to Trane XL1200 (1995) compressor. This is for the first floor (1500sf) and crawl space is deep enough for undermounting. I have a newer 80,000 btu unit in the attic, connected to another Trane XL1200 for the second floor, 1500sf also. I am in Dallas so cooling is more of a factor than heat. My house is well insulated, average number of double pane windows. Would going undermount in the crawlspace be my best option budget wise versus the attic? Could the existing attic unit be used to heat both floors and still use both compressors for cooling? Chase space is available from the crawl space to attic, crawl space is available under the entire first floor (4ft min). Should I consider an outside unit? Thanks for any advice.