Hola... like others, google search brings up this thread near the top, so kinda resurrecting. Abraham can probably tell you more about code (I live in the Atlanta area too), but I went with Navien NR-210A because of the costs and research.
1) house was built in 1993, fist owner. It still has the original A.O. Smith 40gal HWH tank. I've NEVER serviced it and barely even glance at it; however, 17yrs old got me to do some research. First, my bet is that the bottom will dump soon. It's isolated, so I don't believe much damage will happen. Second, it's terribly inefficient by todays standards. I run out of hot water quicker and it takes awhile to get any back. Since it was built in 1993, the codes were different. For me to install a new tank HWH would require the company to install a square cement wall around the unit and deepen the ditch (it's in a "half" crawl space with 6' height). The existing unit is 48" and newer units are taller. BLUF: to replace with a .7EF HWH, 12yr warranty, do the install with construction will cost me about 3k and no 30% Fed Credit.
2) for 3.3k, I get a new Navien NR-210A (bells/whistles), .98EF and installation of circulation T's at the long runs on external circulation, 15/5yrs warranty ... and the 30% Fed Credit. To me it was no brainer. More efficiency, less cost overall after credit.
My math:
Standard tank: 3000.00
Tax Credit: 0.00
TOTAL: 3000.00
Tankless: 3300.00
Tax Credit: 990.00
TOTAL: 2310.00
Delta: 690.00 savings going tankless, + reduced gas costs.
Anyone see anything wrong with my math?