Don't forget 110.3(B) mfrs instructions.Where you get that from? It draws nearly the same amps as 4500 watts does @ 240 which is allowed to be on a 30 even though 25 is next size higher after factoring 125%. I believe this kind of load is allowed to be on circuit of up to 150% of rated amps, which is why it is common to see 30 amp breaker for 4500 watt at 240 even though 25 will work, either case 10 AWG conductor is still needed.
You can get a 208V element for waterheaters so they are still 4500W.
For a busy house with teenagers I prefer the 50 gal with the 5500W element at 30A.
You can even get a single phase 480V element.
![waterheater-smaller.jpg waterheater-smaller.jpg](https://forums.mikeholt.com/data/attachments/15/15322-3522546ca6de976c11d7a80144f6b3b5.jpg)