DW wrote:
Both elements are never on at the same time. And with utility power
running through it, it has never thrown the breakers. Hope this helps

Depends on how it may be wired. Many water heaters have the option of
having both to come on independently which means that can be on at the
same time. Most come factory wired in cascading operation where one is
off when the other is on.

That can mean the difference of 4500 watts or 9000 watts. Of course if
not wired can be for the latter operation so that only 4500 watts would
be needed at any time.