All you need is a heater with the same capacity and similar BTU input. Bradford White has 50 gallon heater with 50,000 btu input, but it is not the one normally stocked. Other companies have similar units so it depends on who has a heater that meets your needs. A heater is at the "end of its expected life" when it starts leaking, whether that is after 1 year or 20. I do not replace a heater until it starts leaking, or has other major problems.