How old is this pool heater model number E-00398026?

To determine the age of the pool heater model number E-00398026, you typically need to check the manufacturer's date, which is often found on the unit's rating plate or in the user manual. If that information is not readily available, you may also contact the manufacturer directly with the model number for assistance. Without specific details from the manufacturer, it's difficult to ascertain the exact age of the heater.