This is a very common question. Most of the tanks we are replacing now are in the 10 year range. We are even replacing slightly newer tanks.
We recommend you consider replacing your water heater if it is 10 years or older. Its not a bad idea considering they only start leaking on weekends, evenings and Christmas Eve! You can save a significant amount of money and frustrations by simply booking a tank replacement on regular time.
Here is a few common manufacturers serial number date codes that may help you decide on the age of your water heater if you don’t already know.
John Wood: First two number in sequence are the year, second two are either the month or week. The second number will not matter as much because you are concerned mostly with the approximate year of the water heater.
Rheem: Rheem uses the first two digits for the month and the second two digits for the year.