So our water heater has been showing signs of failure lately: changing water temperatures, water not getting as warm as it used to, etc. I did some digging and found that (at least this brand) the serial number can be decoded to determine the age of the water heater. Who knew? Not me, anyways. The decoder was found on the website, complete with an example (which is always helpful for decoders):

Here is the label that is on our heater, which puts ours as being manufactured in October of 2006 (which is kinda old, apparently – again, who knew? Not me!):