How old is my State water heater?

By Dana Whitlock. Updated October 2026. Widely documented.

On a State tank, C05 means March 2005 and 0912 means the twelfth week of 2009. Tanks made in 2008 or later begin with four digits, year then week. Older ones begin with a month letter and a two-digit year.

State sits in the A.O. Smith family, and the two brands share their date codes. This is a Widely documented format. The parent company has confirmed the year-and-week rule in recall paperwork, and utility and inspection references agree on the older month-letter style, but State does not post a decoder of its own.

Where to find the label on a State water heater

Find the data plate on the front of the tank, close to the gas control on a gas unit or the upper thermostat cover on an electric one. It lists the model, the serial and the input rating. In a dim garage or basement, a flashlight held off to one side cuts glare on the plastic label. Leave all covers in place; reading the plate never requires opening anything, and an electric tank's covers protect live terminals.

How to read the code

Two layouts cover nearly every State tank you will find in a house. Newer layout: four leading digits, where digits one and two are the year and digits three and four are the production week (01 to 53). Older layout: a single letter, then a two-digit year. The month letters go in order A through M with no I, so A is January, H is August, J is September and M is December. Recall records for State's GS6 75-gallon gas model list serials starting L07A and M07A, which are November and December 2007 builds.

Real serials in this code

When the format changed

State moved from the month-letter code to year-and-week around 2008, at the same time as A.O. Smith. Tanks from the first half of 2008 can carry either style, so let the first character decide: a letter means month code, a digit means year code. The month-letter code itself has one quirk. A few older charts say J stands for October; the federal recall lists for this family show I is skipped and J is September, so the decoder follows that. When the age matters for a warranty claim, State's warranty verification page will return the coverage status for your serial.

Who makes State

State is an A.O. Smith brand and appears on the company's brand list next to Reliance, American and U.S. Craftmaster. Reliance tanks, and Kenmore tanks that State built, used the same single-letter month code before 2008. A.O. Smith's own tanks share the year-week code that State uses now. If you own a State and a Reliance in the same building, one decoder rule set reads both.

How sure is this?

Widely documented. State doesn't publish this code; it comes from recall notices, service literature and inspector references. We tested the ao smith rules against 34 serials, 32 of them with a date known from a recall notice, a printed label date or the maker. None decoded to a wrong year; codes whose year mark repeats show every possible reading. Always confirm with State's serial lookup before you spend money on the answer.

Quick notes

• A serial that begins with a digit is the newer code. The first two digits are the year.
• A tank with a C05-style code is now about 20 years old, older than DOE's average gas tank life of about 14.5 years.
• Keep a photo of the plate. State's warranty and registration pages ask for the full serial.
• If the plate is too faded to read, the model and serial are often repeated on the original carton label or the installer's invoice.