How Old Is My A.O. Smith Water Heater? Date Decoder

How Old Is My
A.O. Smith Water Heater?

How do I read an A.O. Smith serial number?

A.O. Smith, State and Reliance water heaters put the build date in the first four digits of the serial: year, then week. 1210A002243 was built in week 10 of 2012, early March. A serial that starts with a letter is the older format, generally used before about 2008.

By Jason Strauss, founder of Answer3 · Updated October 20, 2026

A.O. Smith Serial Number Decoder

How to Read the Serial Number

Find the rating plate on the side of the tank, usually above the gas control valve or the upper thermostat cover.

Digits 1–2 are the year.

Digits 3–4 are the week of the year (01–53).

If the serial starts with a letter, it's the older format, so the tank is likely more than 15 years old.

Serial	Built
1210A002243	Week 10 of 2012 (early March 2012)
1845A001234	Week 45 of 2018 (early November 2018)

A typical tank water heater lasts about 6 to 12 years. A tank in the second half of that range is worth budgeting for, especially if you see rust-colored water or moisture at the base.

Codes based on a week number give the month only approximately. If the plate prints a manufacture date (often labeled MFG or MFD), trust that over the serial.

How Long Does It Last?

Equipment	Typical service life
Tank water heater	6–12 years

Equipment

Typical service life

Tank water heater

6–12 years

Age doesn't mean a unit has to be replaced; it tells you when to start planning. A replacement you schedule costs less than one you buy the night it fails. If it's near the end of its range, write down the model, serial and capacity now, so a contractor can quote the right replacement without a trip just to read the plate.

Skip the decoding

Scan the nameplate and Answer3 Vault reads the serial, works out the age, saves the model and the maker's parts list, and reminds you before the unit reaches the end of its life.

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A.O. Smith Age FAQ

Do State and Reliance water heaters use the A.O. Smith code?

Yes. State and Reliance are A.O. Smith brands and use the same year-then-week serial format.

My A.O. Smith serial starts with a letter. How old is it?

That's the older A.O. Smith format, generally used before about 2008, so the tank is likely more than 15 years old. Check the plate for a printed manufacture date.

Where is the serial on an A.O. Smith water heater?

On the rating plate on the side of the tank, usually above the gas control valve or behind the upper element cover on electric models.

How Old Is My A.O. Smith Water Heater?