State water heater age by serial number
The serial number is on the rating plate attached to the tank. On a State water heater built since 2008, the first two digits of the serial are the year and the next two are the week. Older State serials start with a letter for the month.
Decode a State serial number
How to read a State serial number
State has used 3 serial formats. Find the one that matches the shape of your serial.
Year and week, first four digits
Skip a leading letter if there is one. The first two digits are the year and the next two are the week of that year.
Shape: four digits, then a letter and six digits, or nine more digits. Some serials carry one extra letter in front.
1210A002243 reads as week 10 of 2012 (around March).
Month letter, then two-digit year
The first letter is the month, A for January through M for December with the letter I left out. The two digits after it are the year.
Shape: one letter, two digits, then a letter and six digits or six to eight digits.
E07A135491 reads as May 2007.
Month letter
- A January
- B February
- C March
- D April
- E May
- F June
- G July
- H August
- J September
- K October
- L November
- M December
State and Reliance used this layout for decades. A. O. Smith-branded heaters carry it only from July 2004, when the leading factory letter was dropped, to 2007.
Factory letter, month letter, two-digit year
The first letter is the factory. The second letter is the month, A for January through M for December with the letter I left out. The two digits after the letters are the year.
Shape: two letters, two digits, then more digits. Older plates print it in hyphenated groups.
GG03-1495366-S29 reads as July 2003.
Month letter
- A January
- B February
- C March
- D April
- E May
- F June
- G July
- H August
- J September
- K October
- L November
- M December
Where to find the serial number
The rating plate is on the outside of the tank jacket. On gas models it is next to the gas control valve.
Newer plates print a build date under the serial number. When it is there, read it directly.
If the serial number does not decode
- The small print at the bottom of the plate names the company that built the heater. Store brands changed makers over the years.
- State built heaters for many store brands. A heater with a State serial reads the same way whatever name is on the jacket.
- The manufacturer can confirm the date from the serial: State registration, warranty or serial lookup.
What the age tells you
| Equipment | Typical service life |
|---|---|
| Tank water heater | 10 to 15 years |
| Tankless water heater | about 20 years |
About State
State Industries started in Nashville, Tennessee in 1946 and built water heaters for many store brands, Reliance and Kenmore among them. A. O. Smith bought the company in 2001. State kept its own month-letter serial for several years after the purchase.
Brands that share this serial system: A. O. Smith, Reliance, Kenmore.
Questions and answers
Which characters in a State serial number show the date?
Skip a leading letter if there is one. The first two digits are the year and the next two are the week of that year. This applies to units built since 2008.
Why does my State serial number look different?
State has used 3 serial formats: year and week, first four digits (built since 2008); month letter, then two-digit year (built until 2007); factory letter, month letter, two-digit year (built until mid-2004). The decoder tries each one.
Sources
- A. O. Smith Canada: frequently asked questions, reading the serial number (manufacturer): https://www.hotwatercanada.ca/faqs/
- A. O. Smith International: manufacturing date of a device (manufacturer): https://aosmithinternational.com/manufacturing-date-device/
- CPSC recall 19-029: A. O. Smith ultra-low NOx water heaters, serial ranges by build date (US Consumer Product Safety Commission): https://www.cpsc.gov/Recalls/2019/A-O-Smith-Recalls-Ultra-Low-NOx-Water-Heaters-Due-to-Fire-Hazard
- Building Intelligence Center: A. O. Smith water heater age (independent reference): https://www.building-center.org/a-o-smith-water-heater-age/
- CPSC recall: A. O. Smith, State, Reliance, Maytag and Apollo water heaters, serial prefixes by month (US Consumer Product Safety Commission): https://www.cpsc.gov/Recalls/2005/cpsc-ao-smith-recall-of-water-heaters
- CPSC recall: A. O. Smith gas water heaters, serial ranges for units sold November 2007 to January 2008 (US Consumer Product Safety Commission): https://www.cpsc.gov/Recalls/2008/ao-smith-recalls-gas-water-heaters-due-to-fire-and-carbon-monoxide-hazards
- Building Intelligence Center: State water heater age (independent reference): https://www.building-center.org/state-water-heater-age/
- CPSC recall: A. O. Smith gas water heaters built April to July 1991, serial prefixes MD91 to MG91 (US Consumer Product Safety Commission): https://www.cpsc.gov/Recalls/2012/certain-30-and-40-gallon-ao-smith-lp-and-natural-gas-water-heaters-voluntarily-recalled
- InspectAPedia: A. O. Smith water heater age (independent reference): https://inspectapedia.com/plumbing/AO-Smith-Water-Heater-Age-Manuals.php
Formats last checked against these sources on October 5, 2026. Found a serial that does not fit? Send a correction. How formats are verified: method and sources.