Find the rating plate
Every tank water heater has a rating plate: a label on the side of the tank with the model number, the serial number and the gas or electrical ratings.
| Brand | Where the maker says to look |
|---|---|
| Bradford White | On the rating plate on the water heater, which shows the model number and serial number |
| A.O. Smith | On the data plate next to the gas control valve/thermostat (gas models, per CPSC notices); A.O. Smith’s Lowe’s line says the label is near the bottom of the heater |
| State | On the nameplate on the side of the unit |
| GE (Rheem-made tanks) | On the side of the unit, right or left |
Basis: official (Bradford White FAQ, CPSC recall 19-029, A.O. Smith at Lowe’s, State and GE support pages). Don’t remove covers or panels to reach it: on gas models the plate sits beside the gas control, and on electric models the access panels hide wiring.
Photograph the whole plate. The serial number gives the date; the model number is what you need for parts, manuals and recall checks.
Water heater serial number lookup by brand
The checker above decodes all of these. Here is what it reads for each brand, including A.O. Smith (often searched as AO Smith):
| Brand (and brands sharing the code) | How to read the date | Example |
|---|---|---|
| Bradford White | 1st letter = year, 2nd letter = month (A–M, no I); the year letters repeat every 20 years | DH9477405 = August 2007 |
| A.O. Smith, State, Reliance (from about 2008), American (before 2008 too) | First 4 digits = year and week | 1210… = 2012, week 10 (March) |
| A.O. Smith, State, Reliance (before about 2008–2010) | Month letter (A–M, no I), then a 2-digit year | L07… = November 2007 |
| A.O. Smith (before about mid-2004) | Two letters: the 2nd is the month, then a 2-digit year | MD91… = April 1991 |
| Rheem, Ruud, Richmond, GE tanks made mid-1999 to about 2016 | First 4 digits after any letters = month, then year | RH 0806B17262 = August 2006 |
| Whirlpool, Kenmore (from about 2008) | First 4 digits = year and week | 1104T403904 = week 4 of 2011 |
| Rheem family (some plants from 2012) | Plant letter, then week, then year | M141209135 = week 14 of 2012 |
| Lochinvar tanks (from 2011) | First 4 digits = year and week | 1142N012345 = week 42 of 2011 |
| Lochinvar tanks (1979 to 2011) | 1st letter = year, 2nd letter = month (same letters as Bradford White) | KJ-1000130 = September 1993 |
| Navien (tankless) | Characters 6–10 = year, month (1–9, X = October), day | 7414C14X1771143 = October 17, 2014 |
| Rinnai (tankless, from about 2009) | 1st letter = year (A = 2009 … Z = 2029), 2nd letter = month | NK.CA-129326 = October 2021 |
| Rinnai (older) | Year, then month, in digits | 04.03-102521 = March 2004 |
Basis: official (Bradford White date code chart; CPSC recall 19-029 for A.O. Smith’s year-and-week code; Rheem Technical Service Bulletin 1207 and rheem.com; Lochinvar’s serial guide; CPSC recall 19-057 for Navien; for Rinnai, a service manual section headed “Water Heaters and Direct Vent Furnaces” whose text refers to furnaces, backed by industry references), with examples from CPSC recall notices, the makers’ documents and inspection references. Each brand page shows the full tables and how we checked them: Bradford White, A.O. Smith and State, American, Reliance, Rheem and Ruud, Whirlpool and Kenmore, Lochinvar, Navien, Rinnai.
Other brands. Other tankless brands, heat pump models and brands not listed here use other codes. Read the date printed on the rating plate, or ask the maker’s support line with the model and serial number.
If the plate prints a date
Some newer rating plates print the manufacture date outright. Rheem’s 2012 bulletin says its new rating label, used from April 2012 at its Mexicali plant and June 2012 at Nuevo Laredo, shows the date of manufacture on the third line. A printed date always beats a decoded one.
Printable cheat sheet
Water heater age cheat sheet (PDF, one US Letter page): where the rating plate is, the date codes for Bradford White; A.O. Smith, State, Reliance and American, plus Whirlpool and Kenmore heaters built by A.O. Smith companies; Rheem, Ruud, Richmond and GE; and Lochinvar, Navien and Rinnai, plus typical lifespans, a form to record the plate and what the age means. It prints on standard US Letter paper with no settings to change. Free to print, share or hand to clients unchanged.
How the age compares with a typical lifespan
Our summary: a tank water heater typically lasts about 11 years; most published figures fall between 8 and 15. That’s the figure the checker compares your heater’s age with. Tankless heaters are usually given about 20 years (US Department of Energy; ENERGY STAR). Every figure, by source and heater type, plus what shortens a heater’s life and the signs one is near the end, is on how long do water heaters last?
What the age means
- Under about 8 years: early to middle of a typical tank’s life.
- About 10 years or more: Bradford White says that if a water heater is more than 10 years old, “it makes sense to consider replacing it now, before you notice any problems.” Rheem says “the risk of leaks and sudden failure increases significantly after 10 years.” DOE’s Energy Saver guide advised starting to research a replacement as a heater nears 10 to 15 years.
- Past about 15 years: older than even the longer published figures.
These are averages, not a prediction for one heater. Buying a house? Note the heater’s age in your inspection notes; it helps you budget. What a home inspector, a permit inspector and a plumber each check is on our water heater inspection page.
Planning a replacement? See what a new water heater costs installed. Hot water slow to come back? Check how long a water heater takes to heat up for gas, electric, heat pump and tankless models.
Limitations
- The serial gives the build date, not the install date or how the heater has been used.
- Some codes repeat (Bradford White’s letters every 20 years; old 2-digit years every century), so check the plate for a printed date or ANSI standard year, and use common sense about how old the heater looks.
- For US A.O. Smith and State heaters, the official statement of the year-and-week code is CPSC’s recall notice covering 2011–2016 production; CPSC’s 2018 Lowe’s recall (serials 1805–1809) fits the same code. A.O. Smith’s own page describing it is on its European site, so we treat that only as supporting evidence. The switch from the older letter code happened around 2008 to 2010; we couldn’t find the exact date.
Checked against the sources below on 30 September 2026; sources added or changed on 6 October 2026 were checked that day. The rating-plate diagram and lifespan summary were checked on 11 October 2026.
