A.O. Smith Water Heater Age: Serial Number Decoder
A.O. Smith puts the build date in the first four digits of the serial number: the first two are the year and the next two are the week. That gives you an exact year, with no 20-year guesswork.
How old is my A.O. Smith water heater?
The first four digits of the serial number are the build date: the first two are the year and the next two are the week. Type your serial for an instant date, or read it by eye with the steps below.
e.g. Where's my serial number?
Standard A.O. Smith tank models use this code. Some specialty or non-standard units may use a different serial format.
Where to find your serial number
- Find the rating/specification label on the side of the tank, usually in the upper third of the unit.
- The serial number sits next to the model number; the first four digits are the date code (for example, 1210A002243).
- On tankless models, check the label on the front or side of the cabinet.
- State and American branded units (made by A.O. Smith) use the same first-four-digit date code.
How to read an A.O. Smith serial number
Rules last verified 2026-05-31Read the first four digits of the serial number. The first two are the year (20YY) and the next two are the week of that year (01 through 53). A single letter may sit in front of the digits. The week tells you roughly which month.
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Find the rating plate and serial number
Look for the rating label on the side of the tank, usually in the upper third. The serial number is printed next to the model number.
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Read the first two digits for the year
The first two digits are the year of manufacture. For example, 12 means 2012 and 18 means 2018. A single letter in front of the digits can be ignored.
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Read the next two digits for the week
The third and fourth digits are the week of the year, 01 through 53. Week 10 is early March, week 26 is late June, week 40 is early October. That gives you the approximate month.
Older / discontinued A.O. Smith serial formats
Mostly pre-2008, though some styles persisted into roughly 2008–2010. These older codes are letter-based and overlap, so treat the result as an estimate and confirm with A.O. Smith's official lookup.
| Serial example | How it decodes |
|---|---|
| AF04A093001 | Digits after the letters = year (04 → 2004); 2nd letter = month (A=Jan … M=Dec, skipping I), so F = June 2004. |
| GG03-1495366-S29 | Digits after the letters = year (03 → 2003); 2nd letter = month, so G = July 2003. |
| E07A135491 | 1st letter = month (E = May); next two digits = year (07 → 2007). |
| A20-H-78-015482 | 1970s style: digits between the hyphens = year (78 → 1978); 2nd letter = month (H = August). |
Worked examples
1210A002243 12 is the year 2012; 10 is week 10, which falls in early March. Built around March 2012.
S1318F000046 Ignore the leading S. 13 is the year 2013; 18 is week 18, in early May. Built around May 2013.
1836111786352 18 is the year 2018; 36 is week 36, in early September. Built around September 2018.
State, American, and the A.O. Smith family
A.O. Smith builds water heaters under many names. State and American branded tanks are made by A.O. Smith and use the same first-four-digit year-and-week date code, so this decoder works for them too. A.O. Smith also stands behind brands such as ProLine, Reliance, and U.S. Craftmaster. If your unit is an older private-label model and the first four digits are not a year and week, use the older-formats table above or the official A.O. Smith lookup.
What your manufacture date tells you
Warranty
Your build date sets the warranty baseline. A.O. Smith residential warranties run in tiers (commonly 6 or 10 years on many ProLine models; some lines differ) and generally start at the installation date. Enter your serial in A.O. Smith's Warranty Verification tool to see the exact coverage and expiration for your unit.
Check warranty by serial at A.O. Smith ↗
How long they last and when to replace
A.O. Smith's own guidance puts most of its water heaters at about 8 to 12 years, and suggests replacement is worth considering after 10 years if the unit leaks or runs erratically.
Home inspectors generally treat 10 to 12 years as the typical service life for a tank water heater, and many flag units past 15 years for replacement. (Industry guidance, not an A.O. Smith figure.)
Gas tankless units often last 15 to 20 years with descaling and good water quality. This is a general industry estimate.
Watch for these replacement warning signs:
- Age past 10 to 12 years. At or beyond typical tank service life; start planning a replacement.
- Rusty hot water. Discoloration from the hot tap can signal internal tank corrosion.
- Rumbling or popping. Noise usually means sediment buildup, which cuts efficiency and stresses the tank.
- Leaks at the base. Water around the base needs immediate attention and often means the tank is failing.
Why the age matters
A.O. Smith recalls and your serial
A.O. Smith recalled about 616,000 Ultra-Low NOx gas water heaters (30, 40, and 50 gallon) over a fire hazard, and the recall is keyed to the same first-four-digit serial code this page decodes. The burner screen can tear and let the burner throw excess radiant heat.
- Affected models
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30, 40 & 50-gallon gas Ultra-Low NOxSold as A.O. Smith / State / American / Kenmore / Reliance / U.S. Craftmaster / Whirlpool - Affected serials
- First four serial digits 1115 through 1631 — week 15 of 2011 through week 31 of 2016 (built April 8, 2011 to August 1, 2016). CPSC recall announced November 8, 2018.
- Hazard
- A torn burner screen can cause excess radiant heat and a fire if the heater sits directly on a wood or other combustible floor.
- Remedy
- Check your model and serial at waterheaterrecall.com for a free repair kit, or call A.O. Smith / State / Reliance / Kenmore at (866) 880-4661.
A separate 2005 recall of Robertshaw R110 gas control valves also covered A.O. Smith-family units (American Proline, U.S. Craftmaster, and others). Other older A.O. Smith recalls exist as well — search the CPSC site by brand if your unit falls outside the range above.
Read the official CPSC recall notice ↗ Recall list last checked 2026-05-31
Can't read the serial number?
If the rating plate is corroded, painted over, or missing, try these in order.
- If the rating plate is damaged, check a building permit, install sticker, or service tag for an installation date as a rough age.
- Use A.O. Smith's Warranty Verification tool with the serial number to confirm the build date and coverage.
- Contact A.O. Smith support with the model and serial number for help dating an older or private-label unit.
Model number vs serial number
The model number identifies the unit's size and configuration, not its build date. Only the serial number's first four digits carry the year and week. In many A.O. Smith residential model numbers a two-digit number indicates the nominal tank capacity in gallons, but confirm exact specs on the official spec sheet.
Frequently asked questions
How do I tell the age of my A.O. Smith water heater?
Read the first four digits of the serial number on the rating plate. The first two are the year (for example, 12 = 2012) and the next two are the week of that year. Enter the serial in the decoder above for an instant build date.
What do the first four digits of an A.O. Smith serial number mean?
The first two digits are the year of manufacture (20YY) and the next two are the week, 01 through 53. A single letter in front of the digits can be ignored. The week tells you the approximate month.
Where is the serial number on an A.O. Smith water heater?
On the rating/specification label on the side of the tank, usually in the upper third, next to the model number.
My A.O. Smith serial doesn't start with four digits. How do I read it?
Units made before about 2008 use older letter-based date codes. See the older-serial-formats table above for the common styles, or use A.O. Smith's official Warranty Verification lookup with your serial.
Is my State or American water heater the same as A.O. Smith?
Yes. A.O. Smith builds State and American water heaters, and they use the same first-four-digit year-and-week date code, so this decoder works for them too.
How precise is the date? Does A.O. Smith give the exact year?
Yes. Unlike brands that reuse a letter every 20 years, A.O. Smith's code gives the exact year plus the week, so there is no decade ambiguity.
Does A.O. Smith base the warranty on the manufacture date or the install date?
Residential warranties generally run from the installation date and come in tiers (commonly 6 or 10 years on many models; some lines differ). Use A.O. Smith's Warranty Verification tool with your serial for the exact coverage.
How long do A.O. Smith water heaters last?
A.O. Smith's own guidance is about 8 to 12 years for most of its water heaters, with replacement worth considering after 10 years. Tankless units often run 15 to 20 years (general industry estimate).
Does the model number tell you when an A.O. Smith was made?
No. The model number describes size and configuration. Only the first four digits of the serial number carry the year and week.
Is it worth repairing an A.O. Smith that is 10 to 15 years old?
Past 10 to 12 years a tank is at typical end of life, and the risk of failure climbs after 15. Weigh the repair cost against the unit's age and any signs of corrosion or leaks.
Sources & verification
The serial and date-code rules and examples are sourced below — from manufacturer and inspector references — with recall data from the CPSC. Edge-case formats and broader context (lifespan, inspection, insurance, code) are separately sourced too. Confirm an individual unit with the official lookup.
Documents the modern first-four-digit year+week format with examples (1210A002243 = 2012 week 10), the legacy letter-based styles, and the A.O. Smith brand family (State, American, ProLine, Reliance, and more).
Official A.O. Smith tool/guidance: the manufacturing date is read from the serial number's leading digits (year then week).
Official tool that returns warranty status and coverage from the water heater's serial number.
Confirms A.O. Smith has used the YYWW (year + week) serial date format since about 2008.
~616,000 30/40/50-gallon gas Ultra-Low NOx water heaters built Apr 8 2011–Aug 1 2016 (serial first-four-digits 1115 through 1631) recalled for a burner-screen fire hazard (recall announced Nov 8 2018); sold under A.O. Smith, State, American, Kenmore, Reliance, U.S. Craftmaster, and Whirlpool. Check model+serial at waterheaterrecall.com. Recall hotline differs by brand: American/Whirlpool/U.S. Craftmaster 866-854-2793; A.O. Smith/State/Reliance/Kenmore 866-880-4661.
2005 recall of Robertshaw R110 gas control valves (made July 25 to August 14, 2005) installed on water heaters from many brands (including Bradford White and A.O. Smith-family units); broken valve screws could leak gas (explosion/fire risk).