A. O. Smith water heater age by serial number (State, American, Reliance)
On A. O. Smith, State, Reliance, American and U.S. Craftmaster water heaters, the first four digits of the serial number are the date: two digits for the year, then two for the month on units built before 2008 or for the week on units built after 2008. Skip a single letter at the start if there is one. The decoder applies that rule and shows both readings where 2008 leaves it open.
Where the serial number is
The serial is printed next to the model number on the label of the tank jacket. A. O. Smith Canada's own example, U0106413635, shows the typical shape: one letter, then the digits that carry the date.
One rule for several brands
A. O. Smith bought State at the end of 2001 and completed the purchase of GSW, the owner of American Water Heater and U.S. Craftmaster, in 2006; Reliance is also its brand. For units made between 8 April 2011 and 1 August 2016, a U.S. recall names A. O. Smith as the maker of Whirlpool and Kenmore water heaters too. Since the serial looks the same on all of them, the decoder reads its shape, but the brand you choose still matters for Whirlpool and Kenmore.
Year and month, then year and week
A. O. Smith Canada explains the rule on its FAQ page: skip a letter at the start, then the first two digits are the year. The next two digits are the month for units built before 2008 and the week for units built after 2008. Its example, U0106413635, is June 2001. A. O. Smith's international site gives a recent example: a serial starting 2037 was built in week 37 of 2020, between 7 and 13 September.
What the 2018 recall confirms
CPSC recall 19-029 (November 2018) covered Ultra-Low NOx gas heaters sold as A. O. Smith, American, Kenmore, Reliance, State, U.S. Craftmaster and Whirlpool. It states that the first four digits are the year and the week, and it lists serials 1115 to 1631 as built from 8 April 2011 to 1 August 2016. The two sets of dates agree, which makes this the strongest evidence for the year-and-week reading.
Letter codes of 2004 and 2005
A 2005 recall of 75-gallon propane heaters (CPSC 06-002) shows a different form on A. O. Smith, State and Reliance units: a month letter followed by the year, sometimes preceded by M or A. G04 is July 2004, M04 is December 2004, and MA04, AA04 and A04 all mean January 2004. The decoder applies this form only to those three brands and those two years.
How to read the plate, step by step
- Drop a single letter in front of the first four digits, if there is one.
- Read digits 1 and 2 as the year.
- Read digits 3 and 4 as the month if the year is 2007 or earlier, and as the week if it is 2009 or later.
- If the serial starts with a letter from A to M followed by 04 or 05, the 2004-2005 letter form may apply as well; the decoder lists both readings when both fit.
Serial formats the decoder reads
| Format | How it is read |
|---|---|
| A. O. Smith year + month (before 2008) or year + week (after 2008) | A. O. Smith family: skip a leading letter; digits 1-2 are the year. A. O. Smith Canada states that digits 3-4 are the month for units made before 2008 and the week for units made after 2008. CPSC recall 19-029 confirms year + week for 2011 to 2016 across A. O. Smith, American, Kenmore, Reliance, State, U.S. Craftmaster and Whirlpool. |
| A. O. Smith 2004-2005 month letter + year | 2004-2005 letter form from CPSC recall 06-002: an optional M or A, then a month letter (A = January to M = December, I skipped), then the two-digit year. |
Worked examples
Each serial below is either printed in a source or built by us strictly by the source's rule (marked "by the rule"), and each is an automated test of the decoder. Readings that depend on today's date are as of October 27, 2026.
| Serial | Result | Why |
|---|---|---|
| 1115123456A. O. Smithfrom a source | week 15 of 2011 (about April)Decoded | CPSC recall 19-029 covers serials 1115 to 1631, made from 8 April 2011: week 15 of 2011. |
| 1631123456Whirlpool (2011-2016)from a source | week 31 of 2016 (about July)Decoded | The end of the recall range (made up to 1 August 2016), here as a Whirlpool unit inside the confirmed window. |
| 1712345678Kenmore (2011-2016)by the rule | Not confirmed by the manufacturer | Read by the A. O. Smith rule this is week 12 of 2017, after the window in which A. O. Smith is confirmed as Kenmore's supplier. |
| 2037123456A. O. Smithfrom a source | week 37 of 2020 (about September)Decoded | A. O. Smith International's example: a serial starting 2037 was made in week 37 of 2020 (7 to 13 September). |
| U0106413635A. O. Smithfrom a source | June 2001Decoded | A. O. Smith Canada's example: skip the U, then 01 06 = June 2001. |
| G045012345Statefrom a source | July 2004Decoded | CPSC recall 06-002 lists serials starting G04 as July 2004 (the digits after G04 are ours). |
| MA04123456A. O. Smithfrom a source | January 2004Decoded | CPSC recall 06-002: MA04, AA04 and A04 all stand for January 2004. |
| G041234567Relianceby the rule | December 2004 or July 2004Two possible dates | Both documented rules fit: skip the G and read 04 12 as December 2004, or read G04 as July 2004. |
| 0806123456A. O. Smithby the rule | June 2008 or week 6 of 2008 (about February)Two possible dates | 2008 is the year the rule changes from month to week, so 06 can be June or week 6. |
| 0128104380Americanby the rule | Not confirmed by the manufacturer | For 2001 the documented rule reads digits 3-4 as a month, and 28 is not a month; a year + week reading for 2001 rests only on an inference from a recall notice. |
Edge cases and limits
- A. O. Smith Canada only says "before 2008" and "after 2008", so for a 2008 serial digits 3 and 4 can be a month or a week. The decoder shows both unless the number is above 12, in which case it can only be a week.
- A serial from 2001 to 2007 whose digits 3 and 4 are above 12 does not fit the documented month rule. A 2001 recall of American units hints at a week number in that era but never says so, so the decoder reports such serials as not confirmed.
- Whirlpool and Kenmore: outside 8 April 2011 to 1 August 2016 the maker is not confirmed, so the rule is not applied. A. O. Smith's 2006 announcement names American Water Heater as the exclusive supplier of Whirlpool water heaters to Lowe's, but no source shows the serial format for those earlier years.
- Older serials with a letter in the middle, from before about 2000, are explained only by third parties and are not decoded.
Questions
Why choose a brand if the A. O. Smith format is the same?
For A. O. Smith, State, Reliance, American and U.S. Craftmaster the choice changes nothing. For Whirlpool and Kenmore it limits the rule to the period in which a recall confirms A. O. Smith as the maker, 8 April 2011 to 1 August 2016.
How do I turn the week number into a date?
Count from 1 January: week 15 starts in early April and week 37 in early September. A. O. Smith International places week 37 of 2020 at 7 to 13 September.
Is a Lochinvar water heater dated the same way?
No. Lochinvar has belonged to A. O. Smith since 2011 but keeps its own serial layouts, which have their own page here.
Related pages
- Lochinvar: Lochinvar belongs to A. O. Smith but keeps its own date codes.
- Rheem: Rheem also switched between month and week codes, in a different layout.
- Bradford White: Bradford White uses letters for the year and the month.
- All water heater brand families: Every brand family we decode, and the brands we do not decode yet with the reason.
- Where to find the data plate: Where the serial number sits on each type of equipment and how to copy it without mistakes.
- Service life estimates: What ENERGY STAR publishes about typical ages, and what kind of number each figure is.
Sources
Every rule on this page comes from the documents below, published by the manufacturer or a U.S. government agency. The date is when we last checked each one.
- FAQs (how to read the serial number) A. O. Smith Canada (hotwatercanada.ca). Checked .
- A. O. Smith recalls Ultra-Low NOx water heaters (CPSC recall 19-029, 8 November 2018) U.S. Consumer Product Safety Commission. Checked .
- Manufacturing date of the device A. O. Smith International. Checked .
- A. O. Smith recall of water heaters (CPSC recall 06-002, 6 October 2005) U.S. Consumer Product Safety Commission. Checked .