How to read an A.O. Smith serial number
Look at whether the serial starts with digits or with a letter. That tells you which style it is.
Starts with digits: year + week (about 2008 on)
The first two digits are the year and the next two are the week of the year [1][2]. Most of these serials are 11 characters: four digits, a letter and six digits. Some are all digits, and some carry an S in front, which you can skip.
12 10 A002243 → 2012, week 10 → around early March 2012
A week number gives the date to within a few days; the decoder shows the month that week falls in. Energy Trust of Oregon says this style has been used “since about 2008”, and the Building Intelligence Center says the old style ended between 2008 and 2010, so there is no exact switch-over date.
Starts with letters: month letter + year (before about 2008)
Find the two-digit year. The letter just before it is the month: A for January through M for December, with no I[1][3][4]. Many serials have one extra letter in front of the month, a factory code that the Building Intelligence Center says was dropped after July 2004.
A F 04 A093001 → factory A, F = June, 04 = 2004 → June 2004
The letter J
InterNACHI’s worked examples read month letter J as October, but its own rule (A = January … M = December), the Building Intelligence Center’s month table and an inspector’s chart all make J September[3][1][4]. We use September and say so in the result. Energy Trust writes the month range as “A through N”, but twelve letters skipping I end at M.
Worked examples
| Serial | Style | How it reads | Made | Example from |
|---|---|---|---|---|
1210A002243 | Year + week first (about 2008 on) | 12 = year ’12; 10 = week 10 of the year | Week 10 of 2012 (around March) | Building Intelligence Center |
S1318F000046 | Year + week first (about 2008 on) | 13 = year ’13; 18 = week 18 of the year | Week 18 of 2013 (around May) | Building Intelligence Center |
1836111786352 | Year + week first (about 2008 on) | 18 = year ’18; 36 = week 36 of the year | Week 36 of 2018 (around September) | Building Intelligence Center |
0805A123456 | Year + week first (about 2008 on) | 08 = year ’08; 05 = week 5 of the yearEnergy Trust example 0805AXXXXXX with the X digits filled in. | Week 5 of 2008 (around February) | Energy Trust of Oregon |
AF04A093001 | Month letter + two-digit year (before about 2008) | F = month letter (June); 04 = year ’04 | June 2004 | Building Intelligence Center |
E07A135491 | Month letter + two-digit year (before about 2008) | E = month letter (May); 07 = year ’07 | May 2007 | Building Intelligence Center |
AJ89123456 | Month letter + two-digit year (before about 2008) | J = month letter (September); 89 = year ’89InterNACHI captions "AJ89xxx" as October 1989, but its own rule (A = January … M = December) and Building Intelligence Center give J = September. | September 1989 | InterNACHI |
GG031495366S29 | Month letter + two-digit year (before about 2008) | G = month letter (July); 03 = year ’03Printed as GG03-1495366-S29; hyphens removed by normalization. | July 2003 | Building Intelligence Center |
Where to find the serial number
On the rating plate label on the tank jacket. On some installations it’s covered by an insulation blanket, so lift the blanket carefully to read it. Glascote, PermaGlas and National are A.O. Smith names that use the same codes.
What this page doesn’t decode
1970s serials written like “A20-H-78-015482”. Only one source describes them, so the decoder reports them as not recognised rather than guessing.
Common questions
How do I tell how old my A.O. Smith water heater is?
If the serial starts with four digits, the first two are the year and the next two the week. If it starts with a letter, find the two-digit year; the letter in front of it is the month.
What does a serial like 1836111786352 mean?
It’s the all-digit version of the newer style: 18 = 2018 and 36 = week 36, which is early September.
Is State the same as A.O. Smith?
State is an A.O. Smith brand and uses the same two styles. Its page has State’s own examples:State water heater age.
Not affiliated with A.O. Smith. The brand name is used only to say which serials this decoder reads.
Sources
- Building Intelligence Center: A.O. Smith Water Heater AgeUsed for: Year + week first (about 2008 on); Month letter + two-digit year (before about 2008).
- Energy Trust of Oregon: Serial Number Decoder: Water Heater (PDF)Used for: Year + week first (about 2008 on); Month letter + two-digit year (before about 2008).
- InterNACHI (International Association of Certified Home Inspectors): InterNACHI Water Heater Dating ChartUsed for: Month letter + two-digit year (before about 2008).
- Honest Home Inspections, LLC (hosted by InspectAPedia): How to determine Water Heater and Furnace Age (PDF, last updated 2009-01-06)Used for: Month letter + two-digit year (before about 2008).