A. O. Smith date code: year, then month or week
A. O. Smith says to read “the first four numbers, ignoring any letter that may start the serial number.” The first two numbers are the year. The next two are the month for heaters built before 2008, and the week for heaters built after 2008.
Manufacture date, not install date or warranty status. A date code tells you when the maker built the unit. It does not tell you when it was installed, whether any warranty applies, or what condition the unit is in.
A. O. Smith's rule
| Part of the serial | Built before 2008 | Built after 2008 |
|---|---|---|
| Leading letter, if any | Ignore | Ignore |
| Digits 1–2 | Year | Year |
| Digits 3–4 | Month | Week |
A. O. Smith's international site gives the same year-and-week layout. Its example serial starts with 20 and 37, which it reads as week 37 of 2020, “between September 7 and 13, 2020.”
Read your code
The 2008 gap
A. O. Smith's FAQ says “before 2008” and “after 2008” but does not say which rule applies to units built in 2008. For a code starting 08, our reader shows both the month and the week reading.
Which A. O. Smith sites we used
Both pages are A. O. Smith sites: hotwatercanada.ca is A. O. Smith's Canadian site, and aosmithinternational.com is its international site. We have not yet checked A. O. Smith's US site. If your heater carries a different serial format, these rules may not apply.
No affiliate links are live on this site. If we add any, we will mark them and explain them on our disclosure page. Links never change a size or a date rule.
Sources
- A. O. Smith Canada, FAQs: https://www.hotwatercanada.ca/faqs/, accessed 2026-10-27
- A. O. Smith International, Production date of my device: https://aosmithinternational.com/manufacturing-date-device/, accessed 2026-10-27