A. O. Smith, State and American water heater age by serial number

Reviewed 2026-10-159 primary sourcesSee sources

A. O. Smith’s service guides say the first four digits of the serial number are the year and the week the water heater was built. A government recall notice confirms the same reading for A. O. Smith’s other brands.

Covers: A. O. Smith water heaters with all-number serials, and the State, American, Reliance and U.S. Craftmaster brands A. O. Smith also makes. Older letter-coded serials aren’t covered.

Where to find the serial number

• The serial number is on the rating plate. Newer plates also carry a QR code that shows the model, serial and warranty status when scanned.^[4]

Date formats A. O. Smith documents

Year + weekall-number serials; start date not stated

A. O. Smith doesn’t say when this layout began. Its example is a 2010s serial, so we read the first two digits as 20YY; a serial made before 2000 in another layout would be misread.^[1]

What A. O. Smith says

• Digits 1–2 are the year of manufacture and digits 3–4 the week, from 01 to 53. A. O. Smith doesn’t explain the remaining digits.^[1]
• A 2018 recall of ultra-low NOx gas water heaters sold as American, A. O. Smith, Kenmore, Reliance, State, U.S. Craftmaster and Whirlpool says the first four serial digits are the year and week of production, for units made from April 2011 to August 2016.^[3]
• A. O. Smith’s service guide lists the State, Reliance and American brand lines next to its serial guide and checks warranty for all of them in one system.^[2]
• A. O. Smith says most of its water heaters last about 8 to 12 years.^[8]

Worked examples

• 1719106145074: 17 is the year and 19 the week: built in week 19 of 2017. This is A. O. Smith’s own example.^[1]

What the serial can’t tell you

• The serial shows when the heater was made, not when it was installed. A. O. Smith starts the warranty at installation and uses the manufacture date only when there’s no proof of installation.^[1]
• Warranty length depends on the model and how it is used; it isn’t in the serial number.^[1]
• American Water Heater starts its residential warranty on the purchase date, and uses the manufacture date only without a bill of sale.^[7]
• A. O. Smith doesn’t say when the year-and-week layout started or how older serials are read.^[2]
• Serial formats used before the all-number layout (including older American and U.S. Craftmaster serials) aren’t explained by any source we could cite.
• Which calendar day week 01 starts on isn’t stated.

Recalls on record

The U.S. Consumer Product Safety Commission lists these recalls naming A. O. Smith equipment. Check the recall notice itself for the exact models and serial ranges.

• Certain 30 And 40 Gallon A.O. Smith LP And Natural Gas Water Heaters Voluntarily Recalled (1991-11-05, recall 92016)^[9]
• LP Polaris Comfort Systems Recall/Repair by American Water Heater (1996-09-25, recall 96191)^[9]
• CPSC, American Water Heater Co. Announce Recall to Replace Burners in Gas Water Heaters (2001-10-18, recall 02020)^[9]
• CPSC, A.O. Smith Announce Recall of Water Heaters (2005-10-06, recall 06002)^[9]
• A.O. Smith Recalls Gas Water Heaters Due to Fire and Carbon Monoxide Hazards (2008-04-03, recall 08241)^[9]
• A.O. Smith Recalls John Wood Brand Oil-Fired Water Heaters Due to Fire and Burn Hazards (2015-06-02, recall 15155)^[9]
• A. O. Smith Recalls Ultra-Low NOx Water Heaters Due to Fire Hazard (2018-11-08, recall 19029)^[9]
• A. O. Smith Recalls 30-Gallon Gas Water Heaters Due to Fire Hazard; Sold Exclusively at Lowe's (2018-11-08, recall 19030)^[9]

Ask A. O. Smith

• State warranty verification: Check coverage for a State water heater by serial number.^[5]
• American warranty verification: Check coverage for an American water heater by serial number.^[6]