Find Your A.O. Smith Water Heater's Age
A.O. Smith encodes the manufacture date directly in the first digits of its serial numbers, so dating one of their water heaters is straightforward once you know the pattern. Enter your serial number in the free decoder above for an instant answer, or follow the guide below to read it yourself.
The same format applies to A.O. Smith's sister brands, including State, Reliance, American, and U.S. Craftmaster — all built in A.O. Smith factories with the same date coding.
Where to Find the Serial Number
Check the rating plate (data plate) on the side of the tank — a silver or white sticker, usually in the upper half of the unit on gas and electric tank models. The serial number is printed right next to the model number. On A.O. Smith tankless and hybrid heat pump units, the plate is often on the side panel or behind the front cover.
Serials on older units can fade or get painted over. If yours is hard to read, take a photo with your phone and bump the contrast — you only need the first four digits to get the date.
How the A.O. Smith Serial Format Works
The date code is year, then week, in the first four digits:
Worked example — 1914B000123:
19= 2019 (year)14= week 14 (early April)Band the remaining digits = factory and production sequence- Result: manufactured in week 14 of 2019
Watch for letter prefixes. Some serials start with letters, or insert a letter inside the date block — these are factory or product-line codes, not part of the date. Skip leading letters and read the first four digits you find. For example, AF04A093001 decodes to week 4 of 2004 (the A after 04 is a factory suffix), and 1604J004619 decodes to week 4 of 2016.
Because the year is only two digits, a serial like 0414... could in theory mean 2004 or 2014. Compare the unit's apparent condition and the model number — and when in doubt, our decoder flags ambiguous cases instead of guessing.
Why the Age of Your Water Heater Matters
- Lifespan. Tank water heaters average 8–12 years of service. Beyond that, internal corrosion makes tank failure — and a flooded floor — much more likely.
- Warranty. A.O. Smith tank warranties typically run 6 to 12 years depending on the model, counted from the manufacture date. Decoding the serial tells you whether a repair might still be covered before you spend money on it.
- Maintenance timing. Sediment flushing and anode rod replacement matter most in the middle years of a tank's life; knowing the exact age helps you schedule them while they still pay off.
- Replacement planning. A unit past 10 years is living on borrowed time. Knowing the date lets you shop for a replacement calmly instead of during an emergency.
Sources
Serial format details verified against the InterNACHI water heater dating chart, A.O. Smith's own production-date guidance, and the Fast Water Heater rating-plate guide.