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A.O. Smith Water Heater Age by Serial Number — Free Lookup

A.O. Smith

Also works for A.O. Smith-built labels: State, Reliance, American, Whirlpool, U.S. Craftmaster, Kenmore, GSW and John Wood.

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)
  • B and 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.

Frequently asked questions

Where is the serial number on an A.O. Smith water heater?
On the rating plate — a sticker on the side of the tank, usually in the upper half. It lists the model number and serial number together. On A.O. Smith tankless and heat pump models, the plate may be on the side panel or inside the front cover.
How do I read an A.O. Smith serial number?
The first two digits are the year and the next two are the week of manufacture. For example, serial 1914B000123 means week 14 of 2019 — early April 2019. Letters may appear before or inside the serial as factory codes; the date is read from the leading digits.
Do State, Reliance, and American water heaters use the same format?
Yes. State, Reliance, American, and several other brands are made by A.O. Smith and use the same year-then-week serial coding, so the same decoder works for all of them.
The first two digits of my serial are a letter and a number. What does that mean?
Some older A.O. Smith serials start with one or two letters as factory or line codes. If the leading characters are letters, skip them and read the first four digits as year and week — for example, AF04A093001 decodes to week 4 of 2004 (the A after 04 is a factory suffix).
How long does an A.O. Smith water heater last?
Most tank-style units last about 8–12 years. Regular maintenance — especially flushing sediment and replacing the anode rod — can push a unit toward the longer end of that range.
What is the warranty on an A.O. Smith water heater?
A.O. Smith tank warranties typically run 6–12 years depending on the model and line, counted from the manufacture date rather than the install date — so the serial number is the ground truth for coverage. Registration is required for the full term on some models; see the warranty guide on this site for the per-line details.