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American 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.

How Old Is Your American Water Heater?

American-branded water heaters are built by American Water Heater Company, an A.O. Smith subsidiary since 2006 — so they carry the same serial number format as A.O. Smith's own tanks, with the manufacture date in the first digits. Type the serial into the free decoder above for an instant answer, or read on to decode it by hand.

The same coding covers A.O. Smith's sister brands — State, Reliance, U.S. Craftmaster, GSW, and John Wood — plus older Whirlpool tanks built by American Water Heater Company.

Where to Find the Serial Number

Look at the rating plate (data plate) on the side of the tank — a silver or white sticker, usually in the upper half of gas and electric models, with the serial number printed beside the model number. On tankless and hybrid heat pump units, the plate is often on a side panel or behind the front cover.

Older stickers fade or get painted over — photograph the plate and raise the contrast; you only need the first four digits.

How the American Serial Format Works

The date code is year, then week, in the first four digits:

Worked example — 1908A002143:

  • 19 = 2019 (year)
  • 08 = week 8 (late February)
  • A and the remaining digits = factory and production sequence
  • Result: manufactured in week 8 of 2019

Watch for letter prefixes. Letters before or inside the date block are factory or product-line codes, not part of the date. Skip leading letters and read the first four digits you find — for example, CD144501287 decodes to week 45 of 2014.

Very old units. Some pre-2008 serials open with a month letter instead (A=January through M=December, skipping the letter I), followed by a two-digit year — so K06… means October 2006. The decoder above recognizes both styles.

Since the year is only two digits, 1445... could in theory be 2004 or 2014. Weigh the unit's condition and model number — and when in doubt, our decoder flags ambiguous cases rather than guessing.

Why Your American Water Heater's Age Matters

  • Lifespan. Tank water heaters average 8–12 years. Beyond that, internal corrosion makes tank failure — and a flooded floor — far more likely.
  • Warranty. American 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.
  • Maintenance timing. Sediment flushing and anode rod replacement pay off most mid-life; the exact age helps you schedule them in time.
  • Replacement planning. A tank past 10 years is living on borrowed time — knowing the date lets you shop calmly instead of during an emergency.

Sources

Brand ownership confirmed by A.O. Smith's corporate history (2006 acquisition of American Water Heater Company) and the A.O. Smith subsidiary list filed with the SEC. Product lineup from the official American Water Heaters site. Serial format verified against the InterNACHI water heater dating chart and A.O. Smith's production-date guidance.

Frequently asked questions

Who makes American water heaters?
American water heaters are made by American Water Heater Company, a wholly owned subsidiary of A.O. Smith since 2006. Its tanks are built in A.O. Smith factories alongside State, Reliance, U.S. Craftmaster, and GSW models, and share the same serial number date coding.
How do I read the date on an American water heater serial number?
Read the first four digits: the first two are the year and the next two are the production week. Serial 1908A002143 means week 8 of 2019 — late February 2019. Letters in the serial are factory or production-line codes, not part of the date.
Where is the serial number on an American water heater?
On the rating plate — a sticker on the upper half of the tank that lists the model and serial numbers side by side. On American tankless and hybrid heat pump units, the plate may be on a side panel or behind the front cover.
My American water heater is older and the serial starts with a letter. What then?
Most letter prefixes are factory codes — skip them and read the first four digits as year and week. Very old, pre-2008 units can instead open with a month letter (A=January through M=December, skipping I), so K06… would mean October 2006. Our decoder recognizes both styles.
How long should an American water heater last?
Tank models average 8 to 12 years of service. American tank warranties typically run 6 to 12 years depending on the model, counted from the manufacture date, so decoding the serial tells you whether a failing unit might still be covered.