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Free tool

Water Heater Age Decoder

Type the serial number from the rating plate and get the month and year the heater was built, plus what that age means for a repair-or-replace decision.

Type it exactly as printed, including letters. Spaces do not matter.

Enter a serial number to see the manufacture date.

Rules from manufacturer documentation and inspector references listed under Sources. If the result looks wrong, the plate may use an older or regional format. Check the model number sticker for a printed date.

Where to find the serial number

The rating plate is a metal or foil sticker on the side of the tank, usually near the top on gas units and near the control panel on electric units. It lists the model number, serial number, capacity and energy ratings. The serial number is the one that encodes the date. The model number tells you the size and type but not the age, with one exception: Kenmore, where the model prefix tells you which factory built the heater.

How each brand codes the date

A.O. Smith, State, American Water Heater, Reliance, U.S. Craftmaster, Whirlpool. All built by A.O. Smith. The first two digits are the year, the next two are the production week. A serial starting with 1510 was built in week 10 of 2015, so early March. A serial starting with 2318 is week 18 of 2023, so early May.

Rheem, Ruud, Richmond, GE, Hotpoint. Built by Rheem. After an optional letter prefix (R, RN, RHLN and similar) the first two digits are the month and the next two the year. RHLN0722F12345 is July 2022. Some plates use a week code instead, so if the first pair is above 12, read it as the week of the year. The decoder handles both.

Watch the trap: 1219 on a Rheem plate is December 2019, but 1219 on an A.O. Smith plate is week 19 of 2012. Picking the right brand matters more than anything else here.

Bradford White. Two letters, then digits. The first letter is the year, the second the month. Bradford White skips I, O, Q, R, U and V in the year column, which leaves 20 letters that repeat every 20 years: A is 1984, 2004 and 2024; W is 2000 and 2020; Z is 2003 and 2023; B is 2025 and C is 2026. The month letter runs A (January) to M (December) without I. A plate starting WC was built in March 2020 or March 2000. The decoder shows the most recent possibility and names the earlier one so you can judge from the tank's condition.

Kenmore. Sears sold heaters from both factories. If the model number starts with 153, it is a Rheem and follows the Rheem month-year code. Other prefixes are A.O. Smith and follow the year-week code. Enter the model number in the decoder and it picks the right rule.

Brands not covered yet

Rinnai, Navien, Noritz, Bosch, Lochinvar, Giant and John Wood use their own formats, and the published references we checked disagree with each other on some of them. Rather than guess, we left them out. Most tankless units from these brands print the manufacture date in plain text on the rating plate. If you find the manufacturer's own documentation for one of these codes, tell us and we will add it with the source.

What the age means

Tank water heaters last 8 to 12 years on average. Tankless units last 15 to 20 years if they are descaled regularly. Past year 10, a tank that needs a repair costing more than a third of a replacement is usually not worth fixing, because the tank itself is next to go and a leaking tank causes water damage that costs more than the heater. The replacement cost calculator gives you the number to compare against.

Sources

  1. Bradford White For The Pro, Determining the Age of a Water Heater (official year and month letter tables)
  2. InspectApedia, Rheem Water Heater Age Decoder (serial formats and examples)
  3. Fast Water Heater Company, How Old Is My Water Heater? (A.O. Smith family week code, Rheem, Kenmore)
  4. Water Heater Hub, Water Heater Age Lookup (A.O. Smith and Bradford White examples)