How old is my Rheem water heater?

By Dana Whitlock. Updated October 2026. Official format.

Rheem changed its water heater serials in 2012, but the year never moved. It is always the second pair of the four date digits. Before 2012 the first pair is the month. From 2012 on it is the week, with a factory letter in front.

Rheem explains the layout on its own website and in a technical service bulletin for contractors, so this is an Official format and the decoder above follows the maker's documents. Newer Rheem labels go further and print the manufacture date in plain text, which beats any decoding.

Where to find the label on a Rheem water heater

Rheem puts the rating label on the front of tank-type heaters, usually in the upper half of the jacket. On labels printed since 2012, the third line shows the manufacture date outright, so check there first. If the label is in a tight closet, use a flashlight and read from where you stand. Everything you need is on the outside. Leave the burner door and electrical covers closed, especially on an electric tank with the power on.

How to read the code

Rheem's original layout is ten characters: two digits for the month, two for the year, a plant or line letter, then a five-digit count. Rheem's own example is 12 09 D 01234, built in December 2009. Many older tanks add a short letter prefix such as R, RH, RN or RHLN before the date digits; skip it. The layout introduced in 2012 is plant letter, two-digit week, two-digit year, five-digit count: M141209135 is week 14 of 2012 at the Mexicali plant. Plant letters are A for Montgomery, W for Water Heater Innovations, Q for Nuevo Laredo, M for Mexicali and C for Canada. A trailing letter after the count marks a factory conversion. It has nothing to do with the date.

Real serials in this code

When the format changed

Rheem did not flip every factory on the same day. The Mexicali plant moved to the new label on April 2, 2012, Nuevo Laredo followed on June 4, 2012, and the rest switched as they moved to a new ordering system, so 2012 and 2013 tanks can carry either layout. The tell is where the letter sits. A letter after the four date digits (as in 1209D01234 or RH0806B17262) means month then year. A single letter before the four digits, followed by exactly five digits, means week then year. Even if you mix the two up, the year comes out the same, because it is always the second pair. For a final check, the printed date on newer labels and Rheem's warranty lookup both settle it.

Who makes Rheem

Rheem traces its start to 1925 and builds water heaters under three main names: Rheem, Ruud and Richmond. All three print the same serial layouts, and Rheem's bulletin on reading serials covers Rheem and Ruud together. Ruud is named for Edwin Ruud, who invented the automatic gas water heater; Richmond is the brand Rheem has long used for retail sales. A Ruud or Richmond tank from the same plant and week will carry a serial you read exactly like a Rheem.

How sure is this?

Official format. Rheem publishes how its serial numbers encode the date. We tested the rheem rules against 17 serials, 13 of them with a date known from a recall notice, a printed label date or the maker. None decoded to a wrong year; codes whose year mark repeats show every possible reading. Always confirm with Rheem's serial lookup before you spend money on the answer.

Quick notes

• Read the printed manufacture date on the third line of post-2012 labels before decoding anything.
• Ignore letter prefixes like RH or RHLN at the start of an older serial; the date starts at the first digit.
• If a serial reads as month 23 or 41, you are looking at a week number, which means the 2012-and-later layout.
• Rheem's warranty lookup takes the serial and shows coverage, which also confirms the build date.