Water heater age from the serial number
To find out how old a water heater is, read the serial number on the rating label of the tank (or, on a tankless unit, of the cabinet). With most brands the first characters are a date code, but every manufacturer writes it differently: Bradford White and older Lochinvar tanks use two letters for the year and the month, Rheem uses digits for the month and the year, and the A. O. Smith brands count the year and the week. Pick the family that made your heater below.
The brand on the label is enough to choose: State, Reliance, American, U.S. Craftmaster, and Whirlpool and Kenmore from 2011 to 2016, are dated with the A. O. Smith rule; Ruud and Richmond, both built by Rheem, with Rheem's rule.
- Bradford White
Brands: Bradford White
Read the year and month letters at the start of a Bradford White serial number, with the 20-year letter cycle, the December 2007 length change and examples.
- Rheem
Brands: Rheem, Ruud (Rheem-built), Richmond (Rheem-built)
Find the manufacture date in a Rheem, Ruud or Richmond water heater serial number: the month-year and week-year layouts Rheem documents, with worked examples.
- A. O. Smith family
Brands: A. O. Smith, State, Reliance, American, U.S. Craftmaster, Whirlpool (2011-2016), Kenmore (2011-2016)
Decode A. O. Smith, State, Reliance, American and U.S. Craftmaster water heater serials: year and week, the 2008 switch, and Whirlpool and Kenmore units.
- Lochinvar
Brands: Lochinvar (residential tanks)
Read the build date in a Lochinvar residential water heater serial: the 1979-2011 letter code, the 2011 year-week layout, worked examples and caveats.
How water heater date codes differ
Letter codes are compact but can repeat: Bradford White and Lochinvar both reuse their twenty year letters every twenty years, so a letter can stand for two decades. Digit codes avoid the repeat but leave the century unprinted, which matters only for the oldest units. Week-based codes, used by A. O. Smith on units built after 2008 and by some Rheem electric tanks, date a heater to the week, while month codes give the month.
The date of manufacture is not the installation date. A heater can sit in a warehouse or a store before it reaches your house, so a few months between the two is normal.
Water heater brands we do not decode yet
- GE: GE tank manuals from 2003 to 2007 name Rheem as the maker under a trademark license, but neither GE nor Rheem explains GE serial numbers. Newer GE heaters are not documented.
- Navien: A U.S. recall documents where the date sits for three models from 2018 only; for other models the position is known only from third parties.
- Rinnai: Rinnai documents its serial layout in a service manual, but we have not added a Rinnai decoder to the site yet.
- Whirlpool and Kenmore outside 2011 to 2016: A. O. Smith is confirmed as the maker only for that window, so other years are not decoded.
These are left out on purpose: a date read with a borrowed or unconfirmed rule could be wrong by years. How we choose sources is explained on the methodology page, and typical service lives are on the service life page.
Page updated . Decoding rules last checked against their sources on the date shown with each source.