How do I find the age of my water heater from the serial number?

Find the rating plate on the side of the tank, note the brand and serial number, then match the brand in the chart above. Most manufacturers encode the date in the first few characters — either digits (year + week or month + year) or, for Bradford White, two letters (year + month). Each brand links to a free decoder that does the reading for you.

Which water heater brands share the same serial number format?

Rheem, Ruud, and Richmond all come from Rheem Manufacturing and share one format (month + year after any letter prefix). A.O. Smith, State, Reliance, American, and U.S. Craftmaster come from A.O. Smith and share the year + week format. Kenmore was never a manufacturer — most units are A.O. Smith-built, with some Rheem and Whirlpool lines mixed in.

Why does my Bradford White serial decode to two different years?

Bradford White year letters repeat on a 20-year cycle, so the letter A means 1984, 2004, or 2024. No character in the serial separates the cycles, so the honest answer is a short list of possible years — use the unit’s condition, the ANSI revision year on the rating plate, and the age of the house to pick the right one.

What if my serial number does not match any format in the chart?

First check the rating plate itself — many Rheem-built units print the manufacture date in plain text, which overrides the serial. Then look for letter prefixes or faded characters and re-read the first few digits. If it still does not fit, the unit may be an uncommon brand or a very old format; the Building Intelligence Center and InterNACHI charts in the Sources below cover dozens more brands.

How long does a water heater last?

Most tank-style gas and electric water heaters last about 8–12 years, regardless of brand. Water quality, sediment flushing, and anode rod maintenance matter more than the badge on the tank — but once you know the exact age from this chart, you can plan a replacement before a failure floods your floor.

Water Heater Age Chart: Every Serial Number Format by Brand

Water Heater Age Chart by Serial Number

Every major water heater brand hides its manufacture date in the serial number on the rating plate — but each brand hides it differently. This chart lines up every format this site decodes, so you can identify the pattern at a glance, then jump to the free decoder for that brand. The formats below come straight from our decoder code, so the chart stays honest as the decoders are maintained.

Brand	Manufacturer	Serial format	Example	Decoder
Rheem	Rheem Manufacturing	Letter prefix, then MMYY (month + year); older units use WWYY (week + year); tankless often `MM.YY-xxxxx`	`R 0819 B10488` → August 2019	Rheem lookup
Ruud	Rheem Manufacturing	Same as Rheem — shared factories and date codes	`RU 0904B21710` → September 2004	Ruud lookup
Richmond	Rheem Manufacturing	Same as Rheem	`A141511869` → week 14 of 2015	Richmond lookup
A.O. Smith	A.O. Smith	YYWW in the first four digits (year + week); pre-2008 units may open with a month letter	`1914B000123` → week 14 of 2019	A.O. Smith lookup
State	A.O. Smith	Same as A.O. Smith since the 2001 acquisition	`1604J004619` → week 4 of 2016	State lookup
Reliance	A.O. Smith	Same as A.O. Smith	`1811A002456` → week 11 of 2018	Reliance lookup
Kenmore	Rebadged — mostly A.O. Smith, some Rheem or Whirlpool	Varies by supplier; most are A.O. Smith-style with the year in the 2nd and 3rd digits	`A03307353` → 2003 (A.O. Smith style)	Kenmore lookup
Bradford White	Bradford White	Two letters: 1st = year (20-year cycle), 2nd = month (A–M, skip I)	`FG1234567` → July 1989 or July 2009	Bradford White lookup

Retail Brand Labels: Same Format, Different Badge

The brands above are the manufacturers; the labels below are the names people actually see on their data plates. Every label shares the format of its manufacturer — decode it exactly the same way, and each label has its own free lookup page:

Label	Built by	Serial format	Lookup
Ruud	Rheem	MMYY after prefix	Ruud lookup
Richmond	Rheem	MMYY after prefix	Richmond lookup
GE	Rheem	MMYY after prefix	GE lookup
Hotpoint	Rheem	MMYY after prefix	Hotpoint lookup
Vanguard	Rheem	MMYY after prefix	Vanguard lookup
WeatherKing	Rheem	MMYY after prefix	WeatherKing lookup
Intertherm	Rheem	MMYY after prefix	Intertherm lookup
Montgomery Ward	Rheem	MMYY after prefix	Montgomery Ward lookup
Cimarron	Rheem	MMYY after prefix	Cimarron lookup
Everkleen	Rheem (Richmond sub-label)	MMYY after prefix	Everkleen lookup
Miller	Rheem	MMYY after prefix	Miller lookup
Mainstream	Rheem	MMYY after prefix	Mainstream lookup
Aqua Therm	Rheem	MMYY after prefix	Aqua Therm lookup
Coast to Coast	Rheem	MMYY after prefix	Coast to Coast lookup
Energy Master	Rheem	MMYY after prefix	Energy Master lookup
Rheem Professional	Rheem	MMYY after prefix	Professional lookup
State (incl. State Select)	A.O. Smith	YYWW	State lookup
Reliance	A.O. Smith	YYWW	Reliance lookup
American	A.O. Smith	YYWW	American lookup
U.S. Craftmaster	A.O. Smith	YYWW	Craftmaster lookup
Kenmore (most eras)	A.O. Smith, some Rheem	Varies by supplier	Kenmore lookup
Whirlpool	A.O. Smith (via American)	YYWW	Whirlpool lookup
Maytag	A.O. Smith	YYWW	Maytag lookup
Apollo	A.O. Smith	YYWW	Apollo lookup
Envirotemp	A.O. Smith	YYWW	Envirotemp lookup
GSW	A.O. Smith (Canada)	YYWW	GSW lookup
John Wood	A.O. Smith (Canada)	YYWW	John Wood lookup
Prestige	A.O. Smith	YYWW	Prestige lookup
Quaker	A.O. Smith	YYWW	Quaker lookup
Revere	A.O. Smith	YYWW	Revere lookup
True Value	A.O. Smith	YYWW	True Value lookup
Navien	Navien (tankless)	Digits + letter month code	Navien lookup
Rinnai	Rinnai (tankless)	Letter-letter (2009+) or YYMM digits	Rinnai lookup
Bosch	Bosch (tankless)	3-digit code or digits 5–7 (2010+)	Bosch lookup

If the name on your data plate isn't in either table, it's probably a private label from the same two factories — try the manufacturer page whose format the serial looks like (digits-first = A.O. Smith year+week or Rheem month+year; two leading letters = Bradford White).

Bradford White Year-Letter Chart

Bradford White is the outlier in the table above, so it earns its own chart. The first letter of the serial is the year on a 20-year repeating cycle (skipping I, O, Q, R, U, and V), and the second letter is the month, A through M skipping I — so A = January … M = December.

Letter	Years	Letter	Years
A	1984 / 2004 / 2024	L	1994 / 2014
B	1985 / 2005 / 2025	M	1995 / 2015
C	1986 / 2006 / 2026	N	1996 / 2016
D	1987 / 2007	P	1997 / 2017
E	1988 / 2008	S	1998 / 2018
F	1989 / 2009	T	1999 / 2019
G	1990 / 2010	W	2000 / 2020
H	1991 / 2011	X	2001 / 2021
J	1992 / 2012	Y	2002 / 2022
K	1993 / 2013	Z	2003 / 2023

Because the cycle repeats, F can mean 1989 or 2009 (and the cycle keeps extending in both directions). To pick the right year, weigh the unit's condition, the ANSI standard revision year printed on the rating plate, and the age of the house — a water heater can't be older than the building it serves. Our Bradford White decoder lists every plausible year rather than guessing.

How to Use This Chart

Find the rating plate. It's a silver or white sticker on the side of the tank, usually in the upper half. On tankless units, check the side panel or behind the front cover.
Check for a printed date first. Many newer Rheem-built plates show "MFG. DATE" in plain text — that always beats decoding.
Match the serial to a row above. If the first four characters are digits, think A.O. Smith family (year + week) or Rheem family (month + year). Two leading letters means Bradford White.
Open the brand's decoder. It validates the format, flags impossible characters, and handles the ambiguous cases — like Bradford White's repeating years or A.O. Smith's two-digit years.

One caution that applies to every brand: a two-digit year can point to more than one decade. 0414... on an A.O. Smith-built unit could be 2004 or 2014. When the difference matters — warranty claims, home sales — corroborate with the model number and the unit's apparent condition.

Why the Age Matters

Tank water heaters average 8–12 years of service. Past that window, internal corrosion makes tank failure — and a flooded floor — much more likely. Knowing the exact manufacture date tells you whether a warranty claim is still possible (most tank warranties run 6–12 years from the manufacture date, not the install date), and lets you schedule a replacement calmly instead of paying emergency rates after a leak.

Sources

Serial formats on this page are compiled from our own decoder implementations, each verified against manufacturer and industry references: the InterNACHI water heater dating chart, Bradford White's official serial-number guidance, Rheem's guide to reading serial numbers, A.O. Smith's production-date guidance, and the Building Intelligence Center water heater age guides.