How Old Is My Water Heater? Read the Serial Number

By Ray Bennett · Updated 2 October 2026 · 5 min read · Checked against the sources at the end

How Old Is My Water Heater? Read the Serial Number

Short answer

The date is in the serial number, on the rating label on the side of the tank. Bradford White uses two letters, the year then the month. Rheem's first four digits are the month then the year. A.O. Smith's are the year then the week. A.O. Smith says a tank heater lasts 8 to 12 years and a tankless one 15 to 20.

How old is my water heater? The tank answers that itself. The date it was made is built into the serial number on its rating label, the sticker on the side that also carries the model number.

Each maker writes the date its own way, so the same four digits can mean two different dates. This page reads the serial numbers the way Bradford White, Rheem and A.O. Smith explain them in their own documents, then turns the age into a decision.

Before you start

What to carry: a torch and your phone, to photograph the label. Five minutes.

Gas or electric? Either. Gas and electric tanks carry the same kind of rating label, and the serial number is read the same way on both.

Photograph the whole label. The model number, the serial number and the size in gallons are all on it. A technician, a parts counter and a warranty check will all ask for them.

Three things that trip people up. The same digits, read two ways. Rheem puts the month first and A.O. Smith puts the year first. A serial starting 0917 would be September 2017 on a Rheem, and week 17 of 2009 on an A.O. Smith. Read it by the maker’s name on the label.

The same letter, twenty years apart. Bradford White’s year letters repeat every 20 years, so the letter alone never settles the decade. The count of digits after it does, as shown below.

The warranty clock. A.O. Smith says its warranty starts at installation, and that without proof of installation it starts from the date of manufacture. Keep the installer’s invoice with the manual.

Find the serial number

Check 1Free, five minutes

Find the label

On a tank. Look on the side of the tank for the rating label with the model and serial numbers on it. Rheem says the serial number on every one of its water heating rating labels has ten characters.

On a tankless heater. A.O. Smith says to check a tankless unit’s age from the serial number on the unit or in the manual.

Keep the numbers. Rheem’s online warranty check asks for the serial number. A.O. Smith checks warranty status online or through its technical support, and a part under warranty needs the model and serial numbers too.

Reading it, maker by maker

Where each maker puts the date. The Rheem and A.O. Smith serials are the makers' own examples. The Bradford White one is made up to show the pattern.

Check 2

Read the first few characters

Bradford White: two letters. Bradford White says the first two characters are the year and the month of manufacture. Everything after them is a production number.

Rheem: month, then year. Rheem’s serial has ten characters: two digits for the month, two for the year, a letter for the plant line, then a five digit serial. Its own example, 1209D01234, was made in December 2009.

A.O. Smith: year, then week. A.O. Smith’s guide for its service providers says the first two digits are the year and the next two are the week, and that a year can have up to 53 weeks. Its example starts 1719, the nineteenth week of 2017.

Any other brand. Look for a date printed on the label itself before you try to decode anything, and ask the maker if there is none. The three above are the ones their makers explain in writing.

Bradford White’s letters

Bradford White's production number grew from seven digits to eight in December 2007. That tells the two decades apart.

Check 3

Decode the two letters

The year letter. Bradford White’s chart starts at A for 1984 and runs through the alphabet, skipping I, O, Q, R, U and V, so there are 20 letters. At 2004 it starts again at A, and again at 2024, which makes B 2025 and C 2026.

The month letter. A is January and M is December, with I skipped. So J is September, K October and L November.

Which decade. Bradford White says the production number after the two letters was seven digits long before December 2007 and eight digits long after it. Count them.

One odd pair. Bradford White says a computer error put OA on some serials, and that those heaters were built in January 1997.

Letter	Year	Letter	Year
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

What the age tells you

Check 4Free to a new heater

Weigh the age against the fault

How long they last. A.O. Smith says a tank water heater typically lasts 8 to 12 years, and a tankless one 15 to 20 years with proper care. It puts the difference down to the sediment and corrosion a storage tank has to live with.

A young tank with a fault. Many faults are a part, not the tank: a water heater with no hot water, or the pilot on a gas one: a pilot that will not stay lit.

An older tank that leaks. Find where the water comes from first. A valve or a fitting is a repair, and a leak from the tank itself is not: finding a water heater leak.

Buying time. A.O. Smith says sediment and corrosion are what shorten a tank’s life. The anode rod is the part that corrodes instead of the tank: checking the anode rod and sediment in the tank.

Questions people ask

How can I tell how old my water heater is?

Read the serial number on the rating label on the side of the tank. Bradford White puts the year and month in the first two letters, Rheem the month and year in the first four digits, and A.O. Smith the year and week.

How old is my Bradford White water heater?

The first letter is the year and the second the month. The letters repeat every 20 years, so count the digits after them: seven means before December 2007, eight means December 2007 or later.

How do I read a Rheem serial number?

The first two digits are the month and the next two the year. Rheem’s example, 1209D01234, was made in December 2009.

How do I read an A.O. Smith serial number?

The first two digits are the year and the next two the week. A.O. Smith’s example starts 1719, the nineteenth week of 2017.

How long does a water heater last?

A.O. Smith says a tank water heater typically lasts 8 to 12 years, and a tankless one 15 to 20 years with proper care.

Is my water heater still under warranty?

Rheem and A.O. Smith both check it from the serial number. A.O. Smith says the warranty starts at installation, or at the date of manufacture if there is no proof of installation.

Sources: Bradford White's serial number date code chart and its FAQ "How to read the serial number date code reference chart?", Rheem's "How to locate and read your Rheem water heating serial numbers", A.O. Smith's July 2024 Service and Warranty Guide, and A.O. Smith's "How Long Do Tankless Water Heaters Last?"