Water heater guide

How old is my water heater? How to read the serial number

Age is the first thing a plumber asks about, because it decides whether a repair is worth it. You can usually find it in two minutes from the label on the side of the tank.

Updated October 26, 2026 · 5 min read · By the Heater Doctor team

Plumber's tool bag, pipe wrenches and copper fittings beside a water heater

Short answer

Look at the rating label on the side of the tank for the serial number. Most brands code the manufacture date into its first few characters. On a Rheem water heater, the first two digits are the month and the next two are the year, so 0919 means September 2019. On a Bradford White, the first letter is the year and the second is the month. For other brands, the maker's warranty lookup tells you.

Find the label

The rating label is a sticker on the side of the tank, usually near the top on electric heaters and above the gas control on gas heaters. It lists the model number, the serial number, the capacity and the energy input. If it's hard to read, take a photo with the flash on and zoom in. A plumber can read the photo for you too.

Rheem, Ruud and Richmond

Rheem says the serial number on its water heating rating labels has ten characters. In its example, 1209D01234, the first two digits (12) are the month, the next two (09) are the year, then a plant code and a sequential number. So a heater whose serial starts 0919 was made in September 2019.

Bradford White

Bradford White says the first two characters of the serial number are the year and month of manufacture, and the rest is a production number. The year letters repeat on a 20-year cycle, and the year column never uses I, O, Q, R, U or V. From its chart:

Year: W = 2000 or 2020, X = 2001 or 2021, Y = 2002 or 2022, Z = 2003 or 2023, A = 2004 or 2024, B = 2005 or 2025, C = 2006, D = 2007, and so on.
Month: A = January, B = February, C = March, and so on to M = December. The letter I is skipped.

So a serial starting WC is March of 2000 or 2020. A heater that looks new is almost certainly the later date. Bradford White also notes that the production number grew from seven digits to eight in December 2007.

A. O. Smith, State and other brands

Date codes differ by brand and have changed over the years. The reliable way is the maker's own lookup. A. O. Smith's warranty verification page takes the serial number and returns the warranty details for the heater. Rheem and Bradford White run similar tools. If the house came with the heater, the build year gives a rough backstop.

What the age tells you

InterNACHI puts conventional tank heaters at roughly 6 to 12 years, with about 10 years typical. Our water heater lifespan guide goes deeper. As a rule of thumb, a heater under its warranty term is worth repairing, and a leaking tank past 10 years is usually time to replace.

Newer neighborhoods hit this all at once. The median home in Mead, Colorado was built in 2006, so many original heaters there are about 20 years old (see our Mead page). In Timnath, the median home dates from 2016, and many heaters may still be under warranty (see our Timnath page).