How to Read a Water Heater Serial Number (And Why It Matters)

Your water heater has a story stamped right onto it. The serial number. Most homeowners walk past it every day without realizing that a handful of letters and numbers can tell you how old your water heater is, whether it’s under warranty, and when it’s likely to fail.

Knowing how to read a water heater serial number can help you avoid surprise breakdowns, denied warranty claims, and costly emergency replacements.

Where to Find the Serial Number on a Water Heater

The serial number is typically located on the manufacturer’s rating plate , which is a sticker or metal tag attached to the side of the tank.

You’ll usually find it:

• On the upper half of the tank
• Near the gas control valve or electrical access panel
• On the side facing the room, not the wall

The label will include:

• Manufacturer name
• Model number
• Serial number
• Tank size
• Fuel type
• Voltage or BTU rating

The serial number is what tells us the age. The model number does not.

Why the Serial Number Is So Important

Reading the serial number allows a licensed plumber to determine:

• The manufacture date
• Whether the unit is still under manufacturer warranty
• If replacement parts are still available
• Whether the tank is near or past its expected service life

In Southern California, most standard tank water heaters last 8–12 years , depending on water quality, pressure, and maintenance. Many warranty claims are denied simply because the unit is older than the homeowner realized.

How Water Heater Serial Numbers Are Formatted

There is no universal serial number format. Each manufacturer uses its own system. Below are the most common water heater brands and how to read their serial numbers.

Rheem / Ruud Water Heaters

Rheem and Ruud use a straightforward format.

Example serial number: RH071234567

The first two numbers indicate the year

The next two numbers indicate the month

In this example:

07 = 2007

12 = December

Manufacture date: December 2007

Bradford White Water Heaters

Bradford White uses a letter-based code.

Example serial number: KD12345678

The first letter indicates the year

The second letter indicates the month

Bradford White year code example:

• A = 2004 or 2024
• B = 2005 or 2025
• C = 2006 or 2026
• D = 2007 or 2027
• E = 2008 or 2028
• F = 2009 or 2029
• G = 2010 or 2030
• H = 2011 or 2031
• J = 2012 or 2032
• K = 2013 or 2033
• L = 2014 or 2034
• M = 2015 or 2035
• N = 2016 or 2036
• P = 2017 or 2037
• S = 2018 or 2038
• T = 2019 or 2039
• W = 2020 or 2040
• X = 2021 or 2041
• Y = 2022 or 2042
• Z = 2023 or 2043

Month code:

• A = January
• B = February
• C = March
• D = April
• E = May
• F = June
• G = July
• H = August
• J = September
• K = October
• L = November
• M = December

In the example above:

K = 2013

D = April

Manufacture date: April 2013

AO Smith / State / American Water Heater

AO Smith family brands usually use this format:

Example serial number: 1805123456

The first two digits = year

The next two digits = week of the year

In this example:

18 = 2018

05 = 5th week of the year

Manufacture date: Early February 2018

GE Water Heaters

Most GE water heaters follow the same format as Rheem (since many were manufactured by Rheem).

First two digits = year

Next two digits = month

Always verify the manufacturer listed on the label to confirm the format.

Why Age Matters for Warranty Coverage

Most tank water heaters carry a 6-year, 9-year, or 12-year warranty, and that warranty starts on the manufacture date, unless you keep the installation documentation.

This is why reading the serial number correctly is critical before:

• Filing a warranty claim
• Repairing a leaking tank
• Investing in major repairs

If the tank itself is leaking and the unit is outside warranty, replacement is the only correct solution.

When to Call a Professional

If:

• The serial number is unreadable
• The brand uses an uncommon coding system
• You suspect the water heater is original to the home
• You’re unsure whether repair or replacement makes more sense
• A licensed plumber can confirm the age, inspect the installation, and help you plan before a failure occurs.

Pro Tip

If your water heater is 10 years old or older, start budgeting for replacement even if it’s still working. Tanks rarely give warning before they fail.

Need Help Identifying Your Water Heater’s Age?



At Rodgers Air Conditioning & Plumbing, we help homeowners throughout Southern California identify water heater age, assess remaining life, and plan code-compliant replacements before emergencies happen. Reach out and speak to a licensed technician today!

Knowing your serial number today can save you from a flooded garage tomorrow.