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AO Smith Water Heater Age by Serial Number – Detailed Guide

Fact checked by Stephen Conklin

ao smith water heater age by serial number

Determining an AO Smith water heater age by serial number is one of the most practical and accurate ways of establishing the appliance’s warranty or replacement status.

A.O. Smith water heaters have four serial number styles, identifying model numbers from 1939 (if you can still get a fully-functioning unit) up to the present. Deciphering the unit identifier is essential to establish the water heater’s age.

The string of letters and numbers identifies an AO Smith water heater’s manufacture date and other relevant information. You can use the data to decide whether the water heater is under warranty or already nearing its expiration (requiring a replacement).

So, join us in analyzing and deciphering the alphanumeric code on your AO Smith water heater.

Table of Contents

AO Smith Water Heater Serial Number Structure and Location


The first order of business before you perform a serial number search is knowing where to look for the “code.” You cannot determine the AO Smith water heater age without the alphanumeric string.

AO Smith says you can check the water heater’s serial number on the appliance’s “rating plate.” You can see this “sticker” near the device’s bottom.

You can also check the original sales invoice or warranty document. Most dealers input the water heater’s technical information (i.e., model, series, and serial number) in these documents.

A.O. Smith’s serial number format underwent several changes through the years. The following are the alphanumeric styles in various AO Smith water heaters.

  • Format A1: YYWWA123456
  • Format A2: SYYWW F123456
  • Format A3: YYWW123456789
  • Format B: AMYYA123456
  • Format C: AMYY-1234567-S12
  • Format D: MYYA123456

These alphanumeric formats might seem confusing, but we must emphasize AO Smith no longer manufactures water heaters with serial numbers in Formats B to D.

Here’s a tip. If the AO Smith serial number only has three numbers in the alphanumeric string, you can bet the unit is “old.”

You now have a basic understanding of AO Smith water heater serial number styles, but how do you perform age identification?

Guide to Determining the Production Year of AO Smith Water Heaters

Learning how to read A.O. Smith’s serial number can be confusing at first. However, AO Smith recommends only checking the first four (or three) numbers in the water heater’s alphanumeric code. Here’s how to tell the age of the AO Smith water heater.

Format A1: YYWWA123456


This serial number format applies to newer AO Smith water heater models since 2010. The first two numbers (in red) identify the appliance’s manufacturing year. For instance, 13WWA123456 translates to a water heater produced in 2013.

The succeeding number pair identifies the water heater’s manufacturing week. We have 52 weeks in a year. Hence, we can expect the second string to number between 01 and 52. For example, YY24A123456 describes an AO Smith water heater produced on the 24th week (around mid-June).

Putting the two pieces of information together, we can say that AO Smith produced the water heater with serial number 1324A123456 between June 10 and June 16, 2013.

Format A2: SYYWW F123456


This AO Smith date code is nearly identical to the YYWWA123456 pattern, except it has a letter before the first four numbers and a space separating the last digit of the four-number code from the first letter of the following alphanumeric string.

You can disregard all other characters and focus only on the first four numbers in the series.

For instance, assume you have an AO Smith water heater with serial number S1802 F123456. We can interpret this as an appliance manufactured in the second week (the number pair 02) of 2018 (the number pair 18).

Format A3: YYWW123456789


This serial number style is similar to the A1 format, with the first four numbers identifying the AO Smith water heater’s manufacturing year and week.

However, the numbers don’t have a letter separating them from the second number series. Moreover, nine digits comprise the last set instead of just six.

For example, a water heater with the serial number 2204123456789 is an appliance manufactured in the fourth week of 2022.

You can use this information to check AO Smith warranty or learn more about your water heater. But what if the AO Smith water heater has a different serial number format?

Format B: AMYYA123456

Although AO Smith discontinued this serial number style, you might still see some units with this format (particularly old ones).

The AMYYA123456 format describes three crucial pieces of information. Although insignificant to buyers, the first letter denotes the factory that produced the water heater.

Only AO Smith knows the codes for its manufacturing facilities. The good news is AO Smith ditched the factory identifier in July 2004.

The second letter depicts the water heater’s manufacturing month. We can expect 12 letters from A to M. Note the 12th letter in the alphabet is “L.” However, AO Smith doesn’t use the letter “I” to avoid confusing consumers with the number “1.”

You can use the following age chart to understand AO Smith’s serial numbering system.

AO Smith’s Letter Code Corresponding Month
A January
B February
C March
D April
E May
F June
G July
H August
J September
K October
L November
M December

The first two numbers identify the water heater’s manufacturing year.

Let’s look at a serial number example: AF03A123456. This code suggests the AO Smith water heater was manufactured in June 2003. Unfortunately, we cannot zero in on the manufacturing date (unlike Formats A1 to A3, where we can limit the manufacturing timestamp to seven days).

Unsurprisingly, AO Smith ditched this system for a better one.

Format C: AMYY-1234567-S12


Reading eleven letters and numbers can be challenging for some. Hence, AO Smith addressed Format B’s shortcomings by adding hyphens to separate code sections.

It retains Format B’s first four-character manufacturing identifier – the factory code, manufacturing month, and manufacturing year.

The serial number no longer has the letter after the first two numbers. Instead, AO Smith moved the letter (with two numbers) to the end of the alphanumeric string.

Hence, we have a 14-character series grouped into three sections, with a hyphen separating the first and second sections and the second and third sections.

You only need to focus on the first section, the “AMYY.” Suppose the water heater has a serial number AC01-1234567-S12. In that case, AO Smith manufactured the water heater in March 2001.

Format D: MYYA123456

We mentioned that AO Smith ditched the factory identifier in July 2004. The result gave us the MYYA123456 format. It’s nearly identical to Format B, except it doesn’t have the letter before the manufacturing month identifier.

Hence, this water heater serial number only has three characters identifying its manufacturing date.

And that’s how you perform a serial number lookup on AO Smith water heaters, regardless of model and type.


Modern homeowners find determining an AO Smith water heater age by serial number straightforward. Although the water heater-related technical information can test the eyes because of its small print, knowing the appliance’s serial number offers many benefits.

You’ll know if the water heater is still under warranty and avail of AO Smith’s limited guarantees. Homeowners will also know when to start saving for a new water heater since these appliances don’t last a lifetime. Moreover, you’ll know if your water heater is subject to a recall procedure.

So, give this a try on your AO Smith water heater.

Read more: Guide to determine Whirlpool water heater age.

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