How to Tell the Age of Your AO Smith, State, or Rheem Water Heater

 

Wondering how old your water heater is?
Knowing the age of your unit is a smart move — it helps you plan for maintenance, avoid surprise breakdowns, and even improve efficiency. Whether you’ve got an AO Smith, State, or Rheem water heater, here’s a quick guide to figure out how old your tank is by reading the serial number.

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AO Smith & State Water Heaters

AO Smith and State are manufactured by the same company and use very similar serial number formats.

• Look for a sticker or metal plate on the side of the tank.

• Find the serial number — it typically starts with two letters followed by numbers.

• The first two numbers after the letters are the year of manufacture.

Example:
Serial # MJ18456789
The “18” tells you the unit was made in 2018.

So if you're seeing rusty water, strange noises, or just wondering if it's time for a replacement — now you know how old your system really is.

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Rheem Water Heaters

Rheem’s serial number format is a little different but just as simple.

• Look for the serial number (usually begins with a date code).

• The first four digits represent the month and year.

Example:
Serial #0519A12345
“05” = May, and “19” = 2019
So your Rheem water heater was built in May of 2019.

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Why This Matters

Most residential water heaters last 8–12 years. Once they get up in age, performance drops and the risk of failure increases. By knowing the age, you can plan ahead and even save money by replacing before an emergency strikes.

We recommend keeping an eye out for:

• Rusty or discolored water

• Water around the base of the unit

• Rumbling or popping noises

• Inconsistent hot water

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Need Help? We’re Here!

At Rooter Man SC, we help homeowners all over Charleston and the Lowcountry figure out the best plan for their water heaters — repair, maintenance, or replacement. Just send us a photo of your water heater’s label and we’ll do the detective work for you!

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