# How old is my water heater? Reading the manufacture date from the serial number, brand by brand

> Rheem reads month then year (1209 = Dec 2009); A.O. Smith International and Lochinvar read year then week (2037 = week 37 of 2020); Bradford White uses letters.

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| Source | https://ownerspec.com/plumbing/guides/water-heater-age-serial-number-date-code/ |
| Publisher | OwnerSpec (https://ownerspec.com/) |
| Published | 2026-10-03 |
| Updated | 2026-10-03 |
| Facts verified | 2026-10-03 |
| Disclosure | Contains affiliate links. OwnerSpec may earn a commission at no cost to the reader. |

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## Short answer

The manufacture date of a water heater is encoded in the serial number on its rating label,
and the format depends on the brand. Rheem serials run 10 digits: the first two are
the month and the next two the year, so Rheem's own example 1209D01234 was built in December
2009. A. O. Smith International and Lochinvar reverse the order: the first two digits are the
year and the next two the week, so 2037 means week 37 of 2020 and Lochinvar's 1142N012345 means
the 42nd week of 2011. Bradford White uses two letters: the first is the year (A = 2004 or 2024, because the
letters repeat every 20 years) and the second the month, A for January through M for December,
skipping I. Once the date is known, A. O. Smith and Rheem both print a typical tank life of
8 to 12 years, and ENERGY STAR says a heater more than 10 years old is one to consider
replacing.

## Fact sheet

- **Answer:** The serial number on the rating label carries the manufacture date, read by brand: Rheem uses month then year (1209D01234 is December 2009), A.O. Smith International and Lochinvar use year then week (2037 is week 37 of 2020), and Bradford White uses a year letter then a month letter (A is 2004 or 2024). Rheem prints a tank life of 8 to 12 years.
- **Basis:** Each maker's own serial-number support page or warranty document: Rheem's serial number page, A. O. Smith International's production date page, the Lochinvar warranty-by-serial-number PDF for Lochinvar's own tanks, Bradford White's My Water Heater page and date code reference. Service life and replacement signs come from ENERGY STAR, A. O. Smith, Rheem and Bradford White as each prints them.
- **Assumptions:** A residential storage tank water heater sold in the United States. Tankless and heat pump units carry the same serial formats where the maker says so, but the service-life figures on this page are the makers' tank figures.; The brand on the label is the brand that built the tank. Whirlpool, Kenmore and GE labels are not decoded here because no maker page decoding their serials was readable for this page.; A serial number from a format older than the one each maker documents (Rheem before the 10-digit series, A. O. Smith before 2008) is not covered; those formats were not verified from maker pages.
- **Method:** A comparison of manufacturer serial-number support pages, warranty documents and replacement-advice pages, read on 3 October 2026. Every decode rule and example is copied from the maker's own document and attributed to it. No heaters were inspected for this page.
- **Primary source:** [Rheem: How to locate and read your Rheem water heating serial numbers](https://www.rheem.com/how-to-locate-and-read-your-rheem-water-heating-serial-numbers/) (manufacturer or vendor document)
- **Facts verified:** 2026-10-03
- **Last updated:** 2026-10-03
- **Canonical URL (cite this):** https://ownerspec.com/plumbing/guides/water-heater-age-serial-number-date-code/

If the floor around the base is already wet, skip the serial number and go to
[where the leak is coming from](/plumbing/guides/water-heater-leaking-where-from/): the date
only matters while the tank still holds water.

## How do you read the date from the serial number?

Find the brand on the rating label first. The same four digits mean December 2009 on a
Rheem and week 9 of 2012 on an A. O. Smith, because Rheem reads month then year and
A. O. Smith reads year then week. Every rule and example below is the maker's own.

| Brand | Serial format | Maker's example | How to read it | Maker's document |
|---|---|---|---|---|
| Rheem | 10 digits: MM YY P NNNNN | 1209D01234 | Positions 1-2 month, 3-4 year, 5 plant line letter, 6-10 consecutive number: December 2009, plant D | Rheem serial number page |
| A. O. Smith | YY WW then production digits | 2037 | First two digits year, next two week: 2020, week 37 (September 7-13, 2020) | A. O. Smith International production date page |
| Lochinvar (current) | 11 characters: YY WW P NNNNNN | 1142N012345 | First two characters year, next two week, fifth plant, last six production code: 42nd week of 2011 | Lochinvar warranty-by-serial PDF |
| Lochinvar (older two-letter series) | Letter year, letter month, then digits | KJ-1000130 | First letter year, second letter month: September 1993 | Lochinvar warranty-by-serial PDF |
| Bradford White | Letter year, letter month, then digits | DG6322957 | D = 2007, G = July: July 2007. Year letters repeat every 20 years | Bradford White My Water Heater page and date code reference |
| Whirlpool, Kenmore, GE | Not decoded here | | No maker page decoding these serials was readable for this page | None |

Rheem's lifespan article says the date "is often encoded in the unit's serial number" but
gives no decode steps; the rule in the table is from Rheem's dedicated serial number page.
A. O. Smith's rule comes from A. O. Smith International, the company's European site, which
documents its own models; no US A. O. Smith page decoding the serial was readable when this
page was written, so check a US tank's reading against its install records before relying on it.

## What do the Bradford White letters mean?

Bradford White is the one brand that uses no digits for the date, so it needs its own chart.
The maker's page says the first character is the year, the second the month, that the year
letters skip I, O, Q, R, U and V, and that the month letters run A to M skipping I.

| Year letter | Year | Month letter | Month |
|---|---|---|---|
| W | 2000 | A | January |
| X | 2001 | B | February |
| Y | 2002 | C | March |
| Z | 2003 | D | April |
| A | 2004 | E | May |
| B | 2005 | F | June |
| C | 2006 | G | July |
| D | 2007 | H | August |
| E | 2008 | J | September |
| F | 2009 | K | October |
| G | 2010 | L | November |
| H | 2011 | M | December |
| J | 2012 | | |
| K | 2013 | | |
| L | 2014 | | |
| M | 2015 | | |
| N | 2016 | | |
| P | 2017 | | |

The year column is Bradford White's printed date code reference, which stops at P for 2017.
The letters repeat on a 20-year cycle, and the maker's page gives the consequence in one
line: "A = 2004 or 2024". A tank with a worn label and an A is either 2 years old or 22,
and the look of the tank, not the letter, settles it. For a letter after P, ask Bradford
White with the full serial rather than extrapolating the cycle.

## How long do the makers say a water heater lasts?

There is no single industry figure, and the makers do not agree with each other. The table
prints each statement as published, without averaging them.

| Who | What the document says | Document |
|---|---|---|
| A. O. Smith | "the average life expectancy of a water heater is about 8 to 12 years" | When to repair or replace |
| Rheem | Tank water heaters "typically last 8-12 years"; tankless "can last 15-20+ years with proper care" | Water heater lifespan article |
| ENERGY STAR | "If you suspect your water heater is more than 10 years old, it is time to consider replacing it"; its heat pump savings math assumes a 13-year life | When should you replace your water heater |
| Bradford White | States no lifespan; "If your water heater is more than 10 years old, it makes sense to consider replacing it now, before you notice any problems" | Is your water heater too old |

On Lochinvar tanks the serial date also starts the warranty. Lochinvar's warranty
document says the residential tank warranty runs from 60 days after the date of manufacture
"as determined by the serial number", six years on current prefixes and five on older ones.
A tank installed a year after it was built has a year less of coverage than the installer
said.

## Which signs do the makers list for replacement?

Age alone is not a replacement sign in any maker's document: each pairs it with a symptom.
The symptoms below are the ones the three makers and ENERGY STAR print, with the page on
this site that confirms each.

| Sign | Who lists it | What to do, and where |
|---|---|---|
| Water around the base of the tank | A. O. Smith, Rheem, Bradford White | Find the source first: a valve, a fitting or the tank. See [where the leak is coming from](/plumbing/guides/water-heater-leaking-where-from/) |
| Leaks from joints, seals or seams, corrosion | ENERGY STAR | A fitting leak is a repair; a seam leak is the tank |
| Rust-colored or discolored hot water | A. O. Smith, Rheem, Bradford White, ENERGY STAR | Check the anode first on a tank under 10 years: [anode rod by model](/plumbing/parts/water-heater-anode-rod-by-model/) |
| Rumbling, popping or banging | A. O. Smith, Rheem, Bradford White, ENERGY STAR | Sediment: [popping noise and sediment flush](/plumbing/guides/water-heater-popping-noise-sediment-flush/) |
| Odor in the hot water | Bradford White | Bradford White lists it as a replacement sign; check the anode and the water supply before blaming the tank |
| Runs out of hot water sooner than it used to | ENERGY STAR (sediment reducing capacity), A. O. Smith | Flush first, then check the size against demand: [first hour rating calculator](/plumbing/calculators/water-heater-size-first-hour-rating/) |

**Before you buy a replacement**

Do not order a new heater from the date alone. A 9-year-old tank with rusty water may
only have a spent anode, and a magnesium anode rod
is a fraction of the price of the tank; the anode page lists the thread and length by model.
A 12-year-old tank that is dry and quiet is inside Rheem's and A. O. Smith's printed range
and outside nothing. What it should not be is on a bare floor: a
drain pan under it catches the base leak every
maker names as the end. The pan listing names electric heaters, so check the tank diameter
and your local code before putting one under a gas unit.

## What should you do first?

1. Photograph the rating label and read the brand before any digit: Rheem is month-year, A. O. Smith International and Lochinvar are year-week, Bradford White is letter-letter.
2. Decode the date with the table above and write the month and year on the tank in marker.
3. Under 10 years with rusty water or odor: check the anode by model, then flush.
4. Over 10 years and dry: fit a drain pan, keep flushing, and size the replacement now with the first hour rating calculator so the day it leaks is a swap, not a search.
5. Any water at the base: go to the leak page and find the source before deciding anything.

## The picks

- **Eastman 60286 Flexible Magnesium Anode Rod, 42 in, 3/4 in NPT**: A tank under 10 years old that still holds water: check the anode before deciding on replacement (Listing states a 42 inch flexible magnesium rod with a 3/4 x 3 in NPT stainless nipple; confirm your model's anode thread and length on the anode rod parts page before ordering) Amazon: https://www.amazon.com/dp/B09G3L9S17/?tag=ownerspec-20
- **Camco 11460 Plastic Water Heater Drain Pan with Fitting, 22 in**: A tank past 10 years that you are keeping for now: a pan under it catches the base leak the makers warn about (Listing states a 22 inch plastic pan with a drain fitting and names electric water heaters; check the tank diameter and any local code before use under a gas heater) Amazon: https://www.amazon.com/dp/B000PSD6X0/?tag=ownerspec-20

## Frequently asked questions

### Where is the serial number on a water heater?

On the rating label, the printed sticker with the model number, capacity and input rating. Rheem's FAQ puts it on the front of tank-type heaters and on the front or right side of its tankless units. A. O. Smith says the serial number is on the rating plate sticker.

### Why does the same four-digit code give two different dates?

Because the brands disagree on digit order. Rheem's own page reads the first two digits as the month and the next two as the year, so 1209 is December 2009. A. O. Smith International reads the first two as the year and the next two as the week, so 1209 would be week 9 of 2012. Identify the brand on the label before decoding anything.

### Does the manufacture date start the warranty, or the install date?

On Lochinvar tanks, the manufacture date. Lochinvar's warranty-by-serial-number document says the residential tank warranty is effective 60 days from the date of manufacture as determined by the serial number, with a six-year limited warranty on current prefixes and five years on older ones. A tank that sat in a warehouse for a year has already used part of its warranty before it is installed.

### How long does a water heater last according to the makers?

A. O. Smith prints an average life expectancy of about 8 to 12 years, and Rheem prints 8 to 12 years for tanks and 15 to 20 or more for tankless units with proper care. ENERGY STAR and Bradford White do not print a lifespan; both say a heater more than 10 years old is one to consider replacing, and ENERGY STAR's savings math assumes 13 years.

### What signs do the makers say mean replace rather than repair?

A. O. Smith lists leaks around the base of the tank, rust-colored or odd-smelling water, rumbling or popping, and a heater more than 10 years old. Rheem lists leaking from the base, rusty or discolored hot water and persistent rumbling from hardened sediment. ENERGY STAR adds corrosion and leaks from joints, seals or seams. A leak from the tank itself is the one that cannot be repaired.


## Sources

- [Rheem: How to locate and read your Rheem water heating serial numbers](https://www.rheem.com/how-to-locate-and-read-your-rheem-water-heating-serial-numbers/) (manufacturer or vendor document)
- [Rheem FAQs (location of the model and serial label)](https://www.rheem.com/faqs/) (manufacturer or vendor document)
- [A. O. Smith International: Production date of my device](https://aosmithinternational.com/manufacturing-date-device/) (manufacturer or vendor document)
- [Lochinvar: Warranty information by serial number, Rev 20 (PDF)](https://assets.lochinvar.com/damroot/Original/10013/061449WARR_Rev%2020_100161789_2000019081.pdf) (manufacturer or vendor document)
- [Bradford White: My Water Heater (serial number date code)](https://www.bradfordwhite.com/my-water-heater/) (manufacturer or vendor document)
- [Bradford White: Serial Number Date Code Reference (PDF, hosted by building-center.org)](https://building-center.org/wp-content/uploads/2017/08/Bradford-White-Serial-Number-Date-Code-Reference.pdf) (manufacturer or vendor document)
- [Bradford White: Is your water heater too old?](https://www.bradfordwhite.com/blogs/is-your-water-heater-too-old/) (manufacturer or vendor document)
- [ENERGY STAR: When should you replace your water heater?](https://www.energystar.gov/products/ask-the-experts/when-should-you-replace-your-water-heater) (government or regulatory source)
- [A. O. Smith: When to repair or replace your water heater](https://www.hotwater.com/info-center/when-to-repair-or-replace.html) (manufacturer or vendor document)
- [Rheem: Water heater lifespan, when to repair vs replace](https://www.rheem.com/water-heating/articles/water-heater-lifespan-when-to-repair-vs-replace/) (manufacturer or vendor document)

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Citation: OwnerSpec, "How old is my water heater? Reading the manufacture date from the serial number, brand by brand", https://ownerspec.com/plumbing/guides/water-heater-age-serial-number-date-code/, facts verified 3 October 2026.
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