Water heater age decoder

How to find out how old your water heater is

Water heater makers hide the manufacture date in the serial number. Find the rating label on the side of the tank (on gas models it’s usually near the gas valve; on electric models, near the access panels). Copy theserial number, not the model number, and pick the brand printed on the label. Some newer labels also print the manufacture date outright; if yours does, that wins.

The result is the manufacture date, not the day the tank was installed. A water heater can sit in a warehouse or a store before it goes into a house, so it was installed some time after this date.

How each brand writes the date

Each brand page explains its rules in full, with more worked examples.

Why a serial can give more than one year

Bradford White uses letters for the year and runs through its alphabet every 20 years, so the same letter means 1987 and 2007 [1][2]. Where the serial alone can’t settle it, this decoder shows every possible year instead of guessing, and says what on the label tells them apart. Week-coded serials give the week; the month shown next to it is approximate.

Each result also says how well the rule is supported. Every rule used for water heaters is confirmed by at least two independent sources, such as the manufacturer’s own guide, InterNACHI’s dating chart and the Building Intelligence Center’s brand pages. Where sources disagree (for example, one chart reads A.O. Smith’s month letter J as October), we say so.

What this decoder doesn’t cover

• Brands outside the five above, such as GE, American, Lochinvar, Rinnai and Bosch.
• Bradford White oil-fired (Aero) and tankless units, and older A.O. Smith styles such as “A20-H-78”.
• Rheem tankless serials and some newer Rheem labels that start with a week number. Only one source describes these.

Common questions

How can I tell how old my water heater is?

Read the serial number on the rating label and decode it with the tool above. The brand pages show where each maker puts the year and month, so you can also do it by hand.

Is the date in the serial number the install date?

No. It’s when the tank was built. Installation came later, by weeks or sometimes much longer.

My serial shows two possible years. Which is right?

Usually the tank itself tells you: one date is often decades old. On Bradford White tanks, 7 digits after the letters means the tank was made before December 2007 and 8 digits means after [1], and the ANSI standard year on the label helps with the rest [2].

My brand isn’t listed. Can I still date it?

Sometimes. Ruud tanks use Rheem’s code. Whirlpool tanks are built by American Water Heater, and State is part of A.O. Smith, so those families share date codes [4][3][7]. Otherwise, check the label for a printed date or ask the manufacturer.

How long will my water heater last?

That depends on water quality, how hard the tank works and how it has been maintained, so we don’t give a lifespan figure. The age from this tool is a useful starting point when you talk to a plumber.

Brand pages

• Bradford White water heater age: Year and month letters, the 20-year cycle, 7 vs 8 digits and “OA” serials.
• A.O. Smith water heater age: Year + week (about 2008 on) and month letter + year (older tanks).
• State water heater age: State (an A.O. Smith brand): year + week, or month letter + year.
• Whirlpool water heater age: Built by American Water Heater: year + week in the first four digits.
• Rheem and Ruud water heater age: Skip the letter prefix; the first four digits are month + year.

Not affiliated with any water heater manufacturer. Brand names are used only to say which serials the decoder reads.

Sources

1. Bradford White (For The Pro site): Determining The Age Of A Water HeaterUsed for: Two letters + 7 digits (before December 2007); Two letters + 8 digits (December 2007 on); "OA" serials (factory computer error).
2. Building Intelligence Center: Bradford White Water Heater AgeUsed for: Two letters + 7 digits (before December 2007); Two letters + 8 digits (December 2007 on); "OA" serials (factory computer error).
3. InterNACHI (International Association of Certified Home Inspectors): InterNACHI Water Heater Dating ChartUsed for: Two letters + 7 digits (before December 2007); Month letter + two-digit year (before about 2008); Year + week first; Month + year after any letter prefix.
4. Energy Trust of Oregon: Serial Number Decoder: Water Heater (PDF)Used for: Two letters + 7 digits (before December 2007); Year + week first (about 2008 on); Month letter + two-digit year (before about 2008); Year + week first; Month + year after any letter prefix.
5. Honest Home Inspections, LLC (hosted by InspectAPedia): How to determine Water Heater and Furnace Age (PDF, last updated 2009-01-06)Used for: Two letters + 7 digits (before December 2007); Month letter + two-digit year (before about 2008); Year + week first; Month + year after any letter prefix.
6. Building Intelligence Center: A.O. Smith Water Heater AgeUsed for: Year + week first (about 2008 on); Month letter + two-digit year (before about 2008).
7. Building Intelligence Center: STATE Water Heater AgeUsed for: Year + week first (about 2008 on); Month letter + two-digit year (before about 2008).
8. Building Intelligence Center: Whirlpool Water Heater AgeUsed for: Year + week first.
9. Rheem Manufacturing: How to locate and read your Rheem water heating serial numbersUsed for: Month + year after any letter prefix.
10. InspectAPedia: Rheem Water Heater Age DecoderUsed for: Month + year after any letter prefix.
11. Building Intelligence Center: Rheem Water Heater AgeUsed for: Month + year after any letter prefix.