Water heater age

Water heater serial number decoder: how old is your water heater?

Pick the brand, type the serial number from the water heater's label, and the decoder shows the month or week and year it was made. It covers tank, tankless and heat pump water heaters from 18 common brands.

Accuracy is not guaranteed.

This decoder gives an estimate based on how brands have coded serial numbers in the past. Manufacturers change their formats, and a serial can be misread, so the results may be wrong. Use them as a starting point only. Confirm with the date printed on the plate or with the manufacturer.

Where to find the serial number

Every water heater has a rating label with the model number, the serial number, the capacity and the gas or electric ratings. Many newer labels print the date outright, marked MFG. DATE, BUILD DATE or MONTH/YEAR. If yours does, that is your answer and there is nothing to decode.

  • Gas or electric tank. A rating label on the side of the tank, usually at eye level or above the gas control. If the tank sits in a closet, it may face the wall; a phone camera held at an angle often reaches it.
  • Heat pump water heater. A label on the side of the unit, often near the top.
  • Tankless. A sticker on the side or bottom of the case. Some list the serial on a second small sticker near the model number. Do not remove the front cover to look for it.
Rating label on the side of an A.O. Smith gas water heater, serial number outlined in red
Gas tank: a label on the side of the tank, above the gas control. This one prints a build date, 11/03/2021, so there's nothing to decode.
Rating label on the side of a Reliance electric water heater, serial number outlined in red
Electric tank: a label on the side of the tank. The serial, outlined, is next to the model number.
Rating label on an A.O. Smith heat pump water heater, serial number outlined in red
Heat pump water heater: a label on the side of the unit, with the serial near the top.
Serial number sticker on the side of a Navien tankless water heater, serial outlined in red
Tankless: a sticker on the side or bottom of the case. On this Navien the serial follows SN.

What the age tells you, and what it does not

The serial number tells you when the water heater was built. It does not tell you when it was installed, how hard the water is, whether it has been flushed, or how it is working today. Two water heaters built the same year can be in very different shape.

During a home inspection I report the approximate age of the water heater, along with what I can see of the tank, the venting, the relief valve and its discharge pipe, and the connections. The age is one piece of that report, not a verdict on the water heater.

Real Inspection Photos

Common Water Heater Findings

Real photos from Russ's inspection reports around Portland and Vancouver. Age is one clue; installation and condition problems like these are the rest.

  • Draft hood on a gas water heater shifted off center, leaving the flue opening partly exposed
    The draft hood had shifted off the flue. That can keep combustion gases from venting properly, a safety concern a qualified plumber should correct. Water heater findings in Portland inspections
  • Metal strap hanging loose beside an electric water heater instead of wrapped around the tank
    This tank was not secured with seismic straps. In an earthquake an unstrapped water heater can tip, break its connections, and cause water damage. Seismic risk in Portland area homes
  • Heavily corroded galvanized water pipe and fittings connected to a water heater
    The galvanized pipes at this water heater had heavy corrosion and small leaks. Pipes like these are usually due for replacement. Galvanized plumbing in Portland homes
  • White bucket placed under the end of a water heater relief valve discharge pipe
    A bucket under the relief valve pipe can mean the valve has been dripping. It's worth asking the sellers why it's there.
  • Green and white corrosion at a water fitting on top of a gas water heater
    Mineral crust and corrosion at this fitting point to an intermittent leak. Small drips like this can damage the tank top and surrounding area over time.

See a full sample report

Serial number formats by brand

Most brands have changed how they write serial numbers over the years, and several brands share a format because the same factories build them. Open a brand to see each format, with a made-up example showing which characters hold the date.

A.O. Smith / AO Smith4 formats

A.O. Smith serial number lookup and examples

Rating plate on an A.O. Smith gas water heater, serial number 2011118609451 outlined in red
A.O. Smith gas water heater plate from one of my inspections. The outlined serial reads as week 11 of 2020. The plate's printed date, BUILD DATE 03/17/2020, agrees.

  1. 4 digits for the year and week, then a letter and 6 digits or 9 more digits (about 2008 and later)

    Example1714A123456: Year 17, Week 14, Unit number A123456.

    Reads as week 14 of 2017. Used from 2005 to today.

    • The first 2 digits are the year and the next 2 are the week. Newer serials are 13 digits long and start the same way. A letter in front, if there is one, is skipped.

  2. 2 letters, 2 digits for the year, then 7 or more characters (before about 2008)

    ExampleGD99A123456: Factory G, Month D, Year 99, Unit number A123456.

    Reads as April 1999. Used from 1975 to 2008.

    • The first letter is the factory. The second letter is the month (A is January, M is December, no I) and the 2 digits after it are the year.

  3. A month letter, 2 digits for the year, then 6 or 7 more characters (before about 2010)

    ExampleC04A123456: Month C, Year 04, Unit number A123456.

    Reads as March 2004. Used from 1970 to 2010.

    • The letter is the month (A is January, M is December, no I) and the 2 digits after it are the year.

  4. A letter and 2 digits, a month letter, then 2 digits for the year (1960s to 1980s)

    ExampleB31K72123456: Prefix B31, Month K, Year 72, Unit number 123456.

    Reads as October 1972. Used from 1960 to 1989.

    • An older style, often printed with dashes. The second letter is the month and the 2 digits after it are the year.
American Standard2 formats

  1. A month letter, 2 digits for the year, then 4 to 6 digits

    ExampleE22123456: Month E, Year 22, Unit number 123456.

    Reads as May 2022. Used from 2015 to today.

    • Usually printed with a dash after the year. The letter is the month (A is January, M is December, no I).

  2. 21 digits (heat pump water heaters): the year and the day of the year come before the last 7 digits

    Example123456789221051234567: Prefix 123456789, Year 22, Day 105, Unit number 1234567.

    Reads as April 2022. Used from 2015 to today.

    • The 3 digits after the year are the day of the year, from 001 (January 1) to 365. The decoder turns that into a month.
American Water Heater / American / Proline2 formats

American Water Heater serial number lookup and examples

Rating plate on an American Water Heater gas tank, serial number 0332133124 outlined in red
American Water Heater gas tank plate from one of my inspections. The outlined serial reads as week 32 of 2003. The plate's printed date, MONTH/YEAR 08/2003, agrees.

  1. All digits, 9 or 10 long: year, then week

    Example0623123456: Year 06, Week 23, Unit number 123456.

    Reads as week 23 of 2006. Used from 1975 to today.

    • The first 2 digits are the year and the next 2 are the week.

  2. 4 digits for the year and week, then a letter and 6 digits or 9 more digits (about 2008 and later)

    Example1714A123456: Year 17, Week 14, Unit number A123456.

    Reads as week 14 of 2017. Used from 2005 to today.

    • The first 2 digits are the year and the next 2 are the week. Newer serials are 13 digits long and start the same way. A letter in front, if there is one, is skipped.
Bradford White3 formats

Bradford White serial number lookup and examples

Rating plate on a Bradford White gas water heater, serial number ZL52501103 outlined in red
Bradford White gas water heater plate from one of my inspections. The outlined serial reads as November 2023. No date is printed, but the 2019 standards year on the plate fits.

  1. 2 letters, then 8 digits (December 2007 and later)

    ExampleTK41234567: Year T, Month K, Unit number 41234567.

    Reads as October 2019. Used from 2007 to today.

    • The first letter is the year and the second is the month (A is January, M is December, no I). The unit number went from 7 digits to 8 in December 2007, which settles which 20-year cycle the year letter belongs to.

  2. 2 letters, then 7 digits (before December 2007)

    ExamplePC1234567: Year P, Month C, Unit number 1234567.

    Reads as March 1997. Used from 1984 to 2007.

    • The first letter is the year and the second is the month (A is January, M is December, no I). The year letters repeat every 20 years, so A to D can mean the 1980s or the 2000s. A standards year on the plate, such as ANSI Z21.10.1 with a year after it, rules out anything older than that year.

  3. Starts with OA, then 7 digits (January 1997 only)

    ExampleOA7654321: Year O, Month A, Unit number 7654321.

    Reads as January 1997. Used from 1997 to 1997.

    • A short run of serials started with the letter O by mistake. They were all made in January 1997.

Bradford White tankless units built by other companies may use those companies' serial styles. If the plate has no printed date, Bradford White can date the unit from the full serial number.

GE / General Electric2 formats

GE serial number lookup and examples

Rating plate on a GE electric water heater, serial number 0507R18938 outlined in red
GE electric water heater plate from one of my inspections. The outlined serial reads as May 2007. The plate's printed date, MFG. DATE 05/2007, agrees. Ignore the GE in front of the serial.

  1. Up to 4 letters, then 4 digits for the month and year (before about 2012)

    ExampleRH0710N54321: Prefix RH, Month 07, Year 10, Unit number N54321.

    Reads as July 2010. Used from 1980 to 2012.

    • Ignore the letters at the start. The first 2 digits are the month and the next 2 are the year.
    • Many plates also print a manufacture date near the serial number.

  2. Letters ending in a factory letter, then 4 digits for the week and year (about 2010 and later)

    ExampleRHM221912345: Prefix RH, Factory M, Week 22, Year 19, Unit number 12345.

    Reads as week 22 of 2019. Used from 2010 to today.

    • The letter right before the digits is the factory. The first 2 digits after it are the week and the next 2 are the year.
    • Many plates also print a manufacture date near the serial number.
Hotpoint2 formats

  1. Up to 4 letters, then 4 digits for the month and year (before about 2012)

    ExampleRH0710N54321: Prefix RH, Month 07, Year 10, Unit number N54321.

    Reads as July 2010. Used from 1980 to 2012.

    • Ignore the letters at the start. The first 2 digits are the month and the next 2 are the year.
    • Many plates also print a manufacture date near the serial number.

  2. Letters ending in a factory letter, then 4 digits for the week and year (about 2010 and later)

    ExampleRHM221912345: Prefix RH, Factory M, Week 22, Year 19, Unit number 12345.

    Reads as week 22 of 2019. Used from 2010 to today.

    • The letter right before the digits is the factory. The first 2 digits after it are the week and the next 2 are the year.
    • Many plates also print a manufacture date near the serial number.
Kenmore3 formats

  1. 4 digits for the year and week, then a letter and 6 digits or 9 more digits (about 2008 and later)

    Example1714A123456: Year 17, Week 14, Unit number A123456.

    Reads as week 14 of 2017. Used from 2005 to today.

    • The first 2 digits are the year and the next 2 are the week. Newer serials are 13 digits long and start the same way. A letter in front, if there is one, is skipped.

  2. All digits, 9 or 10 long: year, then week

    Example0623123456: Year 06, Week 23, Unit number 123456.

    Reads as week 23 of 2006. Used from 1975 to today.

    • The first 2 digits are the year and the next 2 are the week.

  3. A month letter, 2 digits for the year, then 6 or 7 more characters (before about 2010)

    ExampleC04A123456: Month C, Year 04, Unit number A123456.

    Reads as March 2004. Used from 1970 to 2010.

    • The letter is the month (A is January, M is December, no I) and the 2 digits after it are the year.

Kenmore water heaters were built by several companies over the years, so a Kenmore serial can follow another maker's style. Sears or the company named on the plate as the maker can help date it.

Navien3 formats

Navien serial number lookup and examples

Rating plate on a Navien tankless water heater, serial number 7414C1771171477 outlined in red
Navien tankless water heater plate from one of my inspections. The outlined serial reads as July 2017. The date starts at the 6th character: 17 for the year, 7 for July, then 11 for the day.

  1. 5 characters, then 2 digits for the year, a month code and 2 digits for the day

    Example5132B19X0512345: Prefix 5132B, Year 19, Month X, Day 05, Unit number 12345.

    Reads as October 2019. Used from 2009 to today.

    • The date starts at the 6th character. Months 1 to 9 are digits, and X, Y and Z stand for October, November and December. The 2 digits after the month are the day.

  2. 4 digits, then the full date written as year, month and day

    Example4321200907151234: Prefix 4321, Year 2009, Month 07, Day 15, Unit number 1234.

    Reads as July 2009. Used from 2006 to today.

    • Often printed with dashes around the date.

  3. 4 digits, then the 4-digit year, then 7 more digits

    Example432120081231234: Prefix 4321, Year 2008, Unit number 123.

    Reads as 2008. Used from 2006 to 2015.

    • An early style. It shows the year only.
Noritz1 format

  1. 12 digits: the 4-digit year, 2 for the month, then the unit number

    Example201403123456: Year 2014, Month 03, Unit number 123456.

    Reads as March 2014. Used from 1990 to today.

    • Usually printed with a period after the year and a dash after the month.
Reliance3 formats

Reliance serial number lookup and examples

Rating plate on a Reliance gas water heater, serial number 2123124675208 outlined in red
Reliance gas water heater plate from one of my inspections. The outlined serial reads as week 23 of 2021. The plate's printed date, BUILD DATE 06/08/2021, agrees.

  1. 4 digits for the year and week, then a letter and 6 digits or 9 more digits (about 2008 and later)

    Example1714A123456: Year 17, Week 14, Unit number A123456.

    Reads as week 14 of 2017. Used from 2005 to today.

    • The first 2 digits are the year and the next 2 are the week. Newer serials are 13 digits long and start the same way. A letter in front, if there is one, is skipped.

  2. A month letter, 2 digits for the year, then 6 or 7 more characters (older Reliance)

    ExampleK95123456: Month K, Year 95, Unit number 123456.

    Reads as July 1995. Used from 1970 to 2008.

    • These serials count from a business year that starts in October: A is October, B November, C December, D January, and so on to M for September. A, B and C units were made in the calendar year before the one in the serial. The decoder does that math for you.

  3. A factory letter, a month letter, 2 digits for the year, then 6 digits (older Reliance)

    ExampleAE01123456: Factory A, Month E, Year 01, Unit number 123456.

    Reads as February 2001. Used from 1970 to 2008.

    • Same business-year month code as the style above: A is October of the year before, D is January.
Rheem3 formats

Rheem serial number lookup and examples

Rating plate on a Rheem gas water heater, serial number M181807002 outlined in red
Rheem gas water heater plate from one of my inspections. The outlined serial reads as week 18 of 2018. The plate's printed date, MFG. DATE 01MAY2018, agrees. M is the factory letter: week 18 falls in early May.

  1. Up to 4 letters, then 4 digits for the month and year (before about 2012)

    ExampleRH0710N54321: Prefix RH, Month 07, Year 10, Unit number N54321.

    Reads as July 2010. Used from 1980 to 2012.

    • Ignore the letters at the start. The first 2 digits are the month and the next 2 are the year.
    • Many plates also print a manufacture date near the serial number.

  2. Letters ending in a factory letter, then 4 digits for the week and year (about 2010 and later)

    ExampleRHM221912345: Prefix RH, Factory M, Week 22, Year 19, Unit number 12345.

    Reads as week 22 of 2019. Used from 2010 to today.

    • The letter right before the digits is the factory. The first 2 digits after it are the week and the next 2 are the year.
    • Many plates also print a manufacture date near the serial number.

  3. 16 characters: a letter, 4 digits for the month and year, a letter, 9 digits and a letter

    ExampleK0316B123456789C: Prefix K, Month 03, Year 16, Unit number B123456789C.

    Reads as March 2016. Used from 1995 to today.

Most Rheem plates also print the manufacture date near the serial number. If yours does, use that date.

Richmond2 formats

  1. Up to 4 letters, then 4 digits for the month and year (before about 2012)

    ExampleRH0710N54321: Prefix RH, Month 07, Year 10, Unit number N54321.

    Reads as July 2010. Used from 1980 to 2012.

    • Ignore the letters at the start. The first 2 digits are the month and the next 2 are the year.
    • Many plates also print a manufacture date near the serial number.

  2. Letters ending in a factory letter, then 4 digits for the week and year (about 2010 and later)

    ExampleRHM221912345: Prefix RH, Factory M, Week 22, Year 19, Unit number 12345.

    Reads as week 22 of 2019. Used from 2010 to today.

    • The letter right before the digits is the factory. The first 2 digits after it are the week and the next 2 are the year.
    • Many plates also print a manufacture date near the serial number.
Rinnai2 formats

Rinnai serial number lookup and examples

Rating plate on a Rinnai tankless water heater, serial number LA.UA-001717 outlined in red
Rinnai tankless water heater plate from one of my inspections. The outlined serial reads as January 2019. L is the year letter for 2019 and A is January. The 2015 standards year on the plate fits.

  1. 4 letters, then 6 digits (2009 and later)

    ExampleKDAB123456: Year K, Month D, Unit number AB123456.

    Reads as April 2018. Used from 2009 to today.

    • Plates often print the first 2 letters apart from the rest, sometimes with a period after them. Type all of it. The first letter is the year (A is 2009) and the second is the month (A is January).

  2. All digits: 2 for the year, 2 for the month, then the unit number (1999 to 2008)

    Example0611123456: Year 06, Month 11, Unit number 123456.

    Reads as November 2006. Used from 1999 to 2008.

    • Often printed with a period after the year and a dash after the month.

On newer Rinnai plates the serial starts with 2 letters that are sometimes printed apart from the rest. Check that you typed those too.

Ruud3 formats

  1. Up to 4 letters, then 4 digits for the month and year (before about 2012)

    ExampleRH0710N54321: Prefix RH, Month 07, Year 10, Unit number N54321.

    Reads as July 2010. Used from 1980 to 2012.

    • Ignore the letters at the start. The first 2 digits are the month and the next 2 are the year.
    • Many plates also print a manufacture date near the serial number.

  2. Letters ending in a factory letter, then 4 digits for the week and year (about 2010 and later)

    ExampleRHM221912345: Prefix RH, Factory M, Week 22, Year 19, Unit number 12345.

    Reads as week 22 of 2019. Used from 2010 to today.

    • The letter right before the digits is the factory. The first 2 digits after it are the week and the next 2 are the year.
    • Many plates also print a manufacture date near the serial number.

  3. 16 characters: a letter, 4 digits for the month and year, a letter, 9 digits and a letter

    ExampleK0316B123456789C: Prefix K, Month 03, Year 16, Unit number B123456789C.

    Reads as March 2016. Used from 1995 to today.

State3 formats

State serial number lookup and examples

Rating plate on a State gas water heater, serial number 2002117747446 outlined in red
State gas water heater plate from one of my inspections. The outlined serial reads as week 2 of 2020. No date is printed, but the 2017 standards year on the label fits.

  1. 4 digits for the year and week, then a letter and 6 digits or 9 more digits (about 2008 and later)

    Example1714A123456: Year 17, Week 14, Unit number A123456.

    Reads as week 14 of 2017. Used from 2005 to today.

    • The first 2 digits are the year and the next 2 are the week. Newer serials are 13 digits long and start the same way. A letter in front, if there is one, is skipped.

  2. A month letter, 2 digits for the year, then 6 or 7 more characters (before about 2010)

    ExampleC04A123456: Month C, Year 04, Unit number A123456.

    Reads as March 2004. Used from 1970 to 2010.

    • The letter is the month (A is January, M is December, no I) and the 2 digits after it are the year.

  3. 2 letters, 2 digits for the year, then 7 or more characters (before about 2008)

    ExampleGD99A123456: Factory G, Month D, Year 99, Unit number A123456.

    Reads as April 1999. Used from 1975 to 2008.

    • The first letter is the factory. The second letter is the month (A is January, M is December, no I) and the 2 digits after it are the year.
Takagi1 format

  1. 4 digits for the year and week, then a letter and 6 digits or 9 more digits (about 2008 and later)

    Example1714A123456: Year 17, Week 14, Unit number A123456.

    Reads as week 14 of 2017. Used from 2005 to today.

    • The first 2 digits are the year and the next 2 are the week. Newer serials are 13 digits long and start the same way. A letter in front, if there is one, is skipped.

Takagi units made before about 2010 use a plain counting number with no date in it. For those, Takagi can look up the date from the serial number, or a standards year printed on the plate gives the earliest possible year.

U.S. Craftmaster2 formats

U.S. Craftmaster serial number lookup and examples

Rating plate on a U.S. Craftmaster electric water heater, serial number 9402305649 outlined in red
U.S. Craftmaster electric water heater plate from one of my inspections. The outlined serial reads as week 2 of 1994. The label prints YEAR WEEK right under the serial.

  1. All digits, 9 or 10 long: year, then week

    Example0623123456: Year 06, Week 23, Unit number 123456.

    Reads as week 23 of 2006. Used from 1975 to today.

    • The first 2 digits are the year and the next 2 are the week.

  2. 4 digits for the year and week, then a letter and 6 digits or 9 more digits (about 2008 and later)

    Example1714A123456: Year 17, Week 14, Unit number A123456.

    Reads as week 14 of 2017. Used from 2005 to today.

    • The first 2 digits are the year and the next 2 are the week. Newer serials are 13 digits long and start the same way. A letter in front, if there is one, is skipped.
Whirlpool2 formats

  1. 4 digits for the year and week, then a letter and 6 digits or 9 more digits (about 2008 and later)

    Example1714A123456: Year 17, Week 14, Unit number A123456.

    Reads as week 14 of 2017. Used from 2005 to today.

    • The first 2 digits are the year and the next 2 are the week. Newer serials are 13 digits long and start the same way. A letter in front, if there is one, is skipped.

  2. All digits, 9 or 10 long: year, then week

    Example0623123456: Year 06, Week 23, Unit number 123456.

    Reads as week 23 of 2006. Used from 1975 to today.

    • The first 2 digits are the year and the next 2 are the week.

Questions about reading water heater serial numbers

Why did I get more than one date?

Some brands reuse the same letter codes every 20 years. Bradford White is the best-known example: an older serial starting with A can mean 1984 or 2004. When a serial fits more than one date, the decoder shows all of them instead of guessing. Look for a standards year on the label, such as ANSI Z21.10.1 followed by a year. The water heater cannot be older than that year.

The decoder says no match. What now?

First check that you typed the serial number, not the model number, and that you included any letters at the start. Then look for characters that are easy to mix up, like the letter O and a zero. On some tankless units the first letters of the serial are printed apart from the rest; type all of them. A few older units, like Takagi models from before about 2010, have no date in the serial at all. If the label has no printed date, the maker's customer service line can usually look it up from the serial number.

Is the date it was made the same as the date it was installed?

Not always. A water heater can sit in a warehouse for months before it goes in. An installer's sticker, a permit tag, or permit records for the address can show when it was put in.

How accurate is the decoder?

The accuracy of the results is not guaranteed. The rules come from how each brand has coded dates over the years, and they were checked against water heater labels from my own inspections, including dozens that print their own build date. Manufacturers do change formats, though, and a few old formats are only partly known. A date printed on the label always wins, and the manufacturer can confirm the date from the serial number.

Does it work for furnaces and air conditioners?

Not this one. Heating and cooling equipment follows its own rules. Use the HVAC serial number decoder for furnaces, air conditioners, heat pumps and ductless units.

Buying a home in the Portland area?

A home inspection covers the water heater along with the rest of the house, including its approximate age and visible condition. Serving the Portland metro and Southwest Washington, seven days a week.

Schedule online Call (971) 202-1311