This article is a quick reference guide for determining the age of common water heater and boiler manufacturers. Most manufacturers do not clearly state the year of manufacture on the data plate. Instead, the date is typically encoded in the serial number.

By identifying the manufacturer and correctly decoding the serial number, the equipment’s age can usually be determined. Because manufacturers have changed formats over time, verification with the manufacturer is always recommended, especially for insurance, real estate, or warranty purposes.

Serial numbers may encode:

• Year (and sometimes month) of manufacture
• Manufacturing plant
• Model or unit type
• Production sequence

For inspection purposes, the year of manufacture is typically the most important data point and is the focus of this guide.

Water Heater Life Expectancy (Important)

• Tank-type gas or electric water heaters: typically 8–12 years
• Well-maintained tank units: may reach 12–15 years in some cases
• Tankless water heaters: typically 15–20 years with proper maintenance

Service life can sometimes be extended by replacing components such as heating elements, anode rods, or gas valves, but age and corrosion remain limiting factors.

How old is my American water heater? See AO Smith.
How old is my AO Smith water heater?
How old is my Apollo water heater?
How old is my Bosch water heater?
How old is my Bradford White water heater?
How old is my General Electric or GE water heater?
How old is my GSW water heater? See AO Smith
How old is my Navien water heater?
How old is my PowerStar water heater? See Bosch
How old is my Rheem water heater?
How old is my Ruud water heater?
How old is my Rinnai water heater?
How old is my State Industries water heater?
How old is my Takagi water heater?
How old is my US Craftmaster water heater? See AO Smith
How old is my Weil-McLain boiler?
How old is my Whirlpool water heater? See AO Smith

Water Heaters

American

See AO Smith

AO Smith 

Y=year of manufacturer  X=letter  7=numbers
The year of manufacture for AO Smith water heaters is encoded in the serial number.

The year of manufacture is encoded in the serial number. The first two digits typically indicate the year.

Common formats:

• YY77X7777777
• YY77777777777
• YY777 77777

Note: Older units may include letters before the numeric year code. Some models also encode the week of manufacture.

Apollo

Y=year of manufacturer  X=letter  7=numbers
The year of manufacture for Apollo water heaters is encoded in the serial number.

XYYX77777 (1st and 2nd numbers of the serial number indicate the year of manufacture)

Note: Older units may have additional letters before the 1st and 2nd numbers

Bosch

Y=year of manufacturer  X=letter  7=numbers
The year of manufacture for Bosch water heaters is encoded in the serial number.

Bosch serial numbers vary widely by model and generation, especially between tank and tankless units.

• Many Bosch tankless units use a YYMM or YYYYMM date format
• Some older or specialty models cannot be reliably dated from the serial number alone

Recommendation: When the date is unclear, contact Bosch directly at 800‑283‑3787 or use Bosch’s official serial number lookup tools.

Bradford White

Y=year of manufacturer  X=letter  7=numbers
The year of manufacture for Bradford White water heaters is encoded in the serial number.

YX7777777 (The 1st letter of the serial number indicates the year of manufacture)

A=2004  B=2005  C=2006  D=2007  E=2008  F=2009  G=1990/2010  H=1991/2011  J=1992/2012  K=1993/2013  L=1994/2014
M=1995/2015  N=1996/2016  P=1997/2017  S=1998/2018  T=1999/2019  W=2000/2020  X=2001/2021  Y=2002/2022  Z=2003/2023

General Electric or GE

Y=year of manufacturer  X=letter  7=numbers
The year of manufacture for General Electric water heaters is encoded in the serial number.

GE no longer manufactures water heaters. Most GE-branded water heaters were manufactured by AO Smith.

Common formats:

• 77YY000000 (3rd and 4th digits indicate year)
• XX77YY777777

Gas units may appear as:

• GENG77YYX77777

Note: Because formats vary, many GE units should be dated using AO Smith conventions.

GSW

See AO Smith

Navien

Y=year of manufacturer  X=letter  7=numbers
The year of manufacture for Navien water heaters is encoded in the serial number.
Most Navien water heaters encode the full four‑digit year, often along with the month.
Some older serials may use a two‑digit year, but YYYY formats are most common.

7777-YYYY7777-7777  (5th, 6th, 7th, and 8th numbers of the serial number indicate the year of manufacture)
7777-YYYY-777-7777  (5th, 6th, 7th, and 8th numbers of the serial number indicate the year of manufacture)

7777XYY77777777        (5th and 6th numbers after a letter of the serial number indicate the year of manufacture)
7777XYYX7777777        (5th and 6th numbers after a letter of the serial number indicate the year of manufacture)

Rheem or Ruud

Rheem and Ruud water heaters typically use a month and year (MMYY) format in the serial number.

• MM = month
• YY = year

Example: 0619 = June 2019

Other formats exist on older or specialty units, so manufacturer confirmation may be needed if the date is unclear.

Rinnai

Y=year of manufacturer  X=letter  7=numbers
The year of manufacture for Rinnai water heaters is encoded in the serial number.

2009 and later  Y7. CA-777777   (1st letter of the serial number indicates the year of manufacture)
A=2009  B=2010  C=2011  D=2012  E=2013  F=2014  G=2015  H=2016  J=2017  K=2018  L=2019  M=2020  N=2021  P=2022  Q=2023 R=2024 S=2025 T=2026

before 2009    YY. 77-77777       (1st and 2nd numbers of the serial number indicate the year of manufacture)

State Industries

Y=year of manufacturer  X=letter  7=numbers
The year of manufacture for State Industry water heaters is encoded in the serial number.

State water heaters are manufactured by AO Smith.

Common formats:

• YY77X777777
• XYY77X777777

The first two digits of the year code indicate the year of manufacture.

Takagi

Call 888-882-5244 with the serial number.

US Craftmaster

Y=year of manufacturer  X=letter  7=numbers
The year of manufacture for US Craftmaster water heaters is encoded in the serial number.

US Craftmaster water heaters are manufactured by AO Smith.

Format:

• YY7777777

The first two digits indicate the year of manufacture.

Whirlpool

Y=year of manufacturer  X=letter  7=numbers
The year of manufacture for Whirlpool water heaters is encoded in the serial number.

Whirlpool water heaters are manufactured by AO Smith and generally follow AO Smith serial‑number conventions.

Format:

• YY77X777777

Serial numbers may or may not include letters, depending on the production year.

Boilers

How Old Is My Boiler?

Most boiler manufacturers do not clearly state the manufacturing year on the data plate or label, but the year of manufacture is typically coded in the serial number.  By referencing the manufacturer below and the equipment’s serial number, the equipment’s age can be determined in most cases.

Weil McLain

The CP number is found on a white sticker on the boiler.  The year of manufacture for Weil McLain boilers is encoded in the CP number.  Or call 219 879-6561 or 866 783-9276.  The company also has a CP number lookup page here.

Pre- 2000  —  1414001-3810000
2000  —  3810001-4055000
2001  —  4055001-4311000
2002  —  4311001-4586999
2003  —  4587000-4807000
2004  —  4807001-5047000
2005  —  5047001-5301000
2006  —  5301001-5454497
2007  —  5454498-5721063
2008  —  5731064-5957346
2009  —  5957347-6150483
2010  —  6150484-6368018
2011  —  6368019-6555277
2012  —  6555278-6779489
2013  —  6779490-6998292
2014  —  6998293-7209932
2015  —  7209933-7429423
2016  —  7429424-7493025
2017  —  7493026-7629669
2018  —  7629670-7729057
2019  —  7729058-7782025
2020  —  7782026-7880529
2021  —  7880530-7961367
2022  —  7961368-7991517
2023 — 7991518-8120013
2024 — 8120014-8199005
2025 — 8199006-