Water heater age drives the most important question a homeowner faces when something goes wrong: repair or replace. The serial number is the only reliable source. Yellow installation stickers fade, fall off, or get installed with the wrong date. Owner memory rarely matches reality. The serial number was stamped at the factory and tells the truth.
The serial number lives on a manufacturer label, usually a white or silver sticker, mounted on the side of the tank near the top. Rheem and Bradford White typically place it on the upper third of the tank facing the front. AO Smith and State tend to put it on the side near the gas valve or near the T&P valve. Tankless units have the label on the side or bottom of the unit chassis.
Rheem, Ruud, and Richmond share a serial code system. Modern format uses a 4-digit week/year code in the first four characters of the serial number. The first two digits are the week of manufacture (01–52). The next two are the year. Example: a serial starting with 4319 was manufactured in week 43 of 2019, roughly late October.
Older Rheem units used a different format with letter codes. If the serial does not start with four digits, the unit is likely pre-2007 and would be 18+ years old by 2026. Almost always replacement candidates regardless of current symptoms.
Bradford White uses a unique two-letter prefix on its serial numbers. The first letter is the year on a 20-year cycle. The second letter is the month using A=January, B=February, C=March, D=April, E=May, F=June, G=July, H=August, J=September (skipping I), K=October, L=November, M=December.
The year cycle: A=1984/2004, B=1985/2005, C=1986/2006, D=1987/2007, E=1988/2008, F=1989/2009, G=1990/2010, H=1991/2011, J=1992/2012, K=1993/2013, L=1994/2014, M=1995/2015, N=1996/2016, P=1997/2017, R=1998/2018, S=1999/2019, T=2000/2020, W=2001/2021, X=2002/2022, Y=2003/2023, Z (next cycle).
Use age and condition to disambiguate the 20-year cycle. A Bradford White starting with "MF" is either May 1995 or May 2015. A unit physically present in 2026 starting with MF is almost certainly the 2015 build.
A.O. Smith and its sister brands State and Reliance share serial code logic. The first two digits of the serial number indicate the year of manufacture. The next three digits indicate the day of the year (001–365). Example: serial starting with 19245 indicates day 245 of 2019, roughly early September.
Format has shifted slightly over the years. If the first two digits don't match a plausible year, look for a 4-digit year embedded later in the serial.
Rinnai. Modern Rinnai tankless serial numbers begin with a two-digit year code. A serial starting with 19 indicates 2019 manufacture. The next character or characters indicate month and production run. The label is on the side of the chassis.
Navien. Navien serial numbers contain a manufacture date in YYYYMM format embedded after a brand prefix. Example: a serial containing 201907 indicates July 2019. The label is on the side or bottom of the unit.
Big-box water heaters sold under GE, Whirlpool, and Kenmore brands are manufactured by Rheem or A.O. Smith. The actual manufacturer is often visible in fine print on the label. Once identified, decode the serial using the actual manufacturer's system from above.
Under 5 years. Almost always repair, not replace. Tanks this young that fail a single component are repair candidates. Replacement at this age is rare unless the tank has already developed a bottom leak.
5–10 years. Repair is usually the right call unless the tank itself is failing (bottom or side leak, rust-colored water). Single component failures get fixed; tank failures get replaced.
10–15 years. Case-by-case. A 12-year-old tank with a single failed thermocouple may still get a few years out of repair. The same tank with a dripping bottom is replacement only.
15+ years. Replacement almost always makes more sense. The tank has lived past its expected lifespan; further repair investment usually doesn't pay back.
For repair details, see tank water heater repair Kansas City. For replacement, see water heater installation. For comparing tank vs tankless at replacement time, see the cost comparison.
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