How Old Is My Water Heater? Age by Serial Number
Type the serial number from the label and get the build year, the age against the typical 6-to-12-year tank life, and what to ask a plumber.
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Manufacturer serial formats (public technical references), compiled 2026-09 · Updated September 2026
How water heater serial numbers encode the date
Three makers, three different codes
Bradford White uses two letters: the first is the year on a 20-year cycle and the second is the month. Rheem, Ruud and Richmond print the month then the year in the first four digits after any letters. A.O. Smith, State, American and the store brands they build print the year then the week. The same four digits mean different things on different labels, which is why the tool asks for the brand first.
Why a tank has a shorter clock than a furnace
A storage tank is steel with a glass lining and a sacrificial anode rod. Once the anode is used up the water goes after the steel, and the tank fails from the inside out. InterNACHI puts a conventional tank at 6 to 12 years and a tankless unit at 10 to 20 with regular descaling. Past ten years, a tank in a finished space or above living areas is a flood waiting for a date.
The 20-year letter problem
Bradford White reuses its year letters every 20 years, so D means 1987 or 2007 and M means 1995 or 2015. The tool lists both and asks which decade the heater was installed. Two tiebreakers help: an 8-digit sequence after the letters means late 2007 or newer, and the ANSI standard year on the label is the earliest the unit could have been built.
Common questions
On a sticker or metal plate on the side of the tank, usually near the gas control or the electrical access cover. Tankless units carry it on the side or bottom of the case or inside the front cover. The same label lists the model number and, on newer units, the manufacture date.
The first letter is the year and the second is the month. DG6322957 reads D for 2007 (or 1987) and G for July. Year letters skip I, O, Q, R, U and V, and month letters run A to M skipping I.
After any letter prefix, the first two digits are the month and the next two the year. 0804B10488 was built in August 2004 and RHLN0106534307 in January 2006. Newer styles put the week first, and the tool tries each published layout in turn.
A conventional storage tank typically lasts 6 to 12 years and a tankless unit 10 to 20 years with regular maintenance (InterNACHI chart). Hard water, a never-replaced anode rod and a tank that was never flushed pull the number down.
At 12 years a tank is at the top of its typical range. If it sits above finished space, shows rust at the bottom seam or the fittings, or the anode rod was never replaced, a planned replacement beats an emergency one. Ask a plumber to check the anode, the seams and the relief valve and to say what a like-for-like swap would involve.
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