How Old Is My Water Heater? Find the Age From Your Serial Number

Your water heater’s age is hidden in its serial number — there is no build date printed in plain English on most units. Find the rating plate sticker on the side of the tank, copy down the serial number, and match it to your brand below. It takes about thirty seconds.

Nearly every brand falls into one of three systems:

Most tanks last 10 to 12 years. If yours is past that, the age matters more than any symptom — see what your number actually means further down.

The rating plate is a metallic or paper label on the side of the tank, usually at eye level or just below. On tankless units it is on the bottom or right side panel. It lists the manufacturer, model number, serial number, capacity, and input rating.

You want the line marked Serial No. or Serial Number — not the model number. If the sticker is faded or peeling, try a photo with your phone flash; the embossed digits often read better in a picture than in person.

Not sure what you are looking at? Our rating plate and model number guide shows where every brand puts its label.

These brands all come out of the same A.O. Smith family and share one system: the first two digits are the year, the next two are the week of that year. The rest is a production sequence number you can ignore.

Two digits for a week is not intuitive, so here is the quick conversion. Treat it as approximate — a week that straddles a month boundary can land either side depending on the year:

A note on the year digits. Two digits are ambiguous, so read them in context: 80–99 means the 1980s or 1990s, and anything from 00 up to the current year is the 2000s. A serial starting 97 is 1997, not 2097 — and a tank that old was replaced long ago in almost every case. One caveat: this rule only applies when the serial starts with four digits. Many A.O. Smith, State and Reliance units built before roughly 2008 begin with a letter instead, and the year sits after it.

Older American and State units sometimes use a letter for the month followed by a two-digit year instead. If your serial starts with a letter, use the Bradford White month letters below (A = January, B = February, and so on) and read the digits that follow as the year.

Rheem and the brands it builds for flip the order: the first two digits are the month, the next two are the year. This is the single most common mix-up we see, because the same four digits mean completely different things depending on the brand.

Strip the letters first. Many Rheem-family serials start with a brand or fuel prefix such as RH, RN or GE. Ignore those and read the first four digits. And note one exception: on some Rheem lines — heat-pump and certain electric models — a single plant letter is followed by a week code instead, so a serial like A5214 is week 52 of 2014, not month 52. If the first two digits are larger than 12, you are looking at a week.

Kenmore is a rebadge, and the model prefix does not tell you who built it — every Kenmore water heater model starts with 153, because that is simply Sears’ category code. In practice Kenmore tanks came from the A.O. Smith side of the industry, so read them year-then-week like the group above. Units from roughly 2008 to 2018 follow that rule; older ones use a letter for the month followed by the year. Kenmore water heaters were discontinued around 2018, so nothing new is being built.

Bradford White uses letters instead of digits: the first letter is the year, the second is the month. The codes below come from Bradford White’s own published date-code chart.

Year codes (first letter)

Month codes (second letter)

The letters I, O, Q, R, U and V are skipped in year codes, and I is skipped in months — they are too easily confused with digits. Because the year letters repeat on a twenty-year cycle, pair the code with the unit’s condition: a tank in daily use today is the recent date, not the one from the 1980s.

Tankless units last longer than tanks — commonly 15 to 20 years with descaling — so age alone is a weaker signal. Error codes tell you more; see our error code guide for every brand.

Manufacturers put a standard tank at 8 to 12 years; the US Department of Energy gives a slightly wider 10 to 15. Either way, once you are past a decade you are into the tail. Hard water shortens it and a neglected anode rod shortens it further, while an annual flush helps. Softened water is a genuine trade-off rather than a straight win: it cuts scale, but it also raises the water’s conductivity and strips away the thin protective film of scale on the steel, which consumes the anode rod faster. A.O. Smith says as much in its own technical bulletin. If you run a softener, have the anode checked more often, not less. Tankless units run 15 to 20 years, though that assumes descaling on a regular schedule.

The reason age matters so much: the steel corrodes from the inside where nobody can see it, so the final breach tends to be sudden. That does not mean there is no warning at all — rusty or smelly hot water, rumbling from sediment, and a shrinking supply of hot water all say the inside of the tank is going. What you never get is a countdown. That is why we push replacement before failure: the heater costs the same either way, but the water damage does not.

Found a date older than you hoped?

We will tell you honestly whether yours has years left or is due — and quote a replacement while it is still your choice.

Tank warranties commonly run six, nine, ten or twelve years. Coverage normally starts from the installation or purchase date, if you can document it — and that is the catch. Without a receipt or an install record, manufacturers fall back to the manufacture date encoded in the serial you just decoded. Rheem adds ninety days to it; Bradford White uses installation or manufacture-plus-six-months, whichever comes first. So a unit that sat in a warehouse can quietly cost you months of coverage if the paperwork is gone.

This matters most when a tank has failed early. A seven-year-old heater with a twelve-year warranty means the replacement tank itself is supplied at no charge. Most warranties also include a short labor allowance — often one to three years — but past that you pay the labor, and freight, disposal of the old unit, permits and any code-required upgrades sit outside the warranty regardless. Bring the model and serial number to the conversation — no manufacturer will process a claim without both.

Not sure what yours came with? Send us the numbers off the plate and we will look it up. See also what a replacement actually costs and the 10 signs it is time to replace.

Know the age. Now know your options.

Repair, replace, or leave it alone — we will give you the straight answer. Licensed, permitted techs serving Oregon, Washington and California.

Water on the floor right now? Read what counts as an emergency first.