This water heater age calculator decodes the serial number on your unit's rating plate to tell you the manufacture date — and whether your heater is near the end of its life. Most tank water heaters last 8 to 12 years; tankless units last 15 to 20. If yours is past that, replacing it on your schedule beats an emergency tank rupture and flooded floor. Decode it below, then see our Bellevue water heater repair: tank, tankless, and heat-pump page, or read tankless vs. storage water heaters in Bellevue.
Decoded from published manufacturer serial formats (sources below). Always confirm against the manufacture date on the unit's rating plate. Older or unusual serials may differ — pick “Other / not sure” to enter the year by hand.
Find the serial number on the rating-plate sticker on the side of the tank, then decode the manufacture date from it — every major brand hides the date inside the serial. The calculator above does this for you; the per-brand rules are below.
Most water heaters do not print the manufacture date in plain language. Instead, the date is encoded in the serial number using a brand-specific format. Once you know your brand's rule, the first few characters of the serial give you the month/week and year it was built.
If the sticker is faded or the serial looks unusual, choose "Other / not sure" in the calculator and enter the year printed on the plate by hand — some older and tankless units use formats the decoder doesn't cover.
A standard tank water heater lasts about 8 to 12 years; a tankless unit lasts 15 to 20 years with maintenance. Hard water and skipped annual flushing shorten both.
Once a tank heater passes 10–12 years, the risk of a tank rupture — and a flooded floor — climbs steeply. Replacing a heater that's near or past its lifespan on your own schedule is far cheaper and less stressful than an after-hours emergency replacement after the tank lets go.
Around Bellevue and the Eastside, water heaters in unconditioned garages and crawlspaces also work harder through cold winters, and the cold incoming groundwater means the burner or element runs longer per draw — both nudge real-world lifespan toward the lower end of the range.
Each manufacturer encodes the build date differently. Here are the formats for the most common brands in Bellevue homes — Bradford White, A.O. Smith, Rheem, Whirlpool, and State.
Bradford White: the serial begins with two letters. The first letter is the year (on a rotating 20-year cycle — e.g. "D" is 2007 or 1987), and the second letter is the month (A = January through M = December, skipping I).
A.O. Smith (and the State, Whirlpool, American, Reliance, and Kenmore units it builds): modern serials start with four digits — the first two are the year (e.g. "12" = 2012) and the next two are the week of that year.
Rheem and Ruud: on newer units the date sits right after the letter prefix — the first two digits are the week and the next two are the year (e.g. "…18 14…" = week 18 of 2014). Older and tankless Rheem units use different formats, so confirm against the rating plate.
State: since A.O. Smith acquired State in 2001, modern State serials follow the A.O. Smith year-then-week format; pre-2001 units start with a letter for the month followed by a two-digit year.
Repair a heater under about 8 years old if the failure is a part (thermostat, element, valve). Lean toward replacement once it's past 10–12 years, leaking from the tank, or needs a repair worth more than half a new unit.
A leaking tank is never a repair — once the steel tank corrodes through, the only fix is replacement. Rusty hot water, popping or rumbling noises, and recovery that keeps getting slower are all signs an older heater is near the end. If the calculator above puts your unit past its lifespan, it's worth getting a replacement quote before it fails.
Ready for a real, written flat-rate quote? These are the services behind the estimates above:
Deeper background on what drives these prices:
Serial-number formats are decoded from published manufacturer and inspection references. Always confirm against the date on your unit's rating plate.
Find the serial number on the rating-plate sticker on the side of the tank and decode the manufacture date from it — the date is encoded in the serial, not printed plainly. Use the calculator above (pick your brand and paste the serial), or read your brand's format in the section above. If in doubt, the manufacture date is sometimes also printed on the plate.
Bradford White serials start with two letters: the first is the year on a rotating 20-year cycle (for example, "D" = 2007 or 1987, "C" = 2006 or 2026) and the second is the month (A = January … M = December, skipping I). Paste the serial into the calculator above and it resolves the most likely year for you.
These share A.O. Smith's modern format: the first two digits of the serial are the year and the next two are the week. So a serial starting "1210" was built in week 10 of 2012. State and Whirlpool units built after 2001 follow the same rule.
A 12-year-old tank water heater is at the end of its typical 8–12 year life, so yes — start planning. It may run another year or two, but the failure mode for an old tank is a sudden rupture and a flooded floor, often at the worst time. Replacing on your schedule is cheaper than an emergency call. Tankless units last longer (15–20 years).
Yes. Home inspectors record the water heater's age, and a unit past its expected lifespan often becomes a negotiation point or a buyer-requested replacement. Knowing the age before you list — and replacing a clearly end-of-life unit — removes a common sticking point in Eastside home sales.
