On the rating label on the side of the tank, usually near the top and next to the yellow EnergyGuide sticker. It is marked Serial No. or S/N. Tankless units have the label on the side or bottom of the cabinet.
Inside the front access panel, on the side of the cabinet or on the blower housing. Many plates also print the manufacture date outright.
On the plate on the outdoor unit, usually on the side near where the refrigerant lines and electrical connections enter.
Almost never. The model number describes the product; the serial number identifies the individual unit and carries the date. Use the serial.
Some makers encode the year as a letter that repeats every 20 years or so (Bradford White, York before 2004), or as a single digit with no decade (Mitsubishi, LG). The serial alone cannot say which cycle, so we show every possibility instead of guessing.
It is the year of the safety standard the unit was certified to, not the build date. It is a floor: the unit was built in that year or later. It helps pick between two possible years.
Use the printed date. It is the maker's own statement. The serial decode exists for the many labels that do not print one.
No. Age tells you where the unit sits in its typical life. Rust, leaks, noise, repair history and water quality move the real answer in either direction. Treat the verdict as a planning tool.
Each rule is checked against at least two independent published sources where possible. Rules confirmed by one source only are marked. Where sources disagree, the result says so and shows both readings.
Check that you have the serial and not the model number, that the brand is right, and that no character was misread (0 and O, 1 and I, 5 and S are the usual mix-ups). If it still fails, the maker's customer service can date the unit from the serial.
A metal rod inside a tank water heater that corrodes instead of the steel tank. Once it is used up, the tank starts to rust. Replacing it at year 4 to 6 is the single cheapest way to extend a tank's life.
Somewhat. A 12-year tank often has a bigger or second anode rod and sometimes a thicker lining. It will tend to last longer than a 6-year tank, but the warranty is a floor the maker is comfortable with, not a forecast.
Not because of age alone. The risk is a cracked heat exchanger, which can leak combustion gases. Have it inspected each fall and keep a carbon monoxide alarm on every level.
The refrigerant in most air conditioners and heat pumps built before 2010. Its production ended in 2020, so recharging a leaking R-22 system is expensive and only buys time. A refrigerant leak on an R-22 unit usually means replacement.
Most U.S. tank water heaters come from three companies. A.O. Smith makes A.O. Smith, State, American, Whirlpool, U.S. Craftmaster, Reliance, Kenmore, Lochinvar and Takagi. Rheem makes Rheem, Ruud, Richmond, GE (tank), Marathon and Paloma. Bradford White makes its own. That is why many brands share the same serial format.
The age you just looked up is the kind of fact that gets lost. A written record of serial numbers, install dates, repairs and who did the work saves the next owner, inspector or insurer from guessing.
A lifetime logbook for the house, organized by system, with room for serial numbers, install dates, repairs and contractors. It stays with the house for the next owner.
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