How Our Decoders Work

What happens when you press Check age, where every rule comes from and how sure we are about each brand.

Last updated 2026-10-18

What the tool does

1. Cleans up the serial. It converts letters to uppercase and removes spaces and dashes, so 2406-e 12345 and 2406E12345 are read the same way.
2. Tries every known format for that brand family. Each format is a precise pattern (for example "two digits, two digits, one letter, five digits") plus a rule for which characters hold the year and the month or week.
3. Rejects impossible dates. Month 13, week 60, a date in the future or a year outside the period a format was used all count as "no match" instead of a guess.
4. Handles repeating codes honestly. When a code repeats (letter years cycle every 20 years at Bradford White, single-digit years every decade at Trane), the tool first uses any clue the manufacturer documents, such as Bradford White's 7-digit (before December 2007) versus 8-digit sequence numbers. If two dates still fit, it shows the most recent one and tells you about the older one.
5. Compares the age with typical lifespan for the equipment type, using the table below.

All of this runs in your browser. The serial you type is never sent to our server.

Where the rules come from

In order of preference:

1. Manufacturer documents: serial nomenclature bulletins, product data, installation and warranty literature.
2. Distributor and contractor training material that reproduces the manufacturer's format.
3. Real data plates where the manufacture date is printed on the label or known from the install records.

Facts like "the first two digits are the week" can't be owned, but wording and tables can, so every explanation on this site is written from scratch.

Accuracy and verification status

Each brand family carries one of two labels. Verified means the rule correctly dated a set of real serials with known dates, and those serials are part of our automated tests. Being verified means the rule follows published references but we haven't finished checking it against real labels; results are shown with a note saying so.

Known limits

• Manufacture date isn't install date. Units typically sit in the supply chain for weeks or months before installation.
• Week-based serials are converted to a month using the ISO calendar, so a week-1 or week-52 unit can land a month either side.
• Older formats. Equipment built before the eras listed above often uses codes we don't read yet. The tool says so rather than guessing.
• Private-label and contractor brands are sometimes built by a different manufacturer than the name on the front, and follow that manufacturer's format.

Lifespan figures

The "share of typical life used" bar compares your unit's age with the middle-to-upper part of the typical range below. The ranges reflect published life-expectancy guidance from sources such as the US Department of Energy, ENERGY STAR and home-inspection industry tables, rounded to whole years.

Found a mistake?

Report it here. Corrections are tested, added to the test set and listed with a new review date in the table above.