Where our rules come from

Every supported serial format is recorded with its source and a published example. The decoder uses those rules in your browser; no AI interprets your serial. Source links, annotated examples and coverage limits are on each brand page. References reviewed 2026-10-26.

Documented rules. Visible limits.

Some serials encode only a week, so the displayed month is approximate. Repeating year codes show all possible dates with equal weight. Unrecognized formats get no guessed date. Manufacture date can precede installation and does not establish warranty coverage.

Read labels without removing sealed covers or touching wiring. Ask a service technician if a furnace label is inaccessible.

Repair or replace? How to decide

Typical lifespan is a planning range, not a diagnosis: tank water heaters about 10–12 years, tankless water heaters over 20 years, and central AC 10–15 years; furnaces 15–20 years. Maintenance, climate and water quality affect actual life.

The repair/budget note compares age with the lower end of the relevant range. This is our planning heuristic. Age alone cannot decide whether replacement is necessary. Consider service history, performance and a qualified technician’s repair quote before deciding. Compare repair and replacement costs before approving a major repair.

Brand names and logos identify navigation to independent serial guides. ApplianceAge is not affiliated with or endorsed by any manufacturer.