How we check a manufacture-date estimate

Serial Decoder interprets documented patterns; it does not query a manufacturer’s private serial-number database. A recognized pattern can suggest a date, but cannot authenticate equipment, establish ownership, confirm warranty coverage or assess its condition.

What happens to your serial

1. The calculator removes spaces and normalizes letters. It preserves the order of the characters and leading zeros.
2. Your selected brand determines which supported pattern is checked. A similar shape can occur in several brands, so we do not choose a brand automatically.
3. The date fields must fit the documented positions. Invalid months, invalid weeks and future dates are rejected.
4. Where a year code repeats, the tool lists candidates and leaves the single-year and age fields blank. It does not silently select the most recent decade.
5. The approximate age is the current calendar year minus the supported manufacture year. It is not a day-accurate age.

Evidence levels

A source-backed format means a manufacturer document describes that pattern for a stated product family. It does not mean every model bearing the same brand follows it. Each guide links its evidence and describes exclusions.

When the source is incomplete, the serial does not fit, or several interpretations remain, we recommend model-specific confirmation. Some listed brands have a verification guide rather than an automatic calculator. This is deliberate: an unsupported number should not become a confident date.

Corrections made September 28, 2026

• Corrected Carrier week/year positions, Lennox month letters, Rheem week/year order, GE starting letters, LG starting digits, and the documented Speed Queen month field.
• Replaced the incorrect universal Whirlpool month-letter claim with narrowly scoped numeric-year examples and explicit decade ambiguity.
• Separated ICP from York. Removed unsupported Trane decade-letter and other automatic rules that lacked reliable product-specific evidence.
• Removed unverified technician credentials and first-person field-experience claims. Replaced blanket “all brands” and accuracy promises with stated coverage limits.
• Added regression examples for supported formats and invalid inputs. Those checks establish consistent calculations, not manufacturer certification.

Manufacturer reference library

Report a correction

Use the contact page to send a source and a description of the conflicting format. Include the model family and country of sale. Avoid sending addresses, account identifiers or unredacted purchase documents. We review the source before changing a rule; one matching anecdote is not enough to generalize across a brand.