How to read a Carrier, Bryant, Payne serial number (find the build date)

Decode a serial number now (works offline).

The rule

Digits 1–2 = week (01–53), digits 3–4 = year. Used for roughly the last 20+ years; older units use letters and single digits.

The maker doesn’t publish this rule where I could find it, so it rests on inspector and HVAC-guide sources and may be wrong for some units: InterNACHI inspectors’ forum (not the maker).

Worked examples

Applies to: Carrier, Bryant and Payne furnaces and air conditioners. Always check the result against the label.