Serial number vs model number
The decoder needs the serial number. The model number tells you what the unit is, not when it was built.
A model number identifies a product line, size and configuration; every unit of that model shares it. A serial number is unique to one unit, and for the brands on this site it embeds the build week or month and year. On most plates the two sit next to each other, labelled M/N and S/N, MODEL and SERIAL, or similar.
Two things trip people up. First, the same visual shape means different things at different makers: a 10-character serial of four digits, a letter and five digits is week-year-plant at Carrier and plant-year-month at Lennox (both per building-center.org). Second, some brands changed format mid-year, so a serial can match two eras; Trane's 2002 to 2009 style used one leading year digit and its 2010 style two, and York switched formats in October 2004. Brand pages show every era and the decoder evaluates all of them.
Worked examples from the tables
| Brand | Serial | Decodes to |
|---|---|---|
| Carrier | 4006A17330 | week 40 of 2006 |
| Carrier | 850304091 | March 1985 |
| Carrier | A167890 | January 1971 |
| Carrier | 46U152456 | week 46 of 1967 |
| Trane | 130313596L | week 3 of 2013 |
| Trane | 91531S41F | week 15 of 2009 |
| Trane | F23456789 | week 23 of 1991 |
| Lennox | 5899L17212 | November 1999 |
| Lennox | 6512 | December 1965 |
| Goodman | 5FU5472618P | June 2008 |
| Rheem | W291013412 | week 29 of 2010 |
| Rheem | 7351 M2806 16735 | week 28 of 2006 |
| Rheem | 0804B10488 | August 2004 |
| York | W0K5896070 | September 2005 |
Frequently asked questions
Can I find the age from the model number?
Usually not. The model number identifies the product line and size; the serial number carries the build date.
Why does the decoder ask for the brand?
Because the same character pattern encodes different things at different makers, for example Carrier (week-year) and Lennox (plant-year-month).