How old is my York furnace or AC?

By Dana Whitlock. Updated October 2026. Widely documented.

York's code hinges on character two. A digit there means October 2004 or later: that digit is the decade, character three is a month letter, and character four is the last digit of the year. W1E4677589 means a 2010s unit (1), built in May (E) of 2014 (4).

If character two is a letter, the unit predates October 2004. In that older style, character two is the month and character three is the year letter. The catch is that most year letters were reused every 21 years, so the same code can mean 1979 or 2000. The rules are Widely documented by inspectors and confirmed by a York recall notice, and resolving the old letter cycle usually takes one extra clue from the plate.

Where to find the label on a York furnace

York furnaces keep the rating plate inside the cabinet behind the blower access door; the CPSC's 2001 York furnace recall notice says the brand, model and serial are inside the removable front panels. Set the thermostat to off and shut off the furnace's service switch before you lift the panel, and read the plate with a flashlight from outside the cabinet. For York outdoor air conditioners and heat pumps, check the cabinet side panel near the service valves. Do not open the electrical access cover. That is a job for a licensed HVAC technician.

How to read the code

Newer format (October 2004 on): plant letter, decade digit, month letter, year digit, then six digits. The decade digit is 0 for the 2000s, 1 for the 2010s and 2 for the 2020s. W0K5 decodes as September 2005 and W1M0 as November 2010. Older format (1971 to September 2004): plant letter, month letter, year letter, a product letter, then six digits. WFKM is June (F) of 2001 (K). Both formats share the month letters: A through H are January through August, I and J are skipped, then K is September, L October, M November and N December. A leading code in parentheses such as (S) is ignored.

Real serials in this code

When the format changed

The old year letters skip I, O, Q, U and Z. A through N each cover two years 21 years apart: A is 1971 or 1992, J is 1979 or 2000, K is 1980 or 2001, N is 1983 or the first nine months of 2004. P through Y are single years, 1984 through 1991, so those need no guessing. To pick between the two possible years, look at the plate: a printed date settles it, as does an install invoice or permit. The refrigerant and efficiency rating help too, and a furnace that would be over 45 years old under the early reading rarely still runs. The 2001 CPSC recall, covering York furnaces made May to July 2001 with serials starting WFKM and WGKM, confirms the month-then-year order and the K-for-2001 reading.

Who makes York

York residential equipment was built by Johnson Controls and, before that, York International. The 2001 CPSC recall listed York, Luxaire and Coleman furnaces together, and those three brands share the York serial formats. In 2025 Bosch bought Johnson Controls' residential and light commercial HVAC business, including a long-term license to the York name, and York's warranty pages now sit on a Bosch site. York is sold through independent dealers.

How sure is this?

Widely documented. York doesn't publish this code; it comes from recall notices, service literature and inspector references. We tested the jci york rules against 35 serials, 8 of them with a date known from a recall notice, a printed label date or the maker. None decoded to a wrong year; codes whose year mark repeats show every possible reading. Always confirm with York's warranty page before you spend money on the answer.

Quick notes

• Character two tells you the era: a digit means October 2004 or later, a letter means earlier.
• Month letters skip I and J, so K is September and L is October.
• For an old-format serial with a year letter from A to N, use the printed date or install papers to pick the right decade.
• Luxaire and Coleman units decode the same way as York.
• Keep the model number with the serial; York's warranty and registration page asks for both.