How to find the age of a furnace or AC unit
Every furnace, air conditioner and heat pump has a rating plate with a model number and a serial number. On outdoor units it’s on the cabinet; on furnaces and air handlers it’s usually inside the access panel or blower door. Turn off power to a furnace before removing a panel. Copy the serial number and pick the brand printed on the plate.
The decoder gives the manufacture date, which is not the install date. Equipment is often installed months after it was built. Some newer plates print the manufacture date directly; if yours does, use it.
How each brand writes the date
| Brand | Date code | Example |
|---|---|---|
| Goodman | Digits 1–2 = year, 3–4 = month [1][2][3] | 9704811080: April 1997 |
| Lennox | Digits 3–4 = year, then a month letter [4][5] | 5898G07568: July 1998 |
| Carrier / Bryant | Digits 1–2 = week, 3–4 = year [7][8] | 4006A17330: week 40 of 2006 |
| Trane / American Standard | Four styles by era; since 2010 the year + week come first [9][10] | 130313596L: week 3 of 2013 |
| York / Luxaire / Coleman | Since Oct 2004: the year is split around a month letter. Before: letters [11][12] | W0K5896070: September 2005 |
Why the brand matters
Serials that look identical can mean different things. A Lennox serial and a Carrier serial both have four digits, a letter and five digits, but Lennox puts the year in digits 3–4 and the month in the letter, while Carrier puts the week in digits 1–2 and the year in 3–4. 5205J24862 is September 2005 as a Lennox but week 52 of 2005 as a Carrier.
When a serial gives two years
York used letters for the year until 2004, repeating every 21 years, so an older York serial usually has two possible years [11][12]. And for two Trane year letters, S and Z, the published charts disagree [9][10]. In both cases the decoder shows every candidate and says which source gives which, rather than picking one.
What this decoder doesn’t cover
- Brands outside the five above, such as Rheem/Ruud HVAC, Amana, Heil/ICP and Nordyne.
- Older styles where sources disagree: Lennox before 1973, Carrier before 1980, Trane 1980–82 and hyphenated 1970s serials, York’s pre-1980 two-letter codes, and Goodman PTAC units.
Common questions
How do I find out how old my furnace is?
Read the serial number on the rating plate inside the furnace’s access panel and decode it above with the brand on the plate.
How do I find the age of my AC unit?
The outdoor unit has its own rating plate on the cabinet. It can be a different age from the furnace or air handler indoors, so decode both.
Is the serial number date when my system was installed?
No, it’s when the unit was built. Installation records or permits give the install date.
Bryant, Payne, Day & Night, Luxaire, Coleman, American Standard: are they covered?
Yes. Bryant, Payne and Day & Night use Carrier’s code; Luxaire and Coleman use York’s; American Standard uses Trane’s. Pick the matching option in the brand list.
Brand pages
- Goodman furnace and AC age: Year + month in the first four digits, confirmed by a CPSC recall.
- Lennox furnace and AC age: Plant code, two-digit year, then a month letter.
- Carrier and Bryant furnace and AC age: Week + year in the first four digits (also Bryant, Payne, Day & Night).
- Trane and American Standard furnace and AC age: Four serial styles from the 1970s to today, including disputed year letters.
- York furnace and AC age: October 2004+ style and the older four-letter style with a 21-year cycle.
Not affiliated with any HVAC manufacturer. Brand names are used only to say which serials the decoder reads.
Sources
- Building Intelligence Center: Goodman HVAC AgeUsed for: Year + month first (10 digits).
- PickHVAC (Rene Langer, 2025-06-03): How old is my Goodman AC or furnace or heat pump?Used for: Year + month first (10 digits).
- U.S. Consumer Product Safety Commission: Goodman Recalls Air Handlers Due to Electrical Shock Hazard (recall 17-103, 2017-03-02)Used for: Year + month first (10 digits).
- Building Intelligence Center: Lennox HVAC AgeUsed for: Plant code + year + month letter (4 digits, letter, 5 digits).
- PickHVAC (Rene Langer, 2025-06-03): Lennox HVAC Age: Serial Number DecodingUsed for: Plant code + year + month letter (4 digits, letter, 5 digits).
- Honest Home Inspections, LLC (hosted by InspectAPedia): How to determine Water Heater and Furnace Age (PDF, last updated 2009-01-06)Used for: Plant code + year + month letter (4 digits, letter, 5 digits); Week + year first (4 digits, letter, 5 digits); 9 characters, one-digit year + week (2002–2009); 9 characters, year letter + week (1983–2001); Four letters + 6 digits (1971 – September 2004).
- Building Intelligence Center: Carrier HVAC AgeUsed for: Week + year first (4 digits, letter, 5 digits).
- PickHVAC: Carrier HVAC Age: Serial Number BreakdownUsed for: Week + year first (4 digits, letter, 5 digits).
- Building Intelligence Center: Trane HVAC AgeUsed for: 10 characters, year + week first (2010 on); 9 characters, one-digit year + week (2002–2009); 9 characters, year letter + week (1983–2001); Factory letter + year + month letter (1970s–1990s).
- PickHVAC (Rene Langer, 2025-06-03): Trane HVAC Age: Serial Number DecodingUsed for: 10 characters, year + week first (2010 on); 9 characters, one-digit year + week (2002–2009); 9 characters, year letter + week (1983–2001); Factory letter + year + month letter (1970s–1990s).
- InterNACHI forum: York A/C & Furnace Serial No Decoding Help (post by John Bowman, 2009-06-22)Used for: Letter, digit, month letter, digit (October 2004 on); Four letters + 6 digits (1971 – September 2004).
- PickHVAC (Rene Langer, 2025-06-03): York HVAC Age: Serial Number DecodingUsed for: Letter, digit, month letter, digit (October 2004 on); Four letters + 6 digits (1971 – September 2004).
- Building Intelligence Center: York HVAC AgeUsed for: Letter, digit, month letter, digit (October 2004 on); Four letters + 6 digits (1971 – September 2004).
- Inspector's Journal forum: York dates off in decoder chart (thread, 2008-08-12)Used for: Letter, digit, month letter, digit (October 2004 on).