Home / Furnaces and AC units / Concord
How old is my Concord furnace or AC?
Type the serial number from the Concord label to see when it was built. Concord units are built by Allied Air, a Lennox company, so the serials follow that company's format.
Example
- 018329Running number, not part of the date
- 04Year: 04 = 2004
- 31Week: 31 (around August)
Built Week 31 of 2004 (around August)
22 years, 2 months old
In replacement window. Inside the usual 15 to 25 year lifespan, so replacement could come any time. Worth budgeting for it.
How this was read
- The serial is 10 digits with no letter. On this format the date is at the end.
- Digits 7 and 8, 04, are the year: 2004.
- The last two digits, 31, are the week of the year.
Format: All-digit serial with year and week at the end. Sources: InspectAPedia: how to determine furnace age, with Ducane’s explanation (PDF), InterNACHI forum: Armstrong furnace date code, Building Intelligence Center: Armstrong, Building Intelligence Center: Ducane, Inspector Handbook: Armstrong Air, Lennox model and serial nomenclature (PDF).
Reading a Concord serial number
Concord is an Allied Air brand. Some serials are all digits with the year and week at the end. Others use the Lennox layout.
About Concord
- Concord and Ducane shared one line of air conditioners and heat pumps, from 13 to 18 SEER, as of 2010.
- Concord is sold through independent wholesale distributors in the US and Canada, not through Lennox dealers.
Sources: Allied Air Impresses Distributors With New Heating, Cooling Products, Lennox International Inc. Form 10-K for 2024
Plant code, year and month letter
Used about 1974 to today. Example: 8499F63244
Armstrong Air, Ducane, AirEase and Concord use the Lennox layout: two plant digits, two year digits, then a month letter (A is January, I is skipped). 8499F means June 1999.
Worked example: 8499F63244 was built June 1999, so it is 27 years, 4 months old as of October 2026.
| Letter | Month |
|---|---|
| A | January |
| B | February |
| C | March |
| D | April |
| E | May |
| F | June |
| G | July |
| H | August |
| J | September |
| K | October |
| L | November |
| M | December |
Sources: InspectAPedia: how to determine furnace age, with Ducane’s explanation (PDF), InterNACHI forum: Armstrong furnace date code, Building Intelligence Center: Armstrong, Building Intelligence Center: Ducane, Inspector Handbook: Armstrong Air, Lennox model and serial nomenclature (PDF)
Armstrong month letter and year letter
Used 1978 to 1992. Example: A25175KKA
Older Armstrong serials end in three letters. The first is the month (A is January, I is skipped), the second is the year (8 is 1978, A is 1980, K is 1989), and the last is the plant. A25175KKA means October 1989.
Worked example: A25175KKA was built October 1989, so it is 37 years old as of October 2026.
| Letter | Month |
|---|---|
| A | January |
| B | February |
| C | March |
| D | April |
| E | May |
| F | June |
| G | July |
| H | August |
| J | September |
| K | October |
| L | November |
| M | December |
| Character | Year |
|---|---|
| 8 | 1978 |
| 9 | 1979 |
| A | 1980 |
| B | 1981 |
| C | 1982 |
| D | 1983 |
| E | 1984 |
| F | 1985 |
| G | 1986 |
| H | 1987 |
| J | 1988 |
| K | 1989 |
| L | 1990 |
| M | 1991 |
| N | 1992 |
Sources: InspectAPedia: how to determine furnace age, with Ducane’s explanation (PDF), InterNACHI forum: Armstrong furnace date code, Building Intelligence Center: Armstrong, Building Intelligence Center: Ducane, Inspector Handbook: Armstrong Air, Lennox model and serial nomenclature (PDF)
All-digit serial with year and week at the end
Used about 1990 to the 2000s. Example: 4140720328
Some Ducane, AirEase and Concord serials are 10 digits with no letter. The last four digits are the year (2 digits) and the week (2 digits). Ducane gives 9933 as the 33rd week of 1999.
Worked example: 0183290431 was built Week 31 of 2004 (around August), so it is 22 years, 2 months old as of October 2026.
Sources: InspectAPedia: how to determine furnace age, with Ducane’s explanation (PDF), InterNACHI forum: Armstrong furnace date code, Building Intelligence Center: Armstrong, Building Intelligence Center: Ducane, Inspector Handbook: Armstrong Air, Lennox model and serial nomenclature (PDF)