Armstrong Air serial number lookup: age of a furnace, AC or heat pump
The serial number is on the rating plate on the front or side of the unit. In an Armstrong Air serial from 1993 or later, the third and fourth digits are the year and the letter after them is the month.
Decode an Armstrong Air serial number
How to read an Armstrong Air serial number
Armstrong Air has used 2 serial formats. Find the one that matches the shape of your serial.
Plant code, year, month letter
The first two digits are the plant. The third and fourth digits are the year. The letter after them is the month, A for January through M for December with the letter I left out.
Shape: four digits, a letter and five digits.
1611A12345 reads as January 2011.
Month letter
- A January
- B February
- C March
- D April
- E May
- F June
- G July
- H August
- J September
- K October
- L November
- M December
Plant codes: 16 Orangeburg, 46 Blackville, 56 Stuttgart, 58 and 59 Marshalltown, 60 Grenada, 84 Bellevue, 17 and 19 Saltillo.
Month, year and factory in the last three characters
Read from the end. The last character is the factory. The character before it is the year and the one before that is the month, A for January through M for December with the letter I left out.
Shape: eight to ten characters ending in three letters, or two letters with a digit between them.
A25175KKA reads as October 1989.
Year code
- 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
Month letter
- A January
- B February
- C March
- D April
- E May
- F June
- G July
- H August
- J September
- K October
- L November
- M December
Factory letters: A Armstrong, B Bellevue, Ohio, C Columbus, Ohio.
Where to find the serial number
The model and serial numbers are on the rating plate on the front or the side of the unit.
If the serial number does not decode
- Armstrong Air equipment is built by Allied Air Enterprises, a Lennox International company.
- When the installation date cannot be verified, Allied Air counts warranty from 90 days after the manufacture date in the serial.
- Gas furnaces from the 1980s and 1990s print the year of the safety standard they were certified to, for example “Z21.47” followed by a year. The furnace was built in that year or a few years after it.
- Armstrong serials from before 1978 are not covered by the manufacturer’s guide and are not decoded here.
What the age tells you
| Equipment | Typical service life |
|---|---|
| Furnace | 15 to 22 years |
| Central air conditioner | 10 to 21 years |
| Heat pump | 15 to 16 years |
About Armstrong Air
Armstrong Furnace Company was set up by Lennox in Columbus, Ohio in 1928. Armstrong Air is now a brand of Allied Air Enterprises, a Lennox International company, with assembly in Orangeburg, South Carolina.
Brands that share this serial system: Ducane, Lennox.
Questions and answers
Which characters in an Armstrong Air serial number show the date?
The first two digits are the plant. The third and fourth digits are the year. The letter after them is the month, A for January through M for December with the letter I left out. This applies to units built since January 1993.
Why does my Armstrong Air serial number look different?
Armstrong Air has used 2 serial formats: plant code, year, month letter (built since January 1993); month, year and factory in the last three characters (built 1978 to 1992). The decoder tries each one.
Who makes Armstrong Air heating and cooling equipment?
Armstrong Air equipment is built by Allied Air Enterprises, a Lennox International company.
Sources
- Allied Air Enterprises: Warranty Procedures WP20595203, revision 10 (2015), serial number section (manufacturer): https://s7d2.scene7.com/is/content/AlliedAirEnterprises/Warranty%20Documents/Warranty%20Library_2015%20Warranty%20Procedures%20Rev%2010.pdf
- Building Intelligence Center: Armstrong Air HVAC age (independent reference): https://www.building-center.org/armstrong-hvac-age/
- Building Intelligence Center: Ducane HVAC age (independent reference): https://www.building-center.org/ducane-hvac-age/
- Allied Air Enterprises: warranty lookup (manufacturer): https://apps.alliedconnect.com/WarrantyPeriodLookup/ExtendedWarrantyLookup.aspx?Alias=ALD&USERSORG=AR01
Formats last checked against these sources on October 5, 2026. Found a serial that does not fit? Send a correction. How formats are verified: method and sources.