How old is my Armstrong Air heat pump?

Serial number age decoder for Armstrong Air heat pumps: 2 format eras, the decode rule in plain English, transcribed tables, and the official lookup.

• Armstrong Air heat pump serial numbers in the 1973 to present format encode the year as digits 3-4 (YY) and the month as letter at position 5 (A=Jan .. M=Dec, I skipped) (source: building-center.org).
• Example: serial 5899L17212 decodes to November 1999.
• Armstrong Air heat pump serial numbers in the 1978 to 1992 format encode the year as char 8 via table (table below) and the month as char 7 (A=Jan .. M=Dec, I skipped) (table below) (source: building-center.org).
• Example: serial A14019ELA decodes to May 1990.
• Armstrong Air's official lookup at armstrongair.com returns warranty / registration lookup.

Format eras

• 1978 to 1992 VERIFIED
  A#####AAAchar 8 via table: 8=1978 9=1979 A=1980 B=1981 C=1982 D=1983 E=1984 F=1985 G=1986 H=1987 J=
• 1973 to present VERIFIED
  ####A#####digits 3-4 (YY)

How to read the serial

1978 to 1992 formatVERIFIED

Shape A#####AAA · example A14019ELA · confidence high

Year

char 8 via table: 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

Week or month

month = char 7 (A=Jan .. M=Dec, I skipped): A14019ELA = May 1990; A25175KKA = Oct 1989; C89274AAC = Jan 1980

Plant

char 9: A=Armstrong, B=Bellevue OH, C=Columbus OH

Example: serial A14019ELA decodes to May 1990.

1973 to present formatVERIFIED

Shape ####A##### · example 5899L17212 · confidence high

Year

digits 3-4 (YY)

Week or month

month = letter at position 5 (A=Jan .. M=Dec, I skipped)

Plant

digits 1-2 = factory/plant code

Example: serial 5899L17212 decodes to November 1999.

Listed under Lennox in the source; Armstrong Air is named in that format's family and the corporate link is an estimate, not a checked fact.

Where the data plate is on a heat pump

On the outdoor unit, same place as a condenser: a plate on the side or back of the cabinet near the line set. The indoor air handler carries its own plate with its own serial.

General guidance, not brand-specific: the owner's manual or the installer can point to the exact spot. See the data plate guide.

For scale only: the InterNACHI Standard Estimated Life Expectancy Chart for Homes lists Heat Pump at 10 to 15 years of expected service (nachi.org). That chart is a guideline, not a prediction for your unit.

What we could not confirm

• Armstrong Air is treated as sharing Lennox's format because the source lists it in that family; the corporate relationship itself is an estimate.
• Armstrong Air Conditioning Inc. is part of the Allied Air division of Lennox (building-center + site footer). Styles 4607B20058 (Lennox PPYYM) and A14019ELA / A25175KKA (1978-92 month-letter/year-letter/plant). armstrongair.com/resources/faqs/warranty/ exists. Allied serial lookup: https://apps.alliedconnect.com/WarrantyPeriodLookup/ExtendedWarrantyLookup.aspx?Alias=ALD&USERSORG=AR01

Sources

• https://www.building-center.org/lennox/
• https://www.lennox.com/residential/owners/assistance/warranty/official
• https://www.building-center.org/armstrong-air-hvac-age/
• https://www.building-center.org/wp-content/uploads/2017/09/ARMSTRONGAIR2-HVAC-Age.png
• https://www.building-center.org/armstrong-hvac-age/
• https://www.building-center.org/airease-hvac-age/
• https://www.building-center.org/wp-content/uploads/2015/09/Style-2_Airease-Date-of-Manufacture_Serial-Number-Nomenclature.png
• https://www.building-center.org/magic-pak-hvac-age/
• https://www.armstrongair.com/owners/warranty-registration/official

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