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Lennox family

How old is my Armstrong Air furnace?

Enter the serial number from the label. The date comes from Armstrong Air's documented serial rules, not a guess.

Look for “Serial No.” or “S/N” on the label. Spaces and dashes are fine.

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How to read a Armstrong Air furnace serial number

Armstrong Air is an Allied Air brand, and Allied Air describes itself as “A Lennox International, Inc. Company”. Allied’s official warranty procedures document is the main source for Armstrong Air dates. Units made since January 1993 use the Lennox layout (plant, two-digit year, month letter), and units from 1978 to 1992 use an older Allied letter format that we also decode.

  • Plant + year + month letter (Lennox since the 1970s; Allied brands since 1993)

    Example: 1611A12345 (Armstrong Air) was made in January 2011. Lennox-family serials start with a two-digit plant code (16), then the year (2011) and a month letter ("A" = January; the letter I is skipped, so J is September).

  • Allied letter format (Armstrong Air / AirEase, 1978–1992)

    Example: C89274AAC (Armstrong Air) was made in January 1980. On Armstrong Air and AirEase units built 1978–1992, the 7th character is the month ("A" = January) and the 8th is the year ("A" = 1980).

Not decoded yet: Older all-numeric Ducane/Concord serials, pre-1973 Lennox and 1970s AirEase formats, and Lennox ductless units are not decoded yet.

Where to find the serial number

Turn the furnace off at its switch, then remove the upper access door (the burner or blower compartment). The rating plate is on the inside wall of the cabinet or on the back of the door.

The plate lists the model number and serial number; many newer plates also print a date of manufacture.

How long does a furnace last?

A typical furnace lasts about 15–20 years. That's a general estimate: maintenance, usage, climate and installation all matter, and age alone doesn't tell you a unit's condition.

Range from NAHB / Bank of America, Study of Life Expectancy of Home Components (2007, archived copy), Carrier: how long does a furnace last? and Lennox: how long does a furnace last?.

Armstrong Air furnace recalls

From the U.S. Consumer Product Safety Commission, checked 2026-09-29. A decoded result checks your model number against recalls live.

Questions

How do I read a 1978–1992 Armstrong Air serial?
These serials are nine characters. The 7th is the month letter. The 8th is the year: 8 or 9 for 1978–79, then A to N, skipping I. The 9th is the factory, where Allied lists A as Armstrong, B as Bellevue, Ohio, and C as Columbus, Ohio. On a real Armstrong Air plate, A14019ELA reads E for May and L for 1990.
Does a model number starting with A7 mean Armstrong Air?
It means Armstrong Air or AirEase. Allied’s spec sheets read “Brand A = AirEase | Armstrong Air”, and both brand sites list the same A7AC and A7HP models. Either way, the serial rules are the same.
How can I tell how old my Armstrong Air furnace is?
Find the serial number on the rating plate and enter it above. Armstrong Air furnaces use the Lennox family serial format, which includes the manufacture date. For example, 1611A12345 was made in January 2011: Lennox-family serials start with a two-digit plant code (16), then the year (2011) and a month letter ("A" = January; the letter I is skipped, so J is September).
Where is the serial number on a Armstrong Air furnace?
Turn the furnace off at its switch, then remove the upper access door (the burner or blower compartment). The rating plate is on the inside wall of the cabinet or on the back of the door. The plate lists the model number and serial number; many newer plates also print a date of manufacture.
How long does a furnace usually last?
A typical service life is about 15–20 years. That's a general estimate: maintenance, usage, climate and installation all matter, and age alone doesn't tell you a unit's condition.
Do Lennox, Ducane, AirEase and Concord furnaces use the same serial format?
Yes. Armstrong Air, Lennox, Ducane, AirEase and Concord use the same serial-number conventions (Lennox family), so the same decoding rules apply.
How reliable is the result?
The Lennox family rules come from documented sources, but they're in Beta while we check more real-world examples, so results are capped at medium confidence. If a serial doesn't match a documented format, we say so instead of guessing.

Same serial format: Lennox furnace, Ducane furnace, AirEase furnace, Concord furnace

Other Armstrong Air equipment: air conditioner, heat pump

Sources

Rules last reviewed 2026-09-28. These rules are in Beta while we verify more real-world examples, so results are capped at medium confidence.

Manufacture dates are decoded from manufacturer serial-number conventions and available documentation. Serial formats can change. Verify critical equipment information with the manufacturer when necessary.