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Lennox furnace and AC age

How old is my Lennox furnace or air conditioner?

A Lennox serial number shows the year and month the unit was made. Enter yours to decode it with Lennox’s published numbering system.

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Decode your serial number

Your serial number stays in your browser. It isn’t sent to us or stored unless you choose to save it to your home.

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Photo reading needs a free account and your permission to use an external AI service. It reads the text only; the date is always worked out from the manufacturer rule.

How the date code works

  1. Digits 1–2: division. The factory that built it.
  2. Digits 3–4: year.
  3. The letter: month. A is January through M for December, with no I.
  4. The last digits are the unit’s own serial.

Lennox’s example 5178M 99989 is division 51, December 1978. Lennox used a different style before 1973, so we read year codes as 1973–1999 or 2000 onward. The same code covers Lennox furnaces, air conditioners and heat pumps.

Source: Lennox — Model and Serial Nomenclature (Serial Numbering System). Aruvello is not affiliated with Lennox.

Where to find the serial number

On a furnace, the rating plate is inside the cabinet near the burner area. On outdoor units it’s mounted on the outside of the cabinet. The serial number is printed beside the model number.

Age, installation and warranty

This is the date the unit was made. It may have been installed later. Lennox warranty depends on the model, registration and installation date, and only Lennox or your dealer can confirm it. Aruvello doesn’t determine coverage.

Other brands: see which brands we support.

Questions homeowners ask

Can this be confused with a Carrier serial?
Yes. Both start with four digits and a letter, but Lennox puts the year in digits 3–4 and the month in the letter. Pick the brand on your label.
Does this cover Armstrong Air, Ducane or AirEase?
No. We’ve only checked Lennox-branded labels against this document.
Should I replace an old system?
Age alone can’t tell you. Ask a licensed HVAC technician to inspect it.

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