How Old Is My Lennox Air Conditioner or Furnace?

Your Lennox unit's age is encoded in its serial number. Here is exactly how to decode it or use our free tool.

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Where to find the Lennox serial number

On an air conditioner or heat pump, look for the data plate on the side or rear of the outdoor unit. On a furnace, open the upper front door — the plate is inside the cabinet.

How to decode a Lennox serial number

Format: Plant+Year+Month letter (PPYYL)

Digits 1–2 = plant code (not the date).
Digits 3–4 = year.
5th character = month letter: A=Jan through L=Dec.

Worked example: 5805L12345 = December 2005, plant 58

Lennox month letter (5th char)
A=Jan	B=Feb	C=Mar	D=Apr	E=May	F=Jun
G=Jul	H=Aug	I=Sep	J=Oct	K=Nov	L=Dec

Lennox also usually prints the exact date on the data plate.

What your unit's age means

Typical lifespan for residential HVAC is 15–20 years. Under 10 years: repair with an OEM part. 10–15 years: repairs usually still win. Past 15 years: compare repair vs replacement.

R-22 warning: if your Lennox AC or heat pump was manufactured before 2010, it likely runs phased-out R-22 refrigerant.

Frequently asked questions

My Lennox serial number does not match this format

You may have an older unit or be reading the model number. Email a photo of your data plate to info@nationalhvacparts.com and we will decode it free.

Should I repair or replace my Lennox unit?

A DIY OEM part repair costs $30–$250, a technician $200–$700, replacement $6,000–$12,000+. Unless the compressor or heat exchanger has failed on a 15+ year unit, repair wins. Start with our diagnostic guide.

Need HVAC parts?
We stock 15,000+ OEM Carrier, Bryant, Payne and ICP parts. Find parts by model number.

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How Old Is My Lennox Air Conditioner or Furnace?

Where to find the Lennox serial number

How to decode a Lennox serial number

What your unit's age means

Frequently asked questions