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How old is my Lennox packaged unit?

Serial number age decoder for Lennox packaged rooftop and ground units: 1 format era, the decode rule in plain English, transcribed tables, and the official lookup.

Serial number decoder for Lennox packaged unit

Serial no.

Type the serial from the data plate, not the model number. Nothing is sent anywhere; the tables are in this page.

Format example: 5899L17212

Lennox packaged unit 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.
Lennox's official lookup at lennox.com returns Your Product's Coverage.

Format eras

1973 to present VERIFIED
####A#####digits 3-4 (YY)

How to read the serial

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

Month code	Month
A	January
B	February
C	March
D	April
E	May
F	June
G	July
H	August
J	September
K	October
L	November
M	December

Example: serial 5899L17212 decodes to November 1999.

Trap: Looks identical to Carrier style 1 (WWYY L #####). Century ambiguous (99=1999 vs 2099 not an issue, but 06=1906/2006 needs era). Lennox official lookup accepts formats ####A#####, A##A######, AA##A##### which implies newer alpha-prefixed formats NOT covered by building-center; treat those as low-confidence until sourced.

Where the data plate is on a packaged unit

On the cabinet exterior near the electrical access panel, or inside the panel door.

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

Official lookup: the authority

Open the official Lennox lookup takes serial (####A#####, A##A######, AA##A#####); returns Your Product's Coverage; URL verified live

This site is a reference built from published tables. The manufacturer's own lookup wins whenever the two disagree.

Sources

Frequently asked questions

How do I tell the age of a Lennox packaged unit from the serial number?

In the 1973 to present format the year is digits 3-4 (YY) and the month as letter at position 5 (A=Jan .. M=Dec, I skipped). Example: serial 5899L17212 decodes to November 1999.

Where is the serial number on a Lennox packaged unit?

On the data plate. On the cabinet exterior near the electrical access panel, or inside the panel door.