How to Determine the Month and Year of Manufacture on a Lennox A/C Unit

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You may remember when you purchased your Lennox air conditioner, but chances are you never thought you'd need to know precisely when it was made or how to find out. Determining the month and year of manufacture for a Lennox air conditioning unit is easy. It's included on the product label as part of the serial number, so you just need to know where to find the serial number and how to break the Lennox code.


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About Serial Numbers

In the manufacturing of many types of products, each unit coming off a production line is given a sequential, identifying serial number that distinguishes it from all other units produced.

A serial number is important to the manufacturer. It helps with tracking the history of a produced unit all the way through to the sale, and because the number can represent information about countless product specifications, including size, color, and weight, it can reveal what's selling and what isn't. Shipping errors are reduced through use of serial numbers, and in highly regulated industries, serial numbers help with compliance.


The use of serial numbers on electronics, automobiles, and appliances — all of which involve heavy demand for support — helps manufacturers provide better service to their customers. Warranty claims, for example, are tracked via serial number, and being able to provide a serial number allows a customer or repair technician to find the correct part needed when the product is in need of repair or some sort of replacement.

Locating Your Lennox Serial Number

The serial number for your Lennox air conditioner is printed in black on a white background on the data plate, or nameplate, which is found on the unit's exterior near the service panel. Lennox air conditioner serial numbers are composed of 10 characters that follow a specific pattern. That pattern is four digits, one letter, and five more digits.


Using 5621M 99989 as an example, the first two digits (56) indicate which of Lennox's several manufacturing facilities produced the unit. The third and fourth digits (21) are the year in which the unit was made — in this case, 2021. The fifth character is a letter representing the month of manufacture, which here is December. The list of letters Lennox uses to represent months excludes the letter "I" and runs as follows:

  • A


  • B


  • C


  • D


  • E


  • F


  • G


  • H


  • J


  • K


  • L


  • M



The final five digits in the Lennox serial numbering system stand for the unit's production sequence serial number.

Keeping a File

Air conditioning units aren't the only products you'll buy in your lifetime whose information you'll need from time to time. Product labels can fade, get wet, or become torn, possibly obliterating serial numbers, model numbers, and dates. Consider keeping a file of all product information so it will be at your fingertips the next time you need it.


Get into the habit of recording information for your file just after making purchases and also go through your house to take stock of everything you already own before labels can suffer damage. Photograph all labels to store in a digital file or simply record them in a notebook, rotary card file, or index-card file box. Be sure to include the purchase dates and manufacturer or dealer contact numbers.



Indiana University graduate, writer and DIY enthusiast Kynnie Kerry creates and markets high-end home softgoods and painted furniture treatments and has hands-on experience with home maintenance and remodeling projects — floor to ceiling — concept to completion.