Lennox HVAC Age: Serial Number Decoding for AC, Furnace & Heat Pump

How old is my Lennox? How can I tell using the serial number?

Answer: For most Lennox equipment, the third and fourth characters of the serial number are numbers, and they indicate the year. For example, 94 is 1994 and 08 is 2008.

The fifth character is a letter that corresponds to a month – A is January, for example. The month key code is found below.

How to Read a Lennox Serial Number

This Lennox serial number lookup works for the Lennox age of unit lookup on air conditioners, heat pumps, gas furnaces, air handlers, boilers and mini split ductless heat pumps.

In total, Lennox has used 4 different styles of serial numbers on their furnaces, boilers, heat pumps, air handlers, AC units, and mini-splits.

These serial numbers date back to the 1960’s but the current style has been used since 1974 on all Lennox HVAC equipment making serial number lookup and easy task.

These aren’t model numbers: This post is about Lennox serial numbers, not Lennox model numbers that have nomenclature related to series, capacity, and performance of Lennox HVAC equipment.

Where is the Lennox Serial Number?

You can find the serial number on the rating or data plate, sometimes called a rating or data tag.

On a Lennox furnace, you will find the rating plate by removing the top, front, service panel. The rating plate is often placed on the left side of the cabinet, although the type of furnace you have may impact the exact placement.

On a Lennox boiler you can find the rating plate on the exterior at the top of the unit.

On Lennox air conditioners, heat pumps and mini-splits, look for the rating plate on the exterior of the unit near the service panel.

These information tags are hard to miss. They contain the serial number, which might be written “Serial #” or “S/N,” and they contain other specs like voltage. The model number is on the tag too.

How to Read a Lennox Serial Number – Details

In each of these examples, the characters that indicate the manufacture date have been underlined. The other numbers and letters identify the plant where the unit was made and the sequence of manufacture.

Style #1: 10 Characters – Numbers and One Letter – 1974 to Present

Style # 1 is the most common style and always begins with 4 numbers, followed by one letter, and ends with 5 more numbers.

The first 2 numbers usually indicate the factory where the unit was made and are not used in decoding the manufacture date.

Example serial number: 5205J24862

Year: the 3rd and 4th numbers indicate the manufacture year, here 05, so the year is 2005.

Month: The 5th character, which is a letter, indicates the month the unit was made based on the Lennox Month of Manufacture code below. In this case the letter is J so the unit was made in September.

Manufacture Date: September 2004

This image shows this serial number type.

The unit was produced in August 2019.

Style # 2: 9 Characters – Letters & Numbers – Late 1970s to Early 1990s

Style # 2 begins with a letter, followed by 5 numbers, and ends with 3 letters. This style was primarily used in the late 1970s through the early 1990s.

Example Serial #: C86185EDC

Year: The 2nd and 3rd characters are numbers and indicate the year the unit was made. These numbers are 86, so the unit was made in 1986.

Month: The second to last character is a letter indicating  the month of manufacture, here the letter is “D”, so the unit was made in April. See the Lennox Month of Manufacture code below.

Manufacture Date: April 1986

Style #3: 10 Characters – Numbers and Letters – 1960s and 1970s

Style # 3 begins with 2 numbers, then a letter, then 2 more numbers, followed by 2 more letters, and three more numbers. This style was in the 1960’s and 1970’s.

Example Serial #:  09B56JK590

Day: The 1st and 2nd characters represent the day of the month the unit was made. In this case the numbers are 09, so the 9th day of the month.

Month: The 3rd character is a letter and indicates the month the unit was made. The letter is a “B”, so the unit was made in February, based on the Lennox Month of Manufacture code below.

Year: The 4th and 5th characters indicate the year, in reverse, that the unit was made. These numbers in the example are “56”, so the unit was made in 1965.

Manufacture Date: February 9, 1965

Lennox Code for Month of Manufacture

A = January                   G = July

B = February                 H = August

C = March                     J = September

D = April                        K = October

E = May                         L = November

F = June                        M = December

Note that the letter “I” is not used – probably because it could be confused with the number 1.

Style # 4: 10 Characters – All Numbers

Style # 4 uses all numbers. The 7th and 8th numbers indicate the year that the unit was made and the 9th and 10th numbers represent the week of the year the unit was made.

Example Serial #:  4592711225

Year: The 7th and 8th numbers are 12, so the year is 2012

Month: The 9th and 10th numbers are 25, so the 25th week of the year will fall in June.

Manufacture Date: June 2012

Interested in Replacing Your Lennox HVAC Unit?

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Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree from Lone Star College and EPA & R-410A Certifications.

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