Ten characters: four digits, a month letter A to M (skipping I), then five digits.
Lennox serial number lookup
Enter your Lennox equipment's complete serial to estimate its manufacture month, year and age. This lookup supports four digits, a month letter and five more digits.
Other documented Lennox serial shapes require a different rule and are not auto-decoded here.
Lennox serial formats and examples
The first two digits are a location prefix. Digits 3 and 4 identify the year; character 5 is the month letter. The remaining five digits identify the unit.
Does your serial match the supported format?
| Serial or label | What this tool supports | Your next step |
|---|---|---|
| Four digits, one month letter, five digits: PPYYMNNNNN | Supported for month letters A to M, skipping I, with a plausible date. | Enter all ten characters. Do not drop the location prefix. |
| Letter-prefixed, shorter or longer serial | No automatic date from this lookup. | Lennox's official lookup accepts other serial shapes. Verify the full number there. |
| Other product-specific or legacy code | This table does not establish a date. | Supply the model and serial together so Lennox can identify the product and format. |
Worked date-code examples
These examples illustrate the format. They are not records for your equipment.
5809C05716March 2009
58 is the location prefix, 09 is the year and C is March. The year is not in the first two positions.
5810A12345January 2010
10 is the year and A is January. The last five digits do not identify the month.
5809I05716No date: I is not a month code
The fifth character is I, which the manufacturer key skips. The tool asks you to check the label and does not reinterpret the failed modern format as a legacy date.
5809C057160Verify the longer sequence
Lennox service literature allows some six-digit sequences, but this lookup supports the stated ten-character shape. Use Lennox's official lookup for this illustrative eleven-character number. An unsupported result does not mean your equipment serial is invalid.
How the full year is established
Digits 3 and 4 give two year digits. Ordinary supported results use a 2000s interpretation. For an older example such as 5896A36571, confirm 1996 from the equipment label or manufacturer record before relying on January 1996. Without century evidence the tool returns no date, rather than assuming an age.
A serial-format match is an estimate. It does not establish installation date, warranty coverage, equipment condition or remaining life.
Month letters used by this lookup
Read character 5 only after confirming the full serial shape. The letter I is skipped.
- A
- January
- B
- February
- C
- March
- D
- April
- E
- May
- F
- June
- G
- July
- H
- August
- J
- September
- K
- October
- L
- November
- M
- December
If the number does not match
- Check the row marked Serial or S/N. The model number describes a product, rather than its manufacture date.
- Copy every character, including leading zeros. Spaces and dashes can stay; do not add or rearrange digits to make a match.
- Use the equipment rating plate, rather than the label on a replacement board or compressor. Ask a technician for a label photo if access requires removing a service panel.
- Keep the model and serial together and verify with Lennox.
Lennox age lookup questions
Which digits give the year in a Lennox serial?
For the supported four-digit, month-letter, five-digit shape, digits 3 and 4 give the two-digit year. The first two are a location prefix. Other serial shapes need their own manufacturer reference.
What does the fifth letter mean?
This lookup reads A through H as January through August, then J, K, L and M as September through December. I is skipped. This key applies only to the serial shape stated above, not to every Lennox-branded product.
Why does the official lookup accept a number this tool does not?
Lennox lists multiple serial shapes, including letter-prefixed versions. This tool only decodes its stated ten-character format. An unsupported result is a request for verification, not evidence that your serial or equipment is invalid.
Can I use a Lennox mini-split or replacement-part serial here?
Only if its equipment serial matches the stated format and the product's documentation confirms that rule. Different product lines and components may use different codes. Use Lennox's official lookup or support when the format differs.
References and verification
Date-code references checked October 5 and 6, 2026; year-handling reviewed October 7. These documents explain particular formats; they do not confirm your unit's record.
- Lennox model and serial nomenclature
The serial-numbering diagram identifies the year and month positions and the complete month-letter key, including the skipped I. Product-specific formats still need their own documentation.
- Lennox serial identification example
SL18XC1 service literature labels the location, year and month positions, with 5809C05716 and A/B/C month examples. It also documents sequence lengths beyond this tool's scope.
- Lennox official serial-format help
The warranty lookup lists several accepted serial shapes. A format match in this tool does not confirm a manufacturer record or warranty coverage.