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Official Lennox warranty & serial services

Read the plate. Check the evidence.

Lennox Serial Number Lookup: Furnace & AC Age

Verified legacy 1978 example and current plant-year-month-letter nomenclature.

Browse Lennox manuals and guides →

Check a documented system

What’s on the rating plate?

Lennox unitary HVAC; specialized/imported product families may differ.

Spaces and dashes are accepted. Check O/0 and I/1, and keep any leading zeros.

Checks ENERGY STAR model records and searches manuals separately from the serial. Certification records do not establish this unit’s manufacture date.

Known product context (optional)

Choose a system only when it matches the product family and its documentation. A purchase year or a manual’s publication date does not establish a manufacturing date.

Explore a sourced example:

Scope matters

Supported formats
and historical limits.

  • Manufacture date is distinct from installation, purchase and warranty start dates.
  • The date code does not identify a full model, capacity or configuration. Enter the separate model from the rating plate for manual search.
  • Often-quoted1973/74 start and pre-1973 numeric formats were not confirmed by the primary documents reviewed.
  • The initial two digits are plant/division, not manufacture year.

Research reviewed October 16, 2026. This independent tool applies published rules and retains unresolved years and model candidates.

Source references

Lennox: plant, year and month letter

hvac

Manufacturer legacy diagram gives 5178M99989 (December1978); current manufacturer guide confirms 58 21 C 05716 and five/six sequence digits. No primary source establishing the often-repeated 1973/74 changeover was found, so earlier codes are held for review. Code55 identifies Heatcraft division; the plant location is not established.

Reading your result

Lennox lookup questions

Why does the year code match more than one year?

Some systems reuse letters or only encode the last one or two year digits. Every supported interpretation is retained. A decade supplied from reliable records can narrow the reading; the tool does not automatically pick the newest year.

Does the serial identify my exact model?

Usually the model is a separate plate field. Where published serial ranges actually identify a model, the result shows model candidates and links to their manuals. Overlapping ranges remain ambiguous.

Can I share the result?

After a lookup, the address includes the serial in a fragment beginning with #serial=. Use “Copy share link” to share the serial and selected context. Opening the link runs the same lookup. The fragment is not a query-string result page.