Every effort is undertaken to offer you correct and concise information to assist you in determining the age or manufacture date of HVAC equipment. Anytime anyone is dealing with numbers and letters in determining data, mistakes and misinterpretation are bound to happen. For this reason if you find during your research that we may have erred please contact us. In addition perhaps you have come across a brand, model or serial number format that we have not addressed. Email us information or pictures of data/nomenclature plates of the unit and we will attempt to assist you in your determinations. Email
This page was last updated: 26 July 2009.
Armstrong (1974 - Present)
Date of Manufacture (1974 to Present): The manufacturing date code is the third, fourth, and fifth digits of the serial number, and represents the year and month of manufacture. (To determine month: A = Jan; B = Feb; C = Mar; D = Apr; E = May; F = Jun; G = Jul; H = Aug; I was not used; J = Sep; K = Oct; L = Nov; and M = Dec.)
For example: 5899A05231 indicate that this sample Armstrong unit was manufactured in January of 1999.
Year of manufacture: 5899A05231
Month of manufacture: 5899A05231
Armstrong (Before 1974)
Date of Manufacture (Before 1974): The manufacturing date code is the first, second, and third digits of the serial number, and represents the year and month of manufacture.
For Example: 743xxxx indicate that this sample Armstrong unit was manufactured in March of 1974.
Year of manufacture: 743xxxx
Month of manufacture: 743xxxx
Other reported Serial Number Formats that are in need of clarification:
Armstrong Oil Fired Furnace - Serial # A26682BNA.
The Home Inspector declared that the last three letters of this serial number A26682BNA will tell you the month of manufacture, year of manufacture, and place of manufacture. The first of the three letters "B" (February) is the month; The second of the three letters "N" is the year (1992); and the last letter "A" is the location where it was manufactured. Please if anyone has any information for Armstrong Serial Numbers of this type email us. A picture of the nomenclature/data sticker or plate would be very useful.