The unit is a hydronic forced warm air unit. First letter do serial # is year. Branded but I guess they are their own company. Serial Number format: L943321238 (This serial number is from an actual furnace). Date of Manufacture: Using the second, third, fourth and fifth digits of the serial number L. 21238 you will find the year and week of manufacture. The second and third digits are the year of manufacture and the fourth and fifth digits are the week. Age: First two letters of the serial number indicate age, where the first letter is the month and the second letter the year of manufacture.

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