The “prefix” serial numbers you mentioned on Armstrong flutes are 2 digits, a dash, plus 5 more digits. For example: Serial# 24-58637 = 24 + 50 = 1974. In your case, the serial number is 7 digits with no prefix.Click to see full answer. Simply so, how do I read my Armstrong Air serial number? How do I tell the age of an Armstrong Air furnace or air conditioner from the serial number? The 8th digit of the serial number, which will be a letter (and typically the next to last digit) denotes the year of manufacture for units manufactured from the 1980s to the early 1990s: A = 1980 I = (not used) Similarly, how long does a furnace last? 15 years One may also ask, how do you read a Heil model number? Look for the line that states “Model Number” or “M/N”. The number after will be the model number of your Heil furnace. Use this number for locating replacement parts or referring to the model of your furnace.How do I find out how old my furnace is?Pull off the removable door on the outside of your furnace; this is usually along the bottom of the front of the unit. Look at the interior of the metal door for a label or tag listing the furnace’s serial number. This may also show an actual manufacturer’s date, depending on the company that made the furnace.
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