Furnaces average 15-20 years of service life. Carrier and Goodman encode the year and week in the first four digits. Trane uses a year-week format embedded differently depending on the decade. Lennox uses a format where the 3rd and 4th digits equal the year.
The Importance of Furnace Age
Knowing your furnace's age is critical for efficiency upgrades and predicting heat exchanger failure. A unit past 15 years often costs more to repair than replace.
Carrier and Bryant Decoding
Carrier encodes the week and year in the first four digits of the serial number. The format is WWYY. So, 3218... means the 32nd week of 2018.
Trane and American Standard
Modern Trane units use the first two digits for the year and the next two for the week (YYWW). Older units may use a letter code for the year.
Lennox and Goodman
Goodman uses the first four digits as YYMM. Lennox typically uses the 3rd and 4th digits of the serial number for the year, and the 5th character (a letter) for the month.