Lennox Serial Number: How Old Is My Lennox Furnace or AC?
Characters 3 and 4 of a Lennox serial number are the year and character 5 is a letter for the month. Type the serial number below for the exact month and year.
About Lennox
Lennox has built furnaces in Iowa since 1895 and now makes furnaces, air conditioners and heat pumps under the Lennox name. Its serial code has stayed the same since 1974, which makes it one of the easiest to read.
By type: Lennox furnace age · Lennox air conditioner age
Where to find the serial number
Furnace: Take off the front lower panel (turn the power off first). The data plate is a metal or foil sticker on the inside of the door or on the side of the cabinet, next to the blower. The serial number is usually labelled "Serial No.", "S/N" or "Ser. No."
Air conditioner: On the outdoor unit (the condenser), look for the data plate on the side panel, often near the electrical box where the power cables go in. The indoor coil or air handler has its own plate with a different serial number.
How to read a Lennox serial number
Characters 3 and 4 of a Lennox serial number are the year and character 5 is a letter for the month.
10 characters, 1974 to today
PP YY M #####
- Characters 1 and 2 are the factory.
- Characters 3 and 4 are the year: 98 means 1998, 10 means 2010.
- Character 5 is the month as a letter.
Example: 5898F06044
Month letters: A = January, B = February, C = March, D = April, E = May, F = June, G = July, H = August, J = September, K = October, L = November, M = December (there is no I).
Units made before 1974 use an older code that we do not decode yet.
How long does a furnace last?
Most furnaces last 15 to 20 years. Yearly servicing, the local climate and how hard it works all move it within that range. Past 15 years, it is worth getting a replacement price before the unit fails, so you aren't forced into a rushed decision.
Questions
How do I tell how old my Lennox furnace is?
Find the serial number on the data plate and read it with the Lennox code: Characters 3 and 4 of a Lennox serial number are the year and character 5 is a letter for the month. Or type it into the decoder on this page.
Is the manufacture date printed on the label?
Often, yes, especially on newer units and water heaters. Look for "Mfg. date", "MFD" or "Date of manufacture". If there is a printed date, it is more reliable than decoding the serial number.
Who makes Lennox?
Lennox is made by Lennox International.
How sure are these dates? Checked against official records (recall notices or data plates with printed dates). How we test the decoder.
Keeping an older furnace going
- Furnace air filter: Change it every 1 to 3 months. Check the size printed on the old filter.
- Carbon monoxide detector plug in: Any gas furnace, and especially an older one, should have a CO alarm nearby.
- Smart thermostat: Cuts run time on any system, old or new.