Furnaces, AC and heat pumps

How old is my Lennox furnace, AC or heat pump?

Lennox serials start with a two-digit plant code that is often mistaken for the date. The year is the third and fourth digits and the letter after them is the month. Armstrong Air, AirEase, Ducane, Concord, Allied and Aire-Flo are Lennox companies and use the same rule on newer equipment.

How to read a Lennox serial number

Plant code, year, then month letter (1974 to today)

The first two digits are the factory, not the date. The next two digits are the year and the letter after them is the month (A is January, M is December, I is skipped).

5898G07568 reads as July 1998.

Two sources agree PickHVAC, Hunker, Waypoint Property Inspection, Energy Trust of Oregon furnace chart, InterNACHI inspector forum

Ten digits, date at the end (1990s to 2000s (some units))

On ten-digit all-number serials the seventh and eighth digits are the year and the last two are the week.

4140720328 reads as week 28 of 2003.

Two sources agree Building Intelligence Center, McGarry and Madsen Home Inspection, Energy Trust of Oregon furnace chart, PickHVAC

Where to find the serial number

Furnace: inside the front panel or on the side of the cabinet.
AC, heat pump or mini-split: the plate on the outdoor unit, usually near the line connections.
Use the line marked Serial No. or S/N, not the model number. If the plate prints a manufacture date, use that.

How long should it last?

Typical life of a furnace: 15 to 20 years

A gas furnace usually lasts 15 to 20 years. Well-maintained units in mild climates reach 25; units that run hard with dirty filters fail sooner.

How long does a furnace last? · Should I replace my furnace? · HVAC.com, Lennox, InterNACHI (15-25)

Typical life of a central air conditioner: 12 to 15 years

A central AC condenser usually lasts 12 to 15 years. In hot climates where it runs most of the year, 10 is more typical; in the north, 20 is possible.

How long does a central air conditioner last? · Should I replace my air conditioner? · Bryant, Lennox, InterNACHI (7-15)

Typical life of a heat pump: 10 to 15 years

An air-source heat pump usually lasts 10 to 15 years. It runs in both seasons, so it logs more hours than a furnace or an AC alone.

How long does a heat pump last? · Should I replace my furnace? · Trane, Lennox, Bryant, InterNACHI

Should I replace it?

Should I replace my furnace? · Should I replace my air conditioner?

More Lennox pages

Lennox furnace age · Lennox central air conditioner age · Lennox heat pump age

Parts that help it last

Furnace filters Check the size printed on the old filter and buy the same. A clogged filter is the most common cause of avoidable furnace trouble.
Leak alarm Useful near a high-efficiency furnace or an AC coil, where condensate drains can clog.

Check your model and size before you buy. Amazon links are affiliate links: as an Amazon Associate I earn from qualifying purchases.

Keep a record of your home

The age you just looked up is the kind of fact that gets lost. A written record of serial numbers, install dates, repairs and who did the work saves the next owner, inspector or insurer from guessing.

Keep This With the House

A lifetime logbook for the house, organized by system, with room for serial numbers, install dates, repairs and contractors. It stays with the house for the next owner.

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The House Has Old Pipes

Galvanized, polybutylene, cast iron and the sewer line: what fails, what it costs, what insurance won't cover and how to decide.

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The House Is Fifty Years Old

A buyer's guide to older homes: wiring, pipes, lead, asbestos, insurance refusals and what the repairs actually cost.