How old is it? Read the age from the serial number

Every furnace, air conditioner, water heater and major appliance carries its build date inside the serial number, in a code that differs from brand to brand. Choose the brand, type the serial, and get the month and year it was made.

How it works

1. Find the rating plate. It is the label that lists the model number and the serial number. The equipment pages show where to look, and the rating plate guide explains its lines.
2. Choose the brand printed on the unit and type the serial number. Spaces and dashes do not matter.
3. Read the date. The decoder shows which characters hold the year, month or week, so you can check the result against the plate.

The decoder knows 39 serial formats from 41 brands, including formats that were retired years ago. Each one is tied to the manufacturer document or the independent references it was checked against. See method and sources.

What the age tells you

Age matters because equipment wears out on a fairly predictable schedule. These are typical service lives. The linked pages give the sources and the signs that a unit is near the end.

Sizing the replacement

When the date says a unit is near the end of its life, the next question is what size to replace it with. The model number on the rating plate gives the size of the unit you have now: use the model number decoder to read it.