How old is my water heater, furnace or AC?

Where to find the serial number

Every water heater, furnace, air conditioner and heat pump sold in the US has a rating label (also called a data plate) listing the model number and the serial number. You want the line marked Serial, S/N or Serial No.. The model number (M/N) describes what the unit is; the serial number identifies the individual unit and, for most brands, encodes when it was built.

• Tank water heaters: on the side of the tank, usually above the gas control valve on gas models or near the upper heating-element cover on electric models.
• Furnaces: inside the lower blower door or on the side of the cabinet. Switch the power off at the service switch before you take a panel off.
• Air conditioners and heat pumps: on the outdoor unit, typically on the side panel that covers the electrical connections. The indoor coil or air handler has its own label and its own date.

Take a photo of the label with your phone and zoom in. It's much easier than reading faded print with a flashlight, and it gives you a record for warranty claims later.

How the serial number shows the age

Manufacturers build the production date into the serial so they can trace warranty claims and recalls. There is no industry standard, so each brand family does it differently:

• Year and week: Carrier, Bryant and Payne serials start with the week and then the year, so 2406… means week 24 of 2006. A. O. Smith and State reverse it: year first, then week.
• Year and month: Goodman, Amana and Janitrol serials start with the year and month, so 0601… means January 2006. Rheem water heaters put the month first.
• Letter codes: Bradford White uses one letter for the year and one for the month. Lennox puts a month letter after a two-digit year.

Brands owned by the same company usually share a format, which is why the tool decodes Bryant and Payne the same way as Carrier. Formats also change over the decades, so one brand may have two or three eras of serials. Our methodology page lists every format we read and how far back each one goes.

How long do water heaters, furnaces and AC units last?

The tool compares your unit's age with the typical service life for that kind of equipment. These are averages for normally maintained equipment in typical US homes:

Hard water, a tank that has never been flushed, an oversized or undersized system, coastal salt air and skipped maintenance all push equipment toward the short end of the range. Annual service and, for tank water heaters, replacing the anode rod can push it toward the long end.

What to do with your result

• Under about three-quarters of its typical life: keep up routine maintenance. A big repair is usually worth doing.
• Approaching its typical life: start setting money aside and get quotes before anything goes wrong, so a failure doesn't force a rushed, expensive decision.
• Past its typical life: think hard before paying for major repairs. A common rule of thumb is to replace when the repair costs more than half the price of a new unit, or when age in years multiplied by the repair cost is more than the cost of replacement.

Buying or selling a house? The age of the water heater and HVAC system is one of the first things a home inspector notes. Checking it yourself before the inspection means no surprises in the negotiation.

Brands we decode

Water heaters: A. O. Smith, American Water Heater, Bradford White, GE, Kenmore, Navien, Noritz, Reliance, Rheem, Richmond, Rinnai, Ruud, State, Whirlpool.

Furnaces, air conditioners and heat pumps: AirEase, Amana, American Standard, Arcoaire, Armstrong Air, Bryant, Carrier, Coleman, Comfortmaker, Concord, Daikin, Day & Night, Ducane, Frigidaire (HVAC), Goodman, Heil, Intertherm, Janitrol, Lennox, Luxaire, Maytag (HVAC), Miller, Nordyne, Payne, Rheem, Ruud, Tempstar, Trane, York.

Need the size instead of the age? Our model number tools read tonnage and furnace BTU. More brands are being added every month. If yours isn't listed, send us the brand and serial and we'll prioritize it.

Frequently asked questions

Can I find out how old my water heater is without the serial number?

Sometimes. Many rating labels print a manufacture date directly, and installers often write the install date on the tank or the label. If neither is there and the label is unreadable, the age of the house, permit records or the warranty registration are your next best clues.

Is the manufacture date the same as the install date?

No. Units usually sit in a warehouse or supply house for a few weeks to a few months before they are installed, and occasionally longer. For lifespan planning the difference rarely matters; for warranty claims, the install date (or your receipt) is what manufacturers go by.

Why does the tool say my serial could mean two different dates?

Some brands use a letter or single digit for the year, and those codes repeat (Bradford White every 20 years, for example). Where the serial has another clue, such as the length of the Bradford White sequence number, we use it. When nothing settles it, we show the most recent possible date first and list the older possibility, so check which fits your unit.

My furnace is older than its typical lifespan. Do I have to replace it?

Not automatically. A well-maintained unit can run years past the average. Age is a planning signal: it tells you to budget for a replacement and weigh repair costs carefully, so you are choosing on your schedule instead of during a breakdown.

Do you store the serial numbers I enter?

No. The lookup runs entirely in your browser; the serial is never sent to our server. The only time we receive a serial is if you choose to send one through the Report a Wrong Result form.

Decoder rules last reviewed 2026-10-18. Results are estimates. See our disclaimer.