Buyer guide
The age of the heating and air, water heater and roof tells you what you may be replacing in the next few years, and what to budget for. Here's how to find out how old each system is, and how long each one typically lasts.
Tip: turn your phone sideways or open this page on a tablet or computer to see the tables and tools at full size.
Step 1
The easiest answers are often already written down. Check these before you start reading serial numbers.
Step 2
Almost every system has a data plate or sticker with the brand, model number and serial number. Many print the manufacture date right on it. Snap a photo of each label so you can look things up later.
| System | Where to find the label |
|---|---|
| A/C or heat pump (outside unit) | On a side panel, usually near where the electrical lines go in |
| Furnace or air handler (inside unit) | Inside the front access door, or on the side of the cabinet; often in a closet, attic, basement or crawlspace |
| Water heater | On the side of the tank, or on the front of a tankless unit |
| Electrical panel | Inside the panel door; individual breakers are often date-stamped |
| Appliances | Inside the door frame of the refrigerator, dishwasher, oven and washer, or on the back |
Don't open electrical panels or remove covers yourself. Read what you can see, and let your home inspector handle the rest.
Step 3
If there's no date on the label, the serial number usually holds it. Here are the most common formats. Brands change formats over the years, so when in doubt, call the manufacturer with the serial number or ask your inspector or HVAC tech.
| Brand | How to read the serial number | Example |
|---|---|---|
| Carrier, Bryant, Payne | 1st and 2nd digits are the week; 3rd and 4th are the year | 2219E12345 = 22nd week of 2019 |
| Trane, American Standard (2010 on) | 1st and 2nd digits are the year; 3rd and 4th are the week | 19451ABCDE = 45th week of 2019 |
| Goodman, Amana, Daikin | 1st and 2nd digits are the year; 3rd and 4th are the month | 1905123456 = May 2019 |
| Lennox | 3rd and 4th digits are the year (the first two are the factory) | 5819C12345 = 2019 |
| Rheem, Ruud | After the first letter: 2 digits for the week, then 2 for the year | W121912345 = 12th week of 2019 |
| York, Coleman, Heil and others | Formats vary; use the brand's website or ask your HVAC tech | |
The label on the outside unit lists the refrigerant. R-22 means the system was made before 2010, when new R-22 equipment was banned. R-22 is no longer produced, so recharging an old system is expensive. R-410A systems were standard from about 2010 to 2024, and most new systems installed from 2025 on use R-454B or R-32.
A central system has an outside unit and an inside unit, and they aren't always the same age. Sometimes only one was replaced. Read both labels.
Step 4
Water heater labels often show the date outright. If not, the serial number works the same way.
| Brand | How to read the serial number | Example |
|---|---|---|
| Rheem, Ruud, Richmond | The first four numbers are the month and year | 0519123456 = May 2019 |
| A.O. Smith, State, American, Reliance (2008 on) | The first four numbers are the year, then the week | 1915A123456 = 15th week of 2019 |
| Bradford White | The first two letters stand for the year and month on a repeating 20-year cycle; look up the chart on Bradford White's site or ask your inspector | |
Also look for rust at the base, water on the floor, and a missing drain pan or discharge pipe on the relief valve. Your inspector will check these too.
Everything else
There's no label, so rely on the seller's disclosure, receipts and permits. Your inspector or a roofer can estimate age from wear: curling, cracking and bare spots where granules are gone. More on roofs →
Look inside the panel door for a date, and note the brand. Federal Pacific (Stab-Lok) and Zinsco panels have a history of problems, and some insurers won't cover them.
The manufacture date is printed on the back. Replace smoke alarms every 10 years, and carbon monoxide alarms every 5 to 7 years or when the label says.
Search the brand name plus "serial number age," or enter the serial on the manufacturer's support site. Many will tell you the build date.
Planning ahead
Once you know how old something is, compare it with how long it typically lasts: 10 to 15 years for an air conditioner or heat pump, 8 to 15 for a water heater, 15 to 30 for asphalt shingles.
Typical lifespans for every system, roof and appliance →Get it checked
Your home inspector will usually note the age and condition of the major systems in the report. For a closer look at an older system, an HVAC company, plumber or roofer can tell you how much life is left.