How to Tell the Age of a Water Heater

The quickest way to tell a water heater's age is the rating label on the side of the tank. It either prints the manufacture date or hides it in the serial number. Here's how to find and read it for any brand.

Updated 2026-10-19

Step 1: Find the rating label

Every water heater sold in the US has a rating label (also called a data plate) on the outside of the tank. It lists the brand, the model number, the serial number, capacity, fuel, input rating and certification marks.

• Gas tanks: the label is usually on the front, a hand’s width above the gas control valve and burner access door.
• Electric tanks: look between the upper and lower heating-element covers, or near the top.
• Tankless: on the side of the cabinet, or inside the front cover.
• Heat pump water heaters: on the tank jacket, sometimes near the top below the compressor section.

If the heater is in a tight closet or against a wall, use your phone camera. If the label has faded, a photo with the flash off and the contrast turned up often makes it readable.

Step 2: Look for a printed date

Before decoding anything, read the whole label. Many newer labels print the manufacture date directly, as MFG DATE, MFD, DATE OF MFR or a month and year (MM/YYYY). If yours has one, that’s your answer.

Also look for handwriting. Installers often write the installation date on the tank, the label or the cold-water pipe in marker, and some leave an installation sticker with their company name.

Step 3: Decode the serial number

If there’s no printed date, the serial number almost always contains it. Each brand family uses its own code:

Common mistakes

• Reading the model number instead of the serial. The model number describes the product (fuel, gallons, warranty) and doesn’t change between units. The serial is unique to your heater.
• Mixing up O and 0, or I and 1. Most brands avoid the letters I and O in date codes for exactly this reason.
• Forgetting the letters at the start. On Bradford White serials the letters are the date; on Rheem serials you have to skip past them.
• Assuming week means month. A. O. Smith’s 1335 is week 35, which is late August, not “month 35”.

Step 4: If there’s no label at all

• Paperwork: receipts, the warranty registration card, or the home inspection report from when you bought the house.
• Permit records: many cities and counties require a permit to replace a water heater. Your local building department can often look up permits by address.
• The manufacturer: if you have a model number but no readable serial, customer support may still be able to estimate the production period from the model.
• Visual clues: older gas tanks without a sealed combustion chamber, or tanks with no flame-arrestor design, generally predate the mid-2000s.

What to do with the age

Once you know when it was made, compare it with the typical lifespan: about 8 to 12 years for a tank and 15 to 20 years or more for tankless. Our guides on how long water heaters last and when to replace one walk you through the next step.