Where to Find the Serial Number on a Water Heater

The serial number is on the water heater's rating plate. Here is what that label looks like, what to copy from it, how to photograph it, and what to do if it is unreadable.

Last updated: 9 November 2026

The serial number is on the water heater's rating plate, a label attached to the outside of the unit. Bradford White says your model number and serial number are located on the rating plate, and A.O. Smith says the serial number can be found on the rating plate. The plate is also called the data plate or rating label. Different names, same label.

What the rating plate looks like

It is a printed label covered in small text. Most of that text is regulatory and technical detail you can ignore. Three lines matter for finding the age:

• Model number. Identifies the product line. It is not the date code, but you need it if you contact the manufacturer or look up parts.
• Serial number. A string of letters and digits unique to your unit. For many brands, the build date is encoded in it.
• Capacity. The tank size, usually in gallons. It helps confirm you have the right label if there is more than one tank.

Labels are laid out differently by brand, so the lines may not be in the order shown in the diagram. Look for the words "model" and "serial" rather than relying on position.

Where to look on your unit

Plate positions differ by manufacturer and model, so use a short search rather than one fixed spot:

1. Start with the outer casing. Scan the front and sides at several heights, not just at eye level.
2. Look past anything in the way. Pipes, a wall, shelving, insulation blankets and stored boxes can hide a label.
3. Use a flashlight. Water heaters are often in dim corners, and a label can be hard to see without light from the side.
4. Ignore the yellow EnergyGuide sticker if there is one. It is a different label from the rating plate.

Do not remove panels or touch wiring or gas connections to find the plate. If you cannot see it, check the manual or call the manufacturer or a plumber.

What to copy down

Write down or photograph these exactly as printed:

• The brand name at the top of the plate.
• The model number.
• The full serial number, letters included. Do not drop leading letters or skip a character you think is unimportant.
• The capacity line, in case you need to tell two units apart.

Copy the brand because each manufacturer formats serial numbers differently, so the same string decodes differently under another brand's rules. The serial number age guide covers the formats.

How to photograph it so you can read it

A photo is better than a transcription, because you can zoom in later and a mistyped character can be checked against it.

• Take one photo of the whole plate, then a second close-up of just the model and serial lines.
• Hold the camera square to the label. Shooting from an angle blurs one edge.
• Avoid the flash pointing straight at a shiny label, since it washes out the print. Light from the side, or move a phone torch around until the glare moves off the text.
• Tap the screen to focus on the print, and check the result by zooming in before you walk away.
• Photograph the unit in place as well, so you remember which heater it was in a house with more than one.

Letters that look alike are the usual trouble: zero and capital O, one and capital I, five and S. Where it is ambiguous, note both readings and try each in the decoder.

If the plate is unreadable or missing

• Faded or scratched print. Try raking light from the side, or a photo with the contrast raised. Wipe off dust with a dry cloth. Avoid scraping or solvents that could remove what is left.
• Brand still legible, serial not. The model number rarely gives a build date, so this route may only give a rough range. Try the manual or warranty registration, a second label if the model has one, or a home inspection report, then contact the manufacturer.
• Plate gone entirely. Look for paperwork: the installation invoice, a warranty card or a permit record. These can give an installation date. That is not the build date. The heater was made before it was installed, so it is at least that old. Check that the paperwork refers to this unit and not one it replaced.

Whatever you end up with, treat the age as approximate and say so if you pass it on, for example when you check the water heater when buying a house.

Once you have the serial number

For how date codes are built and why brands differ, read Water Heater Age by Serial Number. If your plate says Bradford White or A.O. Smith, the Bradford White decoder and the A.O. Smith decoder take the serial and give a build date. Other brands start from the appliance age finder. Furnaces and air conditioners use a different label, covered in the HVAC data plate guide.