How old is my water heater? Finding the install date

A water heater has a date it was made and a date it went in. The install date is the one to log, because the heater's working life starts there. The date made is still useful: the heater can't have gone in before it was made, so it gives you the earliest possible start when the paperwork is missing. The City of Palo Alto asks residents to write down the manufacture date so they know when to plan ahead.

Source: City of Palo Alto, Check Your Water Heater's Age, checked October 20, 2026.

1. Invoice or receipt

   The installer's invoice has the date, and often the model and serial number too. Check the house binder and your email.

2. Home inspection report

   Bought the house? Inspection reports often note the heater's brand and age. It's a good cross-check even when you have the invoice.

3. Permit record

   If the heater went in under a permit, your city or county building department may have the date on file.

4. A sticker on the heater

   Some installers leave a sticker with their name and the date. Read it from the outside; don't move anything to look.

5. Ask whoever knows

   The previous owner, the landlord or the property manager may simply remember, or have the invoice.

The serial number is on the data plate, the label that also lists the maker and model. The label guide shows where to look. Each maker codes the date its own way. These are the formats the City of Palo Alto publishes, with its examples:

Source: City of Palo Alto, Check Your Water Heater's Age, checked October 20, 2026.

• Rheem: the first two digits are the month and the next two the year. 1209D01234 was made in December 2009.
• A. O. Smith, current serials: the first two digits are the year and the next two the week. 203707002601001 was made in early September 2020.
• A. O. Smith, before 2008: the second character is a month letter (A is January, B is February and so on, skipping I), then two digits for the year. 2C062938405 was made in March 2006.
• Bradford White: the first letter is the year and the second the month. The year letters repeat every 20 years, so HK16433183 is October 2011, or October 1991 on a much older heater. The label's condition and your paperwork tell you which.

Source: City of Palo Alto, Check Your Water Heater's Age, checked October 20, 2026.

Any other brand: look on the maker's website or call their customer line with the serial number. Write down where the answer came from next to the date.

Source: City of Palo Alto, Check Your Water Heater's Age, checked October 20, 2026.

On the heater record, write the date installed and where it came from (invoice, report, permit). If all you have is the serial number, write the date made and mark it "made, not installed". The estimator's 13-year mark is the average life on the PNNL page: a planning date for the binder, not a verdict on your heater.

Source: PNNL Building America, DHW First Hour Rating, checked October 19, 2026.

• Tip 01

  Photograph the plate before you decode

  Copying a long serial in a dim closet is where mistakes happen. Zoom in on the photo instead.

• Tip 02

  Check the letter cycle on Bradford White

  The same year letter covers two years two decades apart. An invoice or the inspection report settles it.

  Source: City of Palo Alto, Check Your Water Heater's Age, checked October 20, 2026.

• Tip 03

  Note the source of every date

  A date from an invoice is firmer than one decoded from a serial number, and a plumber or buyer will ask which you have.

• Tip 04

  Ask for the invoice when it's replaced

  When a new heater goes in, keep the invoice with the record. The next owner or tenant won't have to decode anything.

This page is one part of a bigger job. The system page puts the parts in order.

• SystemWater heater size and age recordOne page for your water heater: copy the label and data plate, find the install date, check the first hour rating against your busiest hour, log every visit.9 steps · 5 parts · 1 page to printOpen the system

• Chapter 01Water heater capacity estimatorAdd up your busiest hour of hot water, check it against the first hour rating on the EnergyGuide label, and print a record of your heater.Open the tool
• ProblemNo size printed on my air filter: how to find itThe print on the frame is gone or the slot is empty. Measure the opening, round to the nearest inch, and know when you need a custom size.Read the guide
• Practical noteWhat to change on move-in day: locks, garage opener and codesNew house, old keys. Here's the order to work in on move-in week: count what you got, change the locks, clear the garage opener, reset codes, then cut copies.Read the guide
• Chapter 01All records toolsPrintable home records with a calculator behind each one: appliance and warranty log, HVAC filter sizes and change dates.Open the chapter

• Check Your Water Heater's Age, City of Palo Alto Utilities. Checked October 20, 2026.
• DHW First Hour Rating (RED Calc tool), Pacific Northwest National Laboratory, Building America Solution Center (U.S. Department of Energy). Checked October 19, 2026.

Every outside number on this page names its source and the date we checked it. See them all on the sources page. Spotted an error? Tell us.