About
How Old Is That reads the build date hidden in a serial number. Manufacturers encode the date so their warranty and service teams can look it up. The rules are public but scattered across service bulletins, recall notices and forum threads. This site puts them in one place and shows its work.
Who runs it
How Old Is That is built and run by Graham Calihan. It is an independent site, not connected to any manufacturer, retailer or installer. Corrections and brand requests go straight to me through the form below.
Where the rules come from
Each format links to its sources. We start from manufacturer documents and U.S. Consumer Product Safety Commission recall notices, which pair real serial numbers with real build dates. Where a maker has not published its format, we use references that home inspectors rely on and check them against each other. When sources disagree, we say so on the brand page.
Every rule is tested against serial numbers taken from those sources before it goes live.
Recall checks use a hand-curated list built from CPSC recall notices for water heaters and HVAC equipment. Many recalls depend on the model number, so a match means "check this notice", not a final answer. For the full list, search cpsc.gov.
What it can't tell you
- The install date. A unit can sit in a warehouse for months before it goes in.
- The condition. A well-kept 14-year-old tank can outlast a neglected 8-year-old one.
- Warranty coverage. That depends on the registration and the original paperwork.
How the site makes money
The checkers are free. Some result pages link to parts stores and other services through partner programs, and if you buy through one of those links we may earn a commission at no extra cost to you. Partner links are marked where they appear. They never change what a checker reports. Full details are in the terms.
Your data
Serial numbers are decoded in your browser. Photos are read on your device and never uploaded. If you answer "Was this right?", we keep the serial and your answer to improve the rules. Details are in the privacy notice.
Contact
Found a wrong date, or want a brand added? Send a note.