How Old Is Your GSW Water Heater?
GSW is A.O. Smith's Canadian brand, so GSW and John Wood water heaters use the same serial number date code as their US siblings: the manufacture date is encoded in the first digits of the serial. Enter your serial number in the free decoder above for an instant answer, or follow the guide below to read it yourself.
Where to Find the Serial Number
Check the rating plate on the side of the tank — a silver or white sticker, usually in the upper half, that lists the model number and serial number together. The date lives in the serial, not the model number. On older tanks the sticker can fade; a phone photo with the contrast bumped usually makes the first four digits readable.
How the GSW Serial Format Works
The date code is year, then week, in the first four digits:
Worked example — 1916A003841:
19= 2019 (year)16= week 16 (mid-April)Aand the remaining digits = factory and production sequence- Result: manufactured in week 16 of 2019
Letter prefixes. Some serials start with letters, or insert a letter inside the date block — these are factory or product-line codes, not part of the date. Skip leading letters and read the first four digits you find.
The two-digit year can mean two decades — 19 is 2019 on most units but could be 2009 on an older line. Compare the unit's condition and model. When in doubt, our decoder lists every plausible year instead of guessing.
Why Your GSW Water Heater's Age Matters
- Lifespan. Tank water heaters average 8–12 years of service. Past that, internal corrosion makes tank failure — and a flooded basement — far more likely.
- Warranty. GSW tanks carry standard 6- and 12-year warranty tiers counted from the manufacture date, not the install date. The serial tells you whether a repair might still be covered.
- Replacement planning. A unit past 10 years is on borrowed time. Knowing the date lets you shop for a replacement calmly instead of during an emergency.
Sources
Brand ownership verified against A.O. Smith's corporate history and the InterNACHI water heater dating chart; serial format follows A.O. Smith's manufacturing-date guidance.