Water Heater Age Decoder: Find Your Manufacture Date

Water heater age by serial number is easy to work out once you know your brand’s format: every serial number encodes the manufacture date, it’s just decoded differently by every manufacturer. Find the serial number on the rating plate (usually the upper third of the tank, or the front panel on tankless units), then match it to your brand below.

Illustration of accessing the fittings on top of a storage tank water heater, near where the rating plate is usually found.

Bradford White’s letter cycle repeats every 20 years, so a serial starting with the same letter could be from either decade — cross-reference with the model number’s other clues (or the unit’s general condition/wear) to pick the right decade.

Codes at a Glance

Code	Meaning
A.O. Smith / State / American / Lochinvar	First 2 letters = year and month, per A.O. Smith’s own registration lookup	Guide coming soon
Bradford White	First letter = year (a repeating 20-year letter cycle: L,M,N,P,S,T,W,X,Y,Z,A,B,C,D,E,F,G,H,J,K), second letter = month	Guide coming soon
Rheem / Ruud / Richmond	On older units (generally pre-2000), first 2 digits = month, next 2 = year. Newer serials use a different format — check Rheem’s own lookup tool.	Guide coming soon

FAQ

My hot water heater is 20+ years old. Should I replace it?

Most tank water heaters are designed for an 8–12 year service life; tankless units often last 15–20 years. Twenty-plus years on a tank is well past typical design life — replacement, even if it’s still technically working, is worth planning for.

Can you tell manufacture date from serial number?

Yes, on nearly every major brand — the format is just different for each one. See the table above for the three most common brands.

Is a 4-year-old water heater still good?

Yes — well within normal service life for either a tank or tankless unit, assuming no other symptoms.

Written by HotWater Decoded — water heater repair specialists. Technically reviewed by a licensed technician on our team.

Sources

InterNACHI’s water heater dating chart, A.O. Smith’s manufacturing-date lookup, and Bradford White’s own “My Water Heater” serial decoder