Water heaters

How old is my A.O. Smith water heater?

A.O. Smith is the largest water heater maker in the United States and the parent of State, American, Whirlpool, U.S. Craftmaster, Reliance, Kenmore, Lochinvar and Takagi. Since about 2008 every A.O. Smith-made tank uses the same year-and-week serial, so the rule below also works on most of those brands. Older A.O. Smith serials used a month letter instead.

How to read a A.O. Smith serial number

Year and week (current)

The first two digits are the year and the next two are the week of that year. An S in front is a factory code and is ignored.

1210A002243 reads as week 10 of 2012.

Two sources agree Building Intelligence Center, City of Palo Alto Utilities

Two characters, then the year (older, ended about 2008)

The second character is a month letter. The two digits after it are the year.

AF04A093001 reads as June 2004.

Two sources agree Building Intelligence Center, InterNACHI water heater dating chart, City of Palo Alto Utilities

Month letter, then the year (older, ended 2008 to 2010)

The first letter is the month (A is January, M is December, I is skipped). The two digits after it are the year.

E07A135491 reads as May 2007.

Two sources agree Building Intelligence Center, Working RE

Where to find the serial number

Water heater: the rating label on the side of the tank, near the EnergyGuide sticker. On a tankless unit it is on the side or bottom of the cabinet.
Use the line marked Serial No. or S/N, not the model number. If the plate prints a manufacture date, use that.

How long should it last?

Typical life of a tank water heater: 8 to 12 years

A standard tank water heater usually lasts 8 to 12 years. Some make it to 15 with soft water and a replaced anode rod; some fail at 7.

How long does a tank water heater last? · Should I replace my water heater? · DC Dept. of Energy & Environment, InterNACHI

Should I replace it?

Should I replace my water heater?

Other brands in this group

American Water Heater · U.S. Craftmaster · Bradford White · State · Reliance · Kenmore · Whirlpool · Rheem · Ruud · Richmond · GE · Marathon · Rinnai · Navien · Noritz · Takagi · Bosch (tankless water heater) · Lochinvar · GSW / John Wood · Paloma · HTP / Westinghouse / American Standard (water heaters) · Giant · EcoSmart / Eemax · Stiebel Eltron

Parts that help it last

Anode rod The sacrificial rod that rusts instead of the tank. Checking it every few years is the cheapest way to add life.
Flush kit A hose and fittings for draining sediment from the bottom of the tank once a year.
Expansion tank Soaks up pressure swings in a closed plumbing system. Ask a plumber whether yours needs one.
Leak alarm A small alarm that goes on the floor beside the heater and warns you before a slow leak becomes a flood.

Check your model and size before you buy. Amazon links are affiliate links: as an Amazon Associate I earn from qualifying purchases.

Keep a record of your home

The age you just looked up is the kind of fact that gets lost. A written record of serial numbers, install dates, repairs and who did the work saves the next owner, inspector or insurer from guessing.

Keep This With the House

A lifetime logbook for the house, organized by system, with room for serial numbers, install dates, repairs and contractors. It stays with the house for the next owner.

Paperback

The House Has Old Pipes

Galvanized, polybutylene, cast iron and the sewer line: what fails, what it costs, what insurance won't cover and how to decide.

Paperback · Kindle

The House Is Fifty Years Old

A buyer's guide to older homes: wiring, pipes, lead, asbestos, insurance refusals and what the repairs actually cost.

Paperback · Kindle

Book links are Amazon affiliate links.