How old is my American water heater?

The main format

InspectApedia, with a photograph of the data tag: "serial number 9950123040. This serial number decodes to 1999 week 50."

Their second worked example: "9201 nnnnn would translate as 1992, first week, that is January 1 to 7 in 1992."

Fast Water Heater reaches the same rule independently, listing "American Water Heater, A.O. Smith, State, Reliance & Whirlpool" as one group where "the first two digits are the year, the next two are the week of that year."

InspectApedia adds one instruction that sounds obvious and is the most common mistake anyway: "Check the American-brand water heater serial number, not the model number."

The other two formats

The month letter on that third form uses the same A to M scale, with I left out, that InspectApedia documents for the A.O. Smith family: A is January through to M for December.

The case the rules do not cover

This is the part most decoders leave out, and InspectApedia states it rather than papering over it: "Note that this decoding won't work for older American Appliance Mfg. Corp. water heaters", citing a reader's label with serial number A 2363113.

Their method for those, which is reasoning rather than decoding:

• Start with the age of the building. InspectApedia: "That sets a reasonable floor under the question of heater age."
• Test each candidate reading against it. Their own worked reasoning on that serial: is A WWYY nnn, giving week 23 of 1963, plausible for this building? Or is A nnn WWYY, giving week 31 of 2013? They rule the second out: "from the brand name history as well as the label's appearance, we can be sure that this water heater is older than 2013."
• Use every other date on the unit. The newest year on any sticker sets a second floor.

Our note, marked as ours: this is the honest shape of the answer on a pre-1980s plate. A decoder that returns a confident date for serial A 2363113 is inventing one.

Who American is now

InspectApedia records the corporate chain: "The American Water Heater Company, founded around 1972, was merged into GSW in 2002 and in turn GSW later merged into AO Smith."

That chain is why this page and three others on this site share a decoding rule. It also explains a brand you may not expect to find here: American builds Whirlpool water heaters under licence, so a Whirlpool plate decodes by the rules above. The family's other pages are A.O. Smith and State, and State's page documents a genuine disagreement between the references that is worth reading before you trust any four-digit code in this family.

Turning a week into a month

From Fast Water Heater, who note the conversion is approximate because a week can straddle a month boundary:

What the age tells you

Week 50 of 1999 makes that photographed heater over twenty-five years old, which is well past any useful repair decision, and far beyond the point where the lifetime cost of keeping it running makes sense. For a unit in the normal range, the repair or replace page does the arithmetic and the age decoder handles the other brands.