A.O. Smith Water Heater Age Lookup
A.O. Smith uses one consistent date code across ProLine, Vertex, Voltex, and its commercial lines. Enter any A.O. Smith serial number to get the precise build date and current age in seconds. Handy for spotting an aging tank before it fails.
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Finding Your A.O. Smith Serial Number
Works on ProLine, Signature, Signature Premier, and commercial models. Check these four spots.
Gas model shown. Spots are the same on A.O. Smith electric tanks.
Where to Look
ProLine and Signature gas models: the plate sits on the jacket above the gas control valve, near the bottom of the tank.
Commercial Cyclone and Vertex units: the plate moves to the side or the back panel instead of the front.
What You're Looking For
A.O. Smith prints a boxed grid signed A. O. SMITH CORPORATION with the plant city underneath (McBee SC here, or Ashland City TN and Johnson City TN). SERIAL NUMBER is the middle column of the top row, sitting beside the model number rather than above or below it, and that's the number to enter above. The ITEM ID / PART NUMBER in the third column is not the serial.
- A boxed grid with MODEL NUMBER, SERIAL NUMBER, and ITEM ID side by side across the top row
- The serial in the middle column, beside the model number and not underneath it
- Usually 10 to 13 characters, most often all digits (e.g. 1719106145074)
- A. O. SMITH CORPORATION and the plant city printed near the bottom
- The same serial repeated under the barcode at the bottom right, which helps when the printed row has faded
Can't find it? A.O. Smith also builds State, American, Reliance, and Whirlpool tanks on the same lines, so the plate sits in the same place on all of them. On electric models, look under the upper element cover.
A.O. Smith Serial Number Examples
Older factory formats put a plant code in front of the month letter, such as SK973804428S19 (October 1997) and the dashed MH92-0020943-S44 (August 1992), and both decode here too.
Don't worry if yours looks different. A.O. Smith has used week codes, month letters, and dashed factory codes across five decades, and our decoder handles all of them, including serials that start with a plant letter.
About A.O. Smith Water Heaters
A.O. Smith has been operating out of Milwaukee since 1874 and is the largest manufacturer and marketer of water heaters in North America. That reach is easy to miss from the outside. If you own a Lowe's Signature tank, a State or American unit, a U.S. Craftmaster, a Reliance, a Lochinvar, or an older Whirlpool, you own an A.O. Smith product built in the same plants under a different label.
The residential range splits by where it is sold. ProLine goes to plumbing wholesalers and ProLine XE adds the higher efficiency models; Signature and Signature Premier go to Lowe's. Both cover atmospheric and power vent gas, electric, gas tankless, and the Voltex heat pump series. Vertex is the condensing gas model, reaching up to 96 percent thermal efficiency for homes and light commercial work. Tanks use the Blue Diamond glass lining with a magnesium anode rod.
A.O. Smith serial numbers are not consistent, which is the main reason a page like this exists. The company has used at least ten distinct formats across its plants and eras. Most modern serials open with the two digit year and the production week, so 1719106145074 was built in week 19 of 2017. Others lead with one or two plant letters before the date, and older formats put the month in a trailing letter. One more quirk worth knowing: the capacity in an A.O. Smith model number is the DOE rated volume, which usually reads a gallon or two below the nominal size on the brochure.
Where to find the serial
Look at the rating plate on the upper third of the tank, usually a silver foil sticker near the cold inlet pipe. The serial sits below the model number and is labeled SERIAL or SER. NO. On commercial units the label is often on the side panel. A.O. Smith uses tall narrow stickers that tend to fade in attics, so a phone flashlight helps.
What the serial actually looks like
Why the age is worth knowing
A.O. Smith residential warranties typically run 6, 9, or 12 years on the tank depending on the line (ProLine, ProLine XE, Signature Premier). Commercial Cyclone and Vertex units have shorter coverage but longer expected service life. After year 10 on a residential tank, budget for replacement even if it still works.
Quick answers for this brand
Is A.O. Smith the same company as State and American Water Heater?
Yes, A.O. Smith Corporation owns State Industries and American Water Heater Company, and the three brands share manufacturing plants in Ashland City TN, McBee SC, and Johnson City TN. The serial number formats are nearly identical across all three brands.
What's the difference between an A.O. Smith ProLine and Signature?
ProLine is the contractor-only line sold through plumbing wholesalers, while Signature and Signature Premier are sold at Lowe's. The internal components are similar but warranty terms and a few features differ. Both decode the same way from the serial.
Where is the date code on a Vertex commercial A.O. Smith?
Commercial Vertex units use the same YYWW format in the first four digits of the serial, but the rating plate is on the side or back panel instead of the top. The serial may also include a leading letter for the plant code.
Time to repair or replace your water heater?
Compare free quotes from top-rated local pros near you.
Protect your water heater and 20+ home systems with a home warranty
Share this tool with friends!
Know someone with an aging water heater? Send them a free check.