THE SHORT VERSION
- Find the rating plate: a printed label on the front of a tank (on gas models, near the gas valve) or on the side of a tankless unit. Photograph it.
- Know the brand before you decode. Rheem, Ruud, Richmond and GE tanks start with month then year (1209… = December 2009). A.O. Smith, State, American, Reliance and Whirlpool start with year then week (1210… = week 10 of 2012).
- Bradford White uses two letters: year, then month. JC… is March 1992 or 2012; the letters repeat every 20 years, and the length of the number after them settles it.
- Can’t decode it? Call the manufacturer with the model and serial, or use its online warranty check. Bradford White’s returns the manufacture date.
- Why it matters: tanks are expected to last roughly 8–15 years, and if you can’t prove the install date, warranties count from the manufacture date.
Three steps to your heater’s age
Find the rating plate
Look for a printed label with “Model” and “Serial” on it. On a tank it is on the front: about mid-height on electric models, often near the gas valve on gas models. On a tankless unit it is on a side panel.
Check for a printed date
ENERGY STAR notes that some labels print the manufacture date next to the serial number. If yours does, you’re done.
Decode the serial number by brand
Use the table below. If the brand is a store label (Kenmore, Richmond, GE), look for the actual maker’s name on the plate.
The code gives the date the heater was built, not installed; a unit can sit in a warehouse first. An invoice, permit record or home inspection report with the install date is better for warranty purposes.
What the rating plate tells you
The rating plate (also called the data plate) is the heater’s ID card. Bradford White’s example plate for a 40-gallon gas tank shows what a typical one carries.
- Manufacturer
- Who built it. On store brands, the clue to which code to use.
- Model number
- What it is: series, capacity, fuel, burner or element size.
- Serial number
- Which unit it is and, in almost every brand, when it was built.
- Capacity and input
- Nominal gallons; burner BTU per hour and gas type, or voltage and element wattage on electric models.
- Pressures and clearances
- Gas and water pressure ratings and minimum clearance to combustibles.
- Standard
- The safety standard and its edition, such as ANSI Z21.10.1-2013. A heater can’t be older than the standard it was certified to.
How each brand codes the date
Almost every US brand puts the date in the first few characters of the serial number, but the order differs. Each example below comes from a manufacturer document, a government recall notice or an inspector reference, as marked.
| Brand family | Where the date is | Example | Reads as | Source |
|---|---|---|---|---|
| Rheem, Ruud, Richmond, GE (tanks) | 1st–2nd digits month, 3rd–4th year (skip any leading letters) | 1209D01234 | December 2009 | Rheem (manufacturer) |
| A.O. Smith, State, American, Reliance, U.S. Craftmaster, Whirlpool (about 2008 on) | 1st–2nd digits year, 3rd–4th week | 1210A002243 | Week 10 of 2012 (early March) | CPSC recall notice; inspector references |
| A.O. Smith before about 2008 | 2nd letter month, then 2-digit year | AF04A093001 | June 2004 | Inspector references |
| State before about 2008 | 1st letter month, then 2-digit year | C05… | March 2005 | Energy Trust of Oregon decoder |
| Bradford White | 1st letter year (20-year cycle), 2nd letter month | JC16433183 | March 2012 | Bradford White (manufacturer) |
| Rinnai (2009 on) | 1st letter year, 2nd letter month | LM.BA-152112 | December 2019 | Inspector reference; serial format from Rinnai |
| Navien | Year, month, day after the 5-character model code | 7410x 18709 xxxx | July 9, 2018 | Health Canada recall notice |
| Noritz | 4-digit year, then month | 2005.06-004472 | June 2005 | Inspector reference (low confidence) |
Month letters run A = January to M = December, skipping I (J = September), per Bradford White’s chart; some third-party charts count I. Sources: Rheem; CPSC recall 19-029 via Consumer Reports; Bradford White; Health Canada; Rinnai TB-179; Building Intelligence Center and Energy Trust of Oregon decoders.
Rheem, Ruud, Richmond and GE
Rheem says its serial numbers have 10 characters: two digits for the month, two for the year, a plant letter, then a sequence. 12 09 D 01234 is December 2009. Rheem’s 2008 tankless warranty for Rheem and Ruud units agrees: “The first four digits of the unit’s serial number represent the month and year it was manufactured.”
- Ruud is Rheem’s sister brand, and Richmond is Rheem’s retail brand; its website is run by Rheem Manufacturing Company.
- GE tanks sold at Home Depot have been built by Rheem since 1999, per the trade press at the time. Inspector references read them with Rheem’s code: GE 0902 2246884, skipping the letters, is September 2002. Confidence: medium; check the maker named on your plate.
- Skip leading letters such as RU, RH or RHNG. RU 0904 B21710 is September 2004.
- First two digits 13 or higher? They can’t be a month. Inspector references list a few Rheem and Ruud styles, including some heat pump units, that put the week first. Call Rheem with the serial.
A.O. Smith, State, American and related brands
A 2018 federal recall of A.O. Smith gas water heaters covered units sold as American, A.O. Smith, Kenmore, Reliance, State, U.S. Craftmaster and Whirlpool, defined by serial number “where the first four digits represent the year and week of production,” from 1115 to 1631 (week 15 of 2011 to week 31 of 2016). To turn a week into a month, divide by 4.3: week 10 is early March.
- Before about 2008, A.O. Smith serials usually started with two letters; the second is the month and the two digits after it the year. State used one month letter and a year (C05…, March 2005). American already used year then week (9746…, week 46 of 1997, per Energy Trust of Oregon).
- Lochinvar is an A.O. Smith brand that sells residential water heaters. Inspector references list nine Lochinvar serial styles, from year-week (1142N012345, week 42 of 2011) to a letter code on old units. Confidence: low; call Lochinvar.
Bradford White
Bradford White publishes its own chart: the first letter is the year, the second the month, and the rest is a production number. JC16433183 is J = 2012, C = March. The year letters skip I, O, Q, R, U and V, leaving 20, so the cycle repeats every 20 years. The next section shows how to tell the cycles apart.
Kenmore and other store brands
Kenmore water heaters were made by several companies, including A.O. Smith, State and Rheem, according to the Building Intelligence Center. Read the manufacturer named on the plate and use that company’s code. An older A.O. Smith-built Kenmore, J06A059461, reads as September 2006; one built in 2011–2016 used year-week, as the recall shows. If no maker is named, a plumber can usually tell from the heater’s design.
Tankless: Rinnai, Navien, Noritz
- Rinnai serials look like LM.BA-152112, the format in Rinnai’s own technical bulletin. Per the Building Intelligence Center, since 2009 the first letter is the year (A = 2009, L = 2019, W = 2026) and the second the month: LM is December 2019. Rinnai uses R (2023), which Bradford White skips, so don’t mix the charts. Older Rinnai serials use digits (04.03, March 2004).
- Navien puts year, month and day after a five-character model code. Health Canada’s 2018 recall notice: “The first two digits identify the year, the next single digit identifies the month, and the last two digits identify the day.” October is X; inspector references give Y and Z for November and December.
- Noritz serials such as 2005.06-004472 appear to start with year and month (June 2005). That comes from one inspector reference; confirm with Noritz.
Bradford White’s letters repeat every 20 years
A Bradford White heater built this year starts with C, the same letter as one built in 2006; Bradford White’s chart lists C as “2006 or 2026.” Three checks settle it.
Count the digits after the two letters
Bradford White says the production number was “seven digits in length before December 2007 (DM), and eight digits in length after.” Eight digits means December 2007 or later.
Read the standard edition on the plate
A heater certified to ANSI Z21.10.1-2013 can’t date from 1993. This is our reasoning, not a Bradford White rule.
Use the warranty check
Enter the serial in Bradford White’s online warranty check, which reports the manufacture date.
One oddity: Bradford White says a computer error produced some serials starting OA, though O is not a year letter. Those heaters were built in January 1997.
When you can’t read or decode the number
Labels fade, peel and sit behind pipes. Before you guess, work through these in order.
Ways to find the date without decoding
- Manufacturer’s online warranty check. Bradford White’s returns the manufacture date. Rheem and A.O. Smith also look up warranties by serial number.
- Call the manufacturer with the brand, model and serial; send a photo if a character is hard to read.
- Paperwork: the installer’s invoice, a warranty registration email, or your home inspection report.
- Your local permit office, if a permit was pulled when the heater was installed.
- A plumber, who can usually read a damaged plate and identify the maker by design.
What the age tells you
Age is the tiebreaker in most repair decisions, and it sets your warranty status. Expected-life figures differ by source:
| Type | Rheem | ENERGY STAR | DOE Energy Saver |
|---|---|---|---|
| Gas or electric tank | 8–12 years | 10–12 years | 10–15 years |
| Heat pump (hybrid) tank | not stated | 13–15 years | not stated |
| Tankless | 15–20+ years | not stated | more than 20 years |
Sources: Rheem lifespan article (March 2026); ENERGY STAR (2024); DOE Energy Saver (archived June 2026). Water quality and maintenance move these a lot; see how long water heaters last.
- Past about 10 years (tank): ENERGY STAR says that if your heater is more than 10 years old, “it is time to consider replacing it before you’re left with an emergency decision.” Rheem says units over 10 are more likely to fail again soon after a repair. See repair or replace.
- Warranty status: coverage runs from the install date if you can prove it. If you can’t, Rheem and A.O. Smith start the clock 90 days after manufacture, and Navien six months after. The decoded date can decide whether a leaking tank is replaced free; see the warranty guide.
- Recalls are defined by serial ranges, like the A.O. Smith recall above.
- Near the end of the range? Get quotes while you still have hot water. See water heater replacement cost.
Common questions
Where is the serial number on a water heater?
On the rating plate: a printed label on the front of a tank or the side of a tankless unit. On A.O. Smith-group gas tanks it sits next to the gas control valve; Rinnai and Navien put it on a side panel.
How do I read a Rheem water heater serial number?
The first two digits are the month and the next two are the year, after any leading letters. Rheem’s example 1209D01234 was built in December 2009. Ruud, Richmond and GE tanks made by Rheem use the same code.
How do I tell the age of an A.O. Smith or State water heater?
On heaters made since about 2008, the first two digits are the year and the next two the week. A serial starting 1210 was made in the 10th week of 2012. Older units use a letter for the month followed by a two-digit year.
Is a Bradford White serial starting with C from 2006 or 2026?
Count the digits after the two letters. Bradford White used seven digits before December 2007 and eight after, so C plus eight digits means 2026. Its online warranty check also returns the manufacture date.
Is the manufacture date the same as the install date?
No. The serial shows when the heater was built; installation may be months later. Without proof of the install date, Rheem and A.O. Smith start the warranty 90 days after manufacture.
Sources
Sources checked October 4, 2026. Prices, codes and rebates change. Check current details with your installer and local permit office.
- How to locate and read your Rheem water heating serial numbers (2025) ↗ · Rheem
- Tankless gas water heater warranty AP13268-3 (2008) ↗ · Rheem, hosted by Home Depot
- Heat pump water heater warranty AP18539 (2016) ↗ · Rheem, hosted by Home Depot
- Warranty registration and verification ↗ · Rheem
- Richmond water heaters FAQ ↗ · Richmond / Rheem
- Rheem to make G.E. water heaters (June 1999) ↗ · Supply House Times
- A.O. Smith recalls residential water heaters (CPSC recall 19-029, 2018) ↗ · Consumer Reports
- Split heat pump water heater warranty (2025) ↗ · A.O. Smith
- Warranty verification ↗ · A.O. Smith
- Form 10-K, fiscal 2025 ↗ · A. O. Smith Corporation, via SEC EDGAR
- Warranty Center and FAQs ↗ · Bradford White
- Serial number date code reference ↗ · Bradford White
- Technical bulletin TB-179 (serial number label) ↗ · Rinnai
- TB-074: condensing water heater warranty ↗ · Rinnai
- Recall RA-68362: Navien propane conversion kit (2018) ↗ · Health Canada
- NHW tankless water heater limited warranty ↗ · Navien
- Where to find your model number ↗ · Noritz
- When should you replace your water heater? (2024) ↗ · ENERGY STAR
- Cost of installing a heat pump water heater (2024) ↗ · ENERGY STAR
- Water heater lifespan: when to repair vs. replace (March 2026) ↗ · Rheem
- Tankless water heaters (archived June 2026) ↗ · U.S. Department of Energy, Energy Saver
- Water heater serial number decoder ↗ · Energy Trust of Oregon
- Water heater dating chart ↗ · InterNACHI
- Water heater age pages by brand (2023–2025) ↗ · Building Intelligence Center