Age helps you decide between repairing and replacing a heater. ENERGY STAR (opens in a new tab) suggests considering a replacement once a heater is more than 10 years old, before a failure forces a rushed choice; its savings estimates assume a 13-year lifespan. Real service life varies with water quality, maintenance and installation.
Read the serial number from the outside only. If you smell gas, see water near electrical equipment, or have an active leak, go to the safety checklist first.
Decode your serial number
How each brand dates its serial numbers
Each format comes from the manufacturer’s own documentation or from at least two independent references. Brands that share a factory share a format.
| Brand | Where to find the serial | How to read it | Example | Source |
|---|---|---|---|---|
| Rheem Rheem age guide | Rating label on the tank jacket; on tankless units, the label on the cabinet side; on heat-pump models, the label on the upper body. | MMYY… Optional letter prefix (R, RH, RN, RNG or RHNG), then two digits for the month and two for the year: MMYY. Example 1209D01234 = December 2009. | 1209D01234 | Rheem: how to locate and read your water heater serial number (opens in a new tab); also InspectAPedia: Rheem water heater age decoder (opens in a new tab) |
| Ruud | Rating label on the tank jacket. | [R/RH/RN/RNG/RHNG] MMYY… Optional letter prefix (R, RH, RN, RNG or RHNG), then two digits for the month and two for the year: MMYY. Example 1209D01234 = December 2009. | RHNG0804P000036 | Energy Trust of Oregon: water heater serial number decoder (PDF) (opens in a new tab); also InspectAPedia: Rheem water heater age decoder (opens in a new tab) |
| Richmond | Rating label on the tank jacket. | MMYY… Optional letter prefix (R, RH, RN, RNG or RHNG), then two digits for the month and two for the year: MMYY. Example 1209D01234 = December 2009. | 0794F12345 | Energy Trust of Oregon: water heater serial number decoder (PDF) (opens in a new tab); also InspectAPedia: Rheem water heater age decoder (opens in a new tab) |
| GE (tank heaters built by Rheem) | Rating label on the tank jacket. Use this only if the label names Rheem as the maker; GeoSpring heat-pump units were not built by Rheem and use a different code. | MMYY… Optional letter prefix (R, RH, RN, RNG or RHNG), then two digits for the month and two for the year: MMYY. Example 1209D01234 = December 2009. | 0806B17262 | Energy Trust of Oregon: water heater serial number decoder (PDF) (opens in a new tab); also InspectAPedia: Rheem water heater age decoder (opens in a new tab) |
| A. O. Smith A. O. Smith age guide | Rating plate on the side of the tank jacket. | YYWW… (2008+), YYMM… or month letter + YY (older) Current: the first four digits (after any single prefix letter) are YY then WW, year and production week; units built before 2008 use YY then MM, year and month. Older codes: a month letter A–M (no I) followed by a two-digit year, sometimes after one leading character. | 1210A002243 | A. O. Smith Canada: FAQs (reading the serial number) (opens in a new tab); also City of Palo Alto Utilities: check your water heater’s age (opens in a new tab) |
| State State age guide | Rating plate on the side of the tank jacket. | YYWW… (2008+), month letter + YY (older) Current: the first four digits (after any single prefix letter) are YY then WW, year and production week; units built before 2008 use YY then MM, year and month. Older codes: a month letter A–M (no I) followed by a two-digit year, sometimes after one leading character. | S1318F000046 | Energy Trust of Oregon: water heater serial number decoder (PDF) (opens in a new tab); also Building Intelligence Center: State water heater age (opens in a new tab) |
| Reliance | Rating plate on the side of the tank jacket. | YYWW… (2008+), month letter + YY (older) Current: the first four digits (after any single prefix letter) are YY then WW, year and production week; units built before 2008 use YY then MM, year and month. Older codes: a month letter A–M (no I) followed by a two-digit year, sometimes after one leading character. | 1211A018632 | Energy Trust of Oregon: water heater serial number decoder (PDF) (opens in a new tab); also Building Intelligence Center: Reliance water heater age (opens in a new tab) |
| American Water Heater American Water Heater age guide | Rating plate on the side of the tank jacket. | YYWW… The first two digits are the year and the next two the production week: YYWW. Example 9746… = week 46 of 1997. | 9746123456 | Energy Trust of Oregon: water heater serial number decoder (PDF) (opens in a new tab); also InspectAPedia: American water heater age (opens in a new tab) |
| U.S. Craftmaster | Rating plate on the side of the tank jacket. | YYWW… The first two digits are the year and the next two the production week: YYWW. Example 9746… = week 46 of 1997. | 043812019 | Energy Trust of Oregon: water heater serial number decoder (PDF) (opens in a new tab); also Building Intelligence Center: Craftmaster water heater age (opens in a new tab) |
| Whirlpool Whirlpool age guide | Rating plate on the side of the tank jacket. | YYWW… The first two digits are the year and the next two the production week: YYWW. Example 9746… = week 46 of 1997. | 1512A123456 | Energy Trust of Oregon: water heater serial number decoder (PDF) (opens in a new tab); also Waypoint Inspection: Whirlpool water heater age (opens in a new tab) |
| Bradford White Bradford White age guide | Rating plate attached to the water heater. | Year letter + month letter… First letter = year, second letter = month (A–M, no I). Year letters repeat every 20 years: A = 1984, 2004 or 2024; B = 1985, 2005 or 2025 … Z = 2003 or 2023. Letters I, O, Q, R, U and V are not used for years. | HK16433183 | Bradford White: my water heater information (opens in a new tab); also Energy Trust of Oregon: water heater serial number decoder (PDF) (opens in a new tab) |
| Rinnai Rinnai age guide | Rating label on the cabinet (side or bottom of the unit). | Year letter + month letter (2009+), YY.MM (older) Since 2009: first letter = year (A = 2009 … H = 2016, J = 2017 … N = 2021, P = 2022 (O on one 2022 model), R = 2023, S = 2024, T = 2025, W = 2026), second letter = month (A–M, no I). Before 2009: YY.MM, e.g. 04.03-… = March 2004. | BL.CA-051306 | Building Intelligence Center: Rinnai water heater age (opens in a new tab); also Parts Town: Rinnai serial number lookup (opens in a new tab) |
| Bosch | Gas tankless: rating label on the right side of the cover. Electric Tronic tankless: sticker on the bottom flange of the cover. | 4 characters + 3-character date code… The three characters after the first four are a date code that Bosch’s reference table maps to a month and year (for example 720 = April 2017, 173 = May 2021). Older “FD” serials use a different scheme. | 399A-720-000031-8733942691 | Bosch Home Comfort: serial number reference guide (PDF, 07.2026) (opens in a new tab) |
Brands without a confirmed date code
- Navien: Navien serials embed a production date in several layouts that we could not confirm against Navien documentation. Check the rating plate for a manufacture date or contact the manufacturer.
- Noritz: We found only one reference for a Noritz date format, which is not enough to rely on. Check the rating plate for a manufacture date or contact the manufacturer.
- Takagi: Newer Takagi units may use an A. O. Smith-style year/week code, but we could not confirm it with a second source; older serials are sequential and carry no date. Check the rating plate for a manufacture date or contact the manufacturer.
- Kenmore: Kenmore heaters were built by several manufacturers, so the format depends on who made yours. Check the rating plate for a manufacture date or contact the manufacturer.
- Suburban (RV): We could not confirm a Suburban serial date format. Check the rating plate for a manufacture date or contact the manufacturer.
- Atwood / Dometic (RV): We could not confirm an Atwood serial date format. Check the rating plate for a manufacture date or contact the manufacturer.
What the age means for repair or replacement
- A leaking tank means replacement, whatever its age. Water seeping from the tank body cannot be repaired, but many puddles come from fittings, a relief valve or condensation instead. A. O. Smith’s leak bulletin (opens in a new tab) and our leak guide help you tell them apart.
- Past about 10 years, plan ahead. ENERGY STAR (opens in a new tab) lists corrosion, leaks from joints or seams, rusty hot water, less hot water than before (often sediment) and rumbling or banging as signs that a heater is wearing out. On an older tank, these make replacement the safer choice. Typical service lives by type are in how long water heaters last.
- Younger heaters are usually worth diagnosing. Controls, elements, igniters and valves are replaceable parts, and the heater may still be under warranty. Give the serial number to the manufacturer to confirm coverage.
Next steps by symptom: no hot water · leaks · noises. Before calling a technician, write down what to tell them.
If the serial doesn’t decode
- Read the whole rating plate. Many labels print a manufacture date (“MFG. DATE” or similar) next to the serial number.
- Check the paperwork. The owner’s manual, the installer’s sticker or invoice, or the permit may record the installation date.
- Ask the manufacturer. Call or use the warranty lookup with the full model and serial number. Find the maker on the label, not just the store or RV brand. Our identification guide shows where to look.
Common questions
Where is the serial number on a water heater?
On the rating plate or label: usually on the side of a tank’s outer jacket, and on the side or bottom of a tankless cabinet. It is printed next to the model number. You never need to remove a cover to read it.
Why does the decoder show more than one year for Bradford White?
Bradford White reuses its year letters every 20 years, so “H” can mean 1991 or 2011. The decoder lists every year that isn’t in the future, newest first. Certification dates on the label, installation paperwork, or the heater’s condition usually tell you which one is right.
Is a 10-year-old water heater worn out?
Not necessarily. ENERGY STAR suggests considering a replacement once a heater is more than 10 years old, so that you choose one before it fails. Age is one factor; leaks, corrosion, rusty water and noise matter more.
My brand isn’t listed, or the serial won’t decode. What now?
Many rating plates print the manufacture date directly. If yours doesn’t, call the manufacturer with the full model and serial number. They can confirm the date and warranty status.