Is your water heater making strange noises, or is the water taking forever to heat up? If you inherited an old unit or simply lost track of time, you might be relying on an appliance that is past its prime.
Water heaters do not last forever. Knowing the exact age of your unit is critical for maintenance and deciding when to budget for a replacement.
Every manufacturer hides this information differently. In this guide, we will show you exactly how to find and decode the serial number on your water heater so you are never left guessing.
Key Takeaways
- Locate the label: Find the manufacturer’s data plate on the side of the tank near the warning stickers.
- Decode the serial number: This string of digits and letters holds the secret to the manufacture date, though formats vary by brand.
- Consult the guide: Use our brand-specific breakdowns below to interpret codes for A.O. Smith, Rheem, Bradford White, and others.
- Plan for replacement: If your tank is over 10 years old, start planning for a new unit to avoid emergency leaks.
How to Determine Water Heater Age
Finding the age of a water heater is usually straightforward on modern units. Most recent models list a clear “Date of Manufacture” or “Mfg Date” right on the data plate.
However, older models force you to do some detective work. You must locate the serial number to unlock the production date.
Look for the rating plate on the side of the heater. This sticker lists the model number, serial number, and wattage. Once you have the serial number, you can decode the month and year of construction.
Since every manufacturer uses a unique pattern, we have compiled the specific formats for the leading brands below.
A.O. Smith
A.O. Smith uses a logical system that is easy to read.
For models made before 1997, the first four numbers represent the year and the week. The format appears as YYWWxxxxxx.
For models manufactured between 1997 and 2008, the system changes slightly. You will see a number followed by a letter ranging from ‘A’ to ‘M’ (skipping ‘I’). The letter represents the month (‘A’ is January), and the two following numbers indicate the year.
Current models often return to the basic numerical format or clearly state the date.
Included Brands
- A.O. Smith
- PermaGlas
- Glascote
Examples of Serial Numbers
- 9808: Built in 1998, week 08.
- F06: Built in June (F), 2006.
- 1617*: Built in 2016, week 17.
Rheem
Rheem protects its brands with a consistent coding style. For units made after 2000, the first four digits usually tell you the month and year.
In most cases, the first two digits are the month and the next two are the year.
However, Rheem sometimes flips the script. In some older models (or specific sub-brands), the date code sits in the middle of the serial number rather than at the start.
For vintage models made before 1999, Rheem used weeks instead of months.
Included Brands
- Rheem
- Richmond
- Ruud
- Vista Therm
- Lowe’s
- Montgomery Ward
- GE (often Rheem manufactured)
Examples of Serial Numbers
- 1110: November (11) of 2010 (10).
- 1298: Week 12 of 1998.
Bradford White
Bradford White relies on a letter-based system. The first letter represents the year, and the second letter signifies the month.
This system repeats every 20 years, so you will need to judge the condition of the heater to know which era it belongs to.
Year Decoder (1st Letter)
- S: 2018 or 1998
- P: 2017 or 1997
- N: 2016 or 1996
- M: 2015 or 1995
- L: 2014 or 1994
- K: 2013 or 1993
- J: 2012 or 1992
- H: 2011 or 1991
- G: 2010 or 1990
- F: 2009 or 1989
- E: 2008 or 1988
- D: 2007 or 1987
- C: 2006 or 1986
- B: 2005 or 1985
- A: 2004 or 1984
- Z: 2003 or 1983
- Y: 2002 or 1982
- X: 2001 or 1981
- W: 2000 or 1980
- T: 1999 or 1979
Month Decoder (2nd Letter)
- A: January
- B: February
- C: March
- D: April
- E: May
- F: June
- G: July
- H: August
- J: September
- K: October
- L: November
- M: December
Included Brands
- Bradford White
- Jetglas
Examples of Serial Numbers
- DG*: Built in July (G) of 2007 (D).
- NK*: Built in October (K) of 2016 (N) or 1996.
American Water Heaters
American Water Heaters became a subsidiary of A.O. Smith in 2001. Consequently, newer models use the standard A.O. Smith numbering system.
For older units, the logic varies. In the examples below, the first system places the year first (YY), followed by the week (WW). The second system uses a letter for the month and numbers for the year.
Included Brands
- American Water Heaters
- Whirlpool
- U.S. Craftmaster
- Environtemp
- Mor-Flo
- Polaris
Examples of Serial Numbers
- 9510: Built in 1995, week 10.
- E05: Built in May (E), 2005.
State Industries / Kenmore
State Industries manufactures heaters for many recognizable retail brands, including Kenmore. This can make the lookup confusing because they utilize multiple formats.
Format 1 uses numbers only: The first two digits are the year, and the next two are the week.
Format 2 uses a letter for the month (A, M) followed by the year.
Included Brands
- State
- Kenmore (Sears)
- Reliance
- Crosley
- Ace Hardware
Examples of Serial Numbers
- 1210*: Built in 2012, week 10.
- E03*: Built in May (E), 2003.
- E03*: Built in May (E), 2003 (ignore the prefix letter).
Lochinvar
Lochinvar uses a letter-based system similar to Bradford White. The first letter is the year, and the second letter is the month.
Year Decoder (1st Letter)
- N: 2016
- M: 2015
- L: 2014
- K: 2013
- J: 2012
- H: 2011
- G: 2010
- F: 2009
- E: 2008
- D: 2007
- C: 2006
- B: 2005
- A: 2004
Included Brands
- Lochinvar
- Knight
- Energy Saver
Examples of Serial Numbers
- PA*: Built in January (A), 1997 (P).
- XF*: Built in June (F), 2001 (X).
Navien
Navien tankless units use a more complex code. On newer models, look for a serial number where the 5th character is a letter, followed by numbers. The digits immediately following that letter usually indicate the year.
On older models, the year is simply the 5th, 6th, 7th, and 8th digits.
Examples of Serial Numbers
- C14X*: Production year is 2014.
- -2005-–: Production year is 2005.
Rinnai
Rinnai is a leader in tankless technology and uses two main patterns.
Newer models (post-2009) use a letter for the year (1st character) and a letter for the month (2nd character).
Older models (pre-2010) use numbers. The first two digits are the year, and the next two are the month.
Year Decoder (1st Letter)
- A: 2009
- B: 2010
- C: 2011
- D: 2012
- E: 2013
- F: 2014
- G: 2015
- H: 2016
- J: 2017
- K: 2018
- L: 2019
- M: 2020
- N: 2021
- P: 2022
- R: 2023
- S: 2024
Examples of Serial Numbers
- JB. –: Built in February (B), 2017 (J).
- 04.03-: Built in March (03), 2004 (04).
When Should You Replace Your Water Heater?
A well-maintained water heater is a workhorse, but it will not last forever. Most tank-style heaters have a lifespan of 10 to 15 years. Tankless units can last up to 20 years.
Watch out for these four signs that your unit is nearing the end of its life.
1. The Unit is Old
If your water heater is celebrating its 15th birthday, you are on borrowed time. Even if it seems to work fine, internal wear increases the risk of a sudden leak. Replacing it proactively is often cheaper than cleaning up a flooded basement.
2. Lukewarm Showers
Are you constantly fighting for hot water? If the water temperature fluctuates or runs out faster than it used to, sediment buildup has likely damaged the heating elements or the burner. This efficiency drop is a major red flag.
3. Rising Energy Bills
Heating water accounts for roughly 18% of your home energy usage (1). As a heater ages, it works harder to maintain temperature. If your utility bill spikes without an obvious cause, your aging water heater might be the culprit.
4. Rusty Water or Corrosion
Rust is the enemy of any water heater. If you see reddish-brown water coming from the hot tap, the inside of your tank is likely rusting away. Visible corrosion on the exterior or near the inlet/outlet pipes means a leak is imminent.
FAQs
How Old Is My Water Heater?
The easiest way to find the age is to check the information label on the side of the tank. Many manufacturers print the “Mfg Date” clearly. If you only see a serial number, use the brand-specific decoding guides in this article to translate that code into a manufacturing month and year.
What Is the Life Expectancy of a Water Heater?
A standard tank water heater typically lasts between 10 and 15 years. Tankless water heaters have a longer lifespan, often averaging 20 years. Hard water, high usage, and a lack of maintenance can significantly reduce these lifespans.
How Can I Make My Water Heater Last Longer?
Annual maintenance is key. Flush the tank once a year to remove sediment buildup that causes corrosion and inefficiency. Additionally, check the anode rod every 3 to 5 years and replace it if it is depleted; this sacrificial rod prevents the tank itself from rusting.
What Brand of Water Heater Is the Most Reliable?
Top-tier brands known for reliability include A.O. Smith, Rheem, and Bradford White. These manufacturers produce units for many other sub-brands (like Kenmore or Whirlpool) and generally offer consistent build quality and widely available parts.
Should I Proactively Replace the Water Heater?
Yes, if the unit is over 12 years old and located in an area where a leak would cause damage (like an attic or finished closet). Replacing it before it fails prevents water damage and allows you to shop for a deal rather than panic-buying during an emergency.
What Happens If You Don’t Replace a Water Heater?
Ignoring an aging water heater usually leads to tank failure. This can result in a massive leak that floods your home, causing thousands of dollars in water damage. At a minimum, you will eventually lose hot water completely, likely at the most inconvenient time.
Can I Look Up My Serial Number Online?
Yes, several major manufacturers offer online lookup tools. You can visit the official websites for brands like A.O. Smith, Rheem, and State Industries, enter your serial number into their warranty check tool, and it will confirm the manufacture date and warranty status.
In Summary
Water heaters are essential, but they have an expiration date. Once a unit passes the 10-year mark, the risk of leaks and failure rises significantly.
By finding the serial number and using the guides above, you can pinpoint exactly when your unit was built. Don’t wait for a cold shower to tell you it’s time for an upgrade; check your heater’s age today and plan ahead.
