Rinnai water heater age by serial number
The serial number is on the label on the left side panel of the heater. On a Rinnai tankless water heater built since late 2009, the first letter of the serial is the year and the second letter is the month.
Decode a Rinnai serial number
How to read a Rinnai serial number
Rinnai has used 2 serial formats. Find the one that matches the shape of your serial.
Year letter and month letter
The first letter is the year, starting with A for 2009. The second letter is the month, A for January through M for December with the letter I left out.
Shape: two letters, a period, two letters, a dash and six digits.
NK.CA-129326 reads as October 2021.
Year 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
Month 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
Year letters after N, for units built in 2022 or later, are given by only one reference and are left out of the decoder until a second source confirms them.
Year and month, first four digits
The first two digits are the year and the next two are the month.
Shape: eight to ten digits. Some plates print a period after the first two digits and a dash before the last six.
04.03-102521 reads as March 2004.
Where to find the serial number
The serial is on the label on the left side panel of the tankless heater.
If the serial number does not decode
- Plates from before 2009 often print the manufacture month and year beside the serial number.
- The manufacturer can confirm the date from the serial: Rinnai registration, warranty or serial lookup.
What the age tells you
| Equipment | Typical service life |
|---|---|
| Tank water heater | 10 to 15 years |
| Tankless water heater | about 20 years |
About Rinnai
Rinnai Corporation of Japan sold its first tankless water heater in North America in 1999. Its US arm is Rinnai America in Peachtree City, Georgia. Rinnai also built tankless units sold under the Bradford White name, and those carry Rinnai serial numbers.
Questions and answers
Which characters in a Rinnai serial number show the date?
The first letter is the year, starting with A for 2009. The second letter is the month, A for January through M for December with the letter I left out. This applies to units built since late 2009.
Why does my Rinnai serial number look different?
Rinnai has used 2 serial formats: year letter and month letter (built since late 2009); year and month, first four digits (built 1999 to 2009). The decoder tries each one.
Sources
- Building Intelligence Center: Rinnai water heater age (independent reference): https://www.building-center.org/rinnai-water-heater-age/
- McGarry and Madsen Inspection: age of a Rinnai water heater from the serial number (independent reference): https://www.howtolookatahouse.com/Blog/Entries/2018/8/how-do-i-tell-the-age-of-a-rinnai-water-heater-from-the-serial-number.html
- TanklessHelp: Rinnai tankless water heater age (independent reference): https://www.tanklesshelp.com/rinnai-tankless-water-heater-age-know-how-old-it-is/
Formats last checked against these sources on October 5, 2026. Found a serial that does not fit? Send a correction. How formats are verified: method and sources.