How old is my HTP water heater?
Serial number age decoder for HTP tank water heaters: 3 format eras, the decode rule in plain English, transcribed tables, and the official lookup.
Type the serial from the data plate, not the model number. Nothing is sent anywhere; the tables are in this page.
Format example: I21M28666
- HTP water heater serial numbers in the 1994 to 2011 format encode the year as letter 2 (4th char) (table below) and the month as letter 1 (A=Jan..L=Dec, I=Sep, 12 consecutive letters); day of month as digits 2-3 (source: htproducts.com).
- Example: serial I21M28666 decodes to September 2006.
- HTP water heater serial numbers in the 2011 to 2021 format encode the year as digits 5-6 (20YY) after dropping a 2-digit prefix when the serial is 16 digits and the month as digits 1-2, day as digits 3-4; the letter = production line (source: htproducts.com).
- Example: serial 112116E2054485 decodes to November 2016.
- HTP water heater serial numbers in the 2021 to present format encode the year as digits 10-11 (20YY) and the day of year = digits 12-14 (045 = Feb 14) (source: htproducts.com).
- Example: serial 3251200U4220450000188 decodes to day 45 of 2022.
- HTP's official lookup at htproducts.com returns warranty / registration lookup.
Format eras
- 2021 to present VERIFIED
#######A#############digits 10-11 (20YY) - 2011 to 2021 VERIFIED
######A#######digits 5-6 (20YY) after dropping a 2-digit prefix when the serial is 16 digits - 1994 to 2011 VERIFIED
A##A#####letter 2 (4th char): A=1994 B=1995 C=1996 D=1997 E=1998 F=1999 G=2000 H=2001 I=2002 J=2003
How to read the serial
2021 to present formatVERIFIED
Shape #######A############# · example 3251200U4220450000188 · confidence high
- Year
- digits 10-11 (20YY)
- Week or month
- day of year = digits 12-14 (045 = Feb 14)
- Plant
- chars 8-9 = Ariston factory code (e.g. U4, 02, 35)
Example: serial 3251200U4220450000188 decodes to day 45 of 2022.
2011 to 2021 formatVERIFIED
Shape ######A####### · example 112116E2054485 · confidence high
- Year
- digits 5-6 (20YY) after dropping a 2-digit prefix when the serial is 16 digits
- Week or month
- month = digits 1-2, day = digits 3-4; the letter = production line
Example: serial 112116E2054485 decodes to November 2016.
1994 to 2011 formatVERIFIED
Shape A##A##### · example I21M28666 · confidence high
- Year
- letter 2 (4th char): A=1994 B=1995 C=1996 D=1997 E=1998 F=1999 G=2000 H=2001 I=2002 J=2003 K=2004 L=2005 M=2006 N=2007 O=2008 P=2009 Q=2010 R=2011
- Week or month
- month = letter 1 (A=Jan..L=Dec, I=Sep, 12 consecutive letters); day of month = digits 2-3
| Year code | Year(s) |
|---|---|
| A | 1994 |
| B | 1995 |
| C | 1996 |
| D | 1997 |
| E | 1998 |
| F | 1999 |
| G | 2000 |
| H | 2001 |
| I | 2002 |
| J | 2003 |
| K | 2004 |
| L | 2005 |
| M | 2006 |
| N | 2007 |
| O | 2008 |
| P | 2009 |
| Q | 2010 |
| R | 2011 |
| Month code | Month |
|---|---|
| A | January |
| B | February |
| C | March |
| D | April |
| E | May |
| F | June |
| G | July |
| H | August |
| I | September |
| J | October |
| K | November |
| L | December |
Example: serial I21M28666 decodes to September 2006.
Where the data plate is on a water heater
The rating plate is a large label on the side of the tank near the top or beside the control. The serial is printed on it, often beside the model number and the ANSI standard line.
General guidance, not brand-specific: the owner's manual or the installer can point to the exact spot. See the data plate guide.
For scale only: the InterNACHI Standard Estimated Life Expectancy Chart for Homes lists Water Heater (conventional) at 6 to 12 years of expected service (nachi.org). That chart is a guideline, not a prediction for your unit.
Open the official HTP lookup takes serial number; returns warranty / registration lookup; URL verified live
This site is a reference built from published tables. The manufacturer's own lookup wins whenever the two disagree.
What we could not confirm
- Official PDF 'UnderstandSerialNumbers-2-2024.pdf' fully documents 3 HTP eras + 2 Ariston formats. Warranty Wizard (htp.my.site.com) takes a serial number; 'Find Serial Numbers' PDF gives label locations.