Lochinvar water heater age by serial number
Lochinvar residential tank water heaters carry one of two date codes. Serials from 1979 to 2011 start with two letters, the year and the month: KJ-1000130 is September 1993. Newer serials start with four digits, the year and the week: 1142N012345 is week 42 of 2011. The decoder reads both with the tables in Lochinvar's warranty document.
Where the serial number is
The serial is on the rating plate of the tank, together with the model number, the capacity and the gas input or the electrical rating.
Two letters and a sequence (1979 to 2011)
The first letter is the year and the second the month. Lochinvar's year table runs from K for 1993 to Z for 2003 and from A for 2004 to J for 2012, skipping I, O, Q, R, U and V. Month letters go from A for January to M for December, without I. A dash and six or seven digits follow.
Year and week (2011 onward)
Newer residential tanks carry eleven characters: two digits for the year, two for the week, a letter for the plant and six digits of sequence. Lochinvar's example 1142N012345 was built in week 42 of 2011, which falls in October. Lochinvar has been part of A. O. Smith since August 2011, but the layout is Lochinvar's own.
Years outside Lochinvar's table
The letter code was in use from 1979, but the table covers only 1993 to 2012. Because the twenty letters repeat every twenty years, A to J also fit 1984 to 1992, and T to Z fit 1979 to 1983. The decoder shows those earlier years as a second reading and labels them as ours, not Lochinvar's.
Boilers and commercial heaters
The same warranty document also covers boilers and commercial water heaters, but those sections contradict themselves: one month table has I for September while its own example reads J as September, and one example's week does not match the digits. The decoder therefore stays with the residential tanks, where the document is consistent.
How to read the plate, step by step
- Look at the first two characters of the serial on the tank's rating plate.
- Two letters: read the first as the year from Lochinvar's table and the second as the month.
- Four digits followed by a letter: the digits are the year and the week, the letter is the plant.
- Where two years fit, the age of the installation usually makes the choice obvious.
Serial formats the decoder reads
| Format | How it is read |
|---|---|
| Lochinvar year letter + month letter (1979-2011) | Lochinvar residential tank, 1979-2011 layout: the first letter is the year and the second the month (A = January to M = December, I skipped), followed by 6 or 7 digits. |
| Lochinvar year + week (2011 on) | Lochinvar residential tank, 2011 onward: 11 characters; digits 1-2 are the year, digits 3-4 the week, the 5th character is the plant, then a 6-digit sequence. |
Worked examples
Each serial below is either printed in a source or built by us strictly by the source's rule (marked "by the rule"), and each is an automated test of the decoder. Readings that depend on today's date are as of October 27, 2026.
| Serial | Result | Why |
|---|---|---|
| KJ1000130from a source | September 1993Decoded | Lochinvar's example: K = 1993, J = September. |
| AB123456by the rule | February 1984 or February 2004Two possible dates | A = 2004 in Lochinvar's table; on the earlier cycle the same letter is 1984. |
| 1142N012345from a source | week 42 of 2011 (about October)Decoded | Lochinvar's example for the 2011 layout: week 42 of 2011. |
| A07H00123456by the rule | Not confirmed by the manufacturer | A boiler or commercial serial: left out because the source contradicts itself. |
| 0912N012345by the rule | Not confirmed by the manufacturer | The 11-character layout starts in 2011, so a year of 09 does not fit it. |
Edge cases and limits
- Year letters K to S give one year each (1993 to 1998); every other year letter gives two candidates.
- An eleven-character serial whose year is before 2011 does not fit the newer layout and is reported as not confirmed.
- Boiler and commercial serials, such as a month letter, two digits, a letter and eight digits, or a thirteen-digit number, are recognised and deliberately not decoded.
Questions
Is a Lochinvar water heater dated like an A. O. Smith?
No. Lochinvar kept its own layouts after the 2011 acquisition, so use this page for Lochinvar tanks.
Why are Lochinvar boilers not decoded?
Lochinvar's document gives boiler month tables and examples that disagree with each other; one example is called September although the table reads it as October. Until Lochinvar clarifies, a decoded date could be wrong, so we show none.
What does the letter in the middle of a newer serial mean?
It identifies the plant. It comes after the year and the week and does not change the date.
Related pages
- A. O. Smith family: A. O. Smith, Lochinvar's owner since 2011, dates its own brands differently.
- Bradford White: Bradford White uses a similar two-letter code on a 20-year cycle.
- All water heater brand families: Every brand family we decode, and the brands we do not decode yet with the reason.
- Where to find the data plate: Where the serial number sits on each type of equipment and how to copy it without mistakes.
- Service life estimates: What ENERGY STAR publishes about typical ages, and what kind of number each figure is.
Sources
Every rule on this page comes from the documents below, published by the manufacturer or a U.S. government agency. The date is when we last checked each one.
- Warranty information by serial number (WARR 100161789 Rev 18) Lochinvar, LLC. Checked .