How to read a Whirlpool water heater serial number
Whirlpool doesn’t build its own water heaters. They’re made by American Water Heater, part of the A.O. Smith group, and use American’s date code [2][3][4]:
- Digits 1–2: the year (11 = 2011, 97 = 1997).
- Digits 3–4: the week of the year, 01 to 52 (occasionally 53).
- The rest is a production number and doesn’t affect the date.
11 04 T403904 → 2011, week 4 → late January 2011
The Building Intelligence Center gives the same reading with its own Whirlpool examples [1].
Turning the week into a month
The serial gives a week, not a month. The decoder shows the month that week falls in; this table is a quick guide. Week boundaries shift by a day or two from year to year, so a week near the start or end of a month can land in the neighbouring month.
| Weeks | Month |
|---|---|
| 01–04 | January |
| 05–08 | February |
| 09–13 | March |
| 14–17 | April |
| 18–22 | May |
| 23–26 | June |
| 27–30 | July |
| 31–35 | August |
| 36–39 | September |
| 40–43 | October |
| 44–48 | November |
| 49–52 | December |
Worked examples
| Serial | How it reads | Made | Example from |
|---|---|---|---|
1104T403904 | 11 = year ’11; 04 = week 4 of the year | Week 4 of 2011 (around January) | Building Intelligence Center |
0128104380 | 01 = year ’01; 28 = week 28 of the year | Week 28 of 2001 (around July) | Building Intelligence Center |
9746123456 | 97 = year ’97; 46 = week 46 of the yearAmerican-family example 9746****** (46th week of 1997). | Week 46 of 1997 (around November) | Energy Trust of Oregon |
Where to find the serial number
On the rating label on the tank jacket. Make sure you copy the serial, not the model number. The serial is the one that starts with four digits.
Common questions
Who makes Whirlpool water heaters?
American Water Heater, which is why the date code is American’s [2][3].
How old is a Whirlpool water heater with serial 0128…?
01 is the year 2001 and 28 is the 28th week, so it was built in mid-July 2001.
Can one Whirlpool serial mean two different years?
Not in practice. The year is written with two digits, so the same code would only come round again after 100 years. The decoder still checks that the date isn’t in the future.
Is this when the water heater was installed?
No. It’s the week it was built. It went into the house some time later.
Not affiliated with Whirlpool or American Water Heater. Brand names are used only to say which serials this decoder reads.
Sources
- Building Intelligence Center: Whirlpool Water Heater AgeUsed for: Year + week first.
- Energy Trust of Oregon: Serial Number Decoder: Water Heater (PDF)Used for: Year + week first.
- InterNACHI (International Association of Certified Home Inspectors): InterNACHI Water Heater Dating ChartUsed for: Year + week first.
- Honest Home Inspections, LLC (hosted by InspectAPedia): How to determine Water Heater and Furnace Age (PDF, last updated 2009-01-06)Used for: Year + week first.