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How old is my Day & Night furnace or AC?
Type the serial number from the Day & Night label to see when it was built. Day & Night units are built by ICP, a Carrier company, so the serials follow that company's format.
Example
- LPlant: L
- 00Year: 00 = 2000
- 41Week: 41 (around October)
Built Week 41 of 2000 (around October)
26 years old
Past typical life. Past the usual 15 to 25 year lifespan. Watch for rising gas bills, uneven heat, a yellow or flickering burner flame, rust or soot, and a carbon monoxide alarm.
How this was read
- The first letter, L, is the plant that built it.
- The next two digits, 00, are the year: 2000.
- The two digits after that, 41, are the week of the year.
Format: ICP plant letter, year and week. Sources: CPSC 2005 ICP packaged unit recall (serial format L004112345), ICP serial number nomenclature (Tempstar parts), InspectAPedia: Tempstar age, Building Intelligence Center: Heil, Inspector Handbook: Heil.
Reading a Day & Night serial number
Newer Day & Night units are built by ICP and start with a plant letter, then the year and the week.
Older units built by Carrier start with four digits and a letter. The checker tries both formats.
About Day & Night
- The name goes back to William J. Bailey’s Day & Night Solar Heater Company in Monrovia, California, which made solar water heaters in the 1910s.
- Day & Night joined Bryant and Payne in Affiliated Gas Equipment in 1949, and Carrier bought that company in 1955.
- When Carrier bought ICP in 1999, Day & Night was still a Carrier brand, separate from ICP. Today ICP builds it and sells it through independent distributors.
Sources: Solar Panels in the Roaring Twenties: A Day & Night Solar Heater Company Pamphlet, ca. 1921, Bryant Heating & Cooling: 100 Years of Doing What It Takes, Carrier and ICP: Distinct and Separate, Air Cold Supply's Northern California Region Wins Top Honors as Day & Night Distributor of the Year
ICP plant letter, year and week
Used about 1990 to today. Example: L004112345
Heil, Tempstar, Comfortmaker, Arcoaire, KeepRite and Day & Night serials start with a plant letter, then the year (2 digits), then the week (2 digits). L0041 means the 41st week of 2000. This is the reverse of Carrier’s week-then-year order.
Worked example: L004112345 was built Week 41 of 2000 (around October), so it is 26 years old as of October 2026.
Sources: CPSC 2005 ICP packaged unit recall (serial format L004112345), ICP serial number nomenclature (Tempstar parts), InspectAPedia: Tempstar age, Building Intelligence Center: Heil, Inspector Handbook: Heil
Heil-Quaker 1980s year digit and week
Used 1980 to 1989. Example: H55116328
Heil-Quaker units from the 1980s have a shorter serial that starts with H. The digit after the H is the year in the 1980s, and the next two digits are the week. H5511 means the 51st week of 1985.
Worked example: H55116328 was built Week 51 of 1985 (around December), so it is 40 years, 10 months old as of October 2026.
Sources: CPSC 2005 ICP packaged unit recall (serial format L004112345), ICP serial number nomenclature (Tempstar parts), InspectAPedia: Tempstar age, Building Intelligence Center: Heil, Inspector Handbook: Heil
Carrier week, year and plant letter
Used mid-1980s to today. Example: 3203E08663
Carrier, Bryant and Payne serials start with four digits and a letter. The first two digits are the week and the next two are the year. 3203E means the 32nd week of 2003, built at plant E.
Worked example: 3203E08663 was built Week 32 of 2003 (around August), so it is 23 years, 2 months old as of October 2026.
Sources: Bryant R-22 application and service manual, serial number page, Building Intelligence Center: Carrier, Building Intelligence Center: Bryant, Inspector Handbook: Carrier, Electrical Forensics: air conditioner date codes
Carrier 1980 to 1984 month letter and year digit
Used 1980 to 1984. Example: W4D14008
From 1980 to 1984 the serial starts with a month letter (M is January, O and U are skipped) and a year digit from 0 to 4. W4 means September 1984. Units built in Canada put the digit first.
Worked example: W4D14008 was built September 1984, so it is 42 years, 1 month old as of October 2026.
| Letter | Month |
|---|---|
| M | January |
| N | February |
| P | March |
| Q | April |
| R | May |
| S | June |
| T | July |
| V | August |
| W | September |
| X | October |
| Y | November |
| Z | December |
Sources: Bryant R-22 application and service manual, serial number page, Building Intelligence Center: Carrier, Building Intelligence Center: Bryant, Inspector Handbook: Carrier, Electrical Forensics: air conditioner date codes
Carrier 1980s year and month
Used late 1980s. Example: 850304091
Some 1980s Carrier, Bryant and Payne serials are 9 digits with no letter. The first two digits are the year and the next two are the month. 8503 means March 1985.
Worked example: 850304091 was built March 1985, so it is 41 years, 7 months old as of October 2026.
Sources: Bryant R-22 application and service manual, serial number page, Building Intelligence Center: Carrier, Building Intelligence Center: Bryant, Inspector Handbook: Carrier, Electrical Forensics: air conditioner date codes
Day & Night recalls
Recalls from the U.S. Consumer Product Safety Commission that name Day & Night. Whether a unit is included depends on its model and build date; the checker above flags matches.
| Year | Recall | Hazard |
|---|---|---|
| 1996 | Ducane-built oil furnaces sold under many brands | The heat exchanger can crack. |