How old is my Day & Night furnace?
Serial number age decoder for Day & Night furnaces: 1 format era, 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: 4006A17330
- Day & Night furnace serial numbers in the 1980 to present format encode the year as digits 3-4 (2-digit year; century by context, 1980+) and the week as digits 1-2 (01-53) (source: building-center.org).
- Example: serial 4006A17330 decodes to week 40 of 2006.
- Day & Night's official lookup at dayandnightcomfort.com returns warranty / registration lookup.
Format eras
- 1980 to present VERIFIED
####A#####digits 3-4 (2-digit year; century by context, 1980+)
How to read the serial
1980 to present formatVERIFIED
Shape ####A##### · example 4006A17330 · confidence high
- Year
- digits 3-4 (2-digit year; century by context, 1980+)
- Week or month
- week = digits 1-2 (01-53)
- Plant
- letter at position 5 (plant/line code; table not published)
Example: serial 4006A17330 decodes to week 40 of 2006.
Listed under Carrier in the source; Day & Night is named in that format's family.
Where the data plate is on a furnace
Inside the furnace: remove the upper (burner) access door and look on the inside of the door, on the blower compartment wall, or on a sticker facing you at the burner deck.
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 Furnace at 15 to 25 years of expected service (nachi.org). That chart is a guideline, not a prediction for your unit.
Open the official Day & Night 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
- Historic Carrier/BDP brand, now marketed by ICP (icpusa.com our-brands). Styles 4006A17330 (WWYY-L, Carrier style 1) and 850304091 (YYMM 1980s). NOTE dayandnight.com is an unrelated company; the HVAC site is dayandnightcomfort.com. Building-center calls 4006A17330 'nine character' - it is ten.