Where to Find the Serial Number on a Furnace
On most furnaces the serial number is on a rating plate inside the lower blower compartment door. Here's where to look on each furnace layout, how to open it safely and how to turn the serial into an age.
By Suraj Jha · Updated 2026-11-01
Before you start: power off
- Find the furnace service switch, usually on the wall or the side of the furnace, and turn it off. If there isn’t one, switch off the furnace’s breaker.
- If it’s a gas furnace, you don’t need to shut off the gas just to read the label.
- Let the furnace cool for a few minutes if it was running.
Then remove the lower door, which covers the blower. It usually lifts up and out, or has two screws or clips.
Where the label is, by furnace layout
| Furnace layout | Where it’s usually installed | Where to look for the rating plate |
|---|---|---|
| Upflow (air goes up) | Basement, closet, utility room | Inside the lower blower door, on the left or right side wall |
| Downflow (air goes down) | Closets in homes with floor ducts; manufactured homes | Inside the upper door (the blower is on top), or on the inner side panel |
| Horizontal | Attics and crawl spaces | On the side of the cabinet facing the access panel; check both ends |
| Manufactured-home furnace | Hallway closet | Inside the lower front panel, often on the right-hand wall |
Many furnaces also have a second, smaller label on the outside of the cabinet with the model and serial, which is handy for attic furnaces you can’t easily open.
What you’re looking for
The rating plate lists:
- Model number: letters and digits describing the series, efficiency and input (for example
GMVC960804CNor59SC5A080S17). - Serial number: the unit’s unique number. On most brands it contains the build date.
- Input and output BTU, gas type, electrical ratings, and sometimes a printed manufacture date.
Reading the age from the serial
Each brand uses its own code:
| Brand | Date is in | Example |
|---|---|---|
| Carrier, Bryant, Payne | First 4 digits: week + year | 2406… = week 24, 2006 |
| Goodman, Amana, Daikin | First 4 digits: year + month | 0601… = Jan 2006 |
| Lennox, Armstrong | Digits 3–4 = year, then a month letter | 5806K… = Oct 2006 |
| Trane, American Standard | Depends on length: year + week | 11241… = week 24, 2011 |
| Rheem, Ruud | After the plant letter: week + year | W2912… = week 29, 2012 |
| York, Coleman, Luxaire | 2nd + 4th characters = year, 3rd = month | W1G7… = Jul 2017 |
| Heil, Tempstar | After the plant letter: year + week | E1423… = week 23, 2014 |
| Intertherm, Miller | Characters 4–5 = year, 6–7 = month | LMB0807… = Jul 2008 |
Or skip the decoding: the HVAC age lookup does it for you.
If there’s no label at all
- Installation paperwork and warranty registration usually record the model, serial and install date.
- Permits: furnace replacements often require a permit; your local building department may have the date.
- Home inspection reports from when you bought the house typically note the furnace’s age.
- The manufacturer can sometimes date a unit from the model number and other markings if you send photos.
Frequently asked questions
Where is the serial number on a furnace?
On the rating plate, usually inside the lower door that covers the blower. Some furnaces also have a copy of the label on the outside of the cabinet or inside the upper burner door.
Is it safe to open the furnace door?
Yes, if you switch off the power first using the service switch near the furnace (it looks like a light switch) or the breaker. Many furnaces have a door safety switch that cuts power when the panel is removed, but don't rely on it.
What's the difference between the model and serial number on a furnace?
The model number describes the furnace (series, efficiency, BTU input). The serial number identifies the individual unit and, for most brands, encodes the manufacture date.
The label is faded. What can I do?
Photograph it with your phone with the flash off and boost the contrast. Also check for a second label elsewhere on the cabinet, and look at the furnace's installation paperwork or warranty registration.
Next steps
Look up the age of your furnace and air conditioner
More about furnaces and boilers
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