How Old Is My Furnace or AC?

Where to find the serial number

Every furnace, air conditioner and heat pump carries a rating plate (sometimes called the data plate or nameplate). It lists the model number, which describes what the unit is, and the serial number, which identifies that one unit and, for most brands, when it was built. Use the serial number, not the model number.

How each brand writes the date

There is no industry standard. Some brands put the week first, some the year, some use letters for months. These are the current formats for the brands we see most in Denver-area homes. Orange is the year, blue is the week or month.

What your unit’s age tells you

• Built before 2010 (AC or heat pump): it almost certainly uses R-22. A leak or compressor repair can be expensive because the refrigerant is now recycled supply only. That is often the tipping point toward replacement.
• Built 2010–2024: most likely R-410A. Parts and refrigerant are still widely available. New systems sold now use R-454B or R-32, so a matching indoor coil matters if only the outdoor unit is replaced.
• Furnace older than 15 years: ENERGY STAR suggests weighing replacement at this point. In Colorado, also have the altitude setup and the venting checked, since the furnace may have been derated (or not) when it was installed. See our altitude guide.
• AC or heat pump older than 10 years: ENERGY STAR’s replacement guideline. A newer cold-climate heat pump can also qualify for Colorado incentives; see rebates and tax credits.

Know the age? Price the next step with the replacement cost calculator, or read furnace and AC replacement cost in Denver.

Questions

Where is the serial number on my furnace?

On the rating plate, a sticker usually inside the furnace on the side wall of the blower or burner compartment. Some models have it on the outside of the cabinet. You may need to remove the lower front door, which turns the furnace off through the door switch. Do not open sealed panels or reach into the burner area.

Where is the serial number on my AC or heat pump?

On the rating plate on the outdoor unit, usually on the side panel near the refrigerant line connections or the electrical cover. The indoor coil and air handler have their own plates and can be a different age.

Why does my unit show a date that seems too old or too new?

Two-digit years repeat every century, and some brands changed formats. The decoder assumes the most recent year that is not in the future. If the plate prints a “MFG date”, trust that over the decoded serial. Equipment can also sit in a warehouse for months before it is installed.

Is the manufacture date the same as the install date?

Not always. Most systems are installed within a few months of being built, but the permit record, the original invoice or a date the installer wrote inside the panel is the best proof of the install date.

My furnace is 20 years old but works fine. Should I replace it?

Age alone is not a reason to replace a furnace that passes a safety inspection. ENERGY STAR suggests considering replacement after about 15 years for a furnace and 10 years for an AC or heat pump, mainly because newer equipment is more efficient. Have the heat exchanger, venting and controls checked every year, and use our repair-or-replace calculator if a big repair comes up.

Does an older AC use R-22?

Systems built before 2010 usually use R-22. New equipment charged with R-22 could not be made from 2010, and U.S. production and import ended in 2020, so repairs that need refrigerant rely on recycled supply. Units built after 2010 typically use R-410A, and new systems are now moving to R-454B or R-32.

Sources (checked November 2026)
1. Building Intelligence Center — HVAC brand serial number index (Carrier, Trane, Goodman, Lennox, Rheem, York, Heil, Daikin pages)
2. HVACDirect — Goodman date of manufacture
3. PickHVAC — York serial number and month letters
4. ENERGY STAR — when to replace heating and cooling equipment
5. Carrier — R-22 phase-out dates
6. ACHR News — EPA and R-410A installation deadlines