Reading the Labels on Your Furnace and Air Conditioner

Why this matters

When your heating or cooling stops working, the first call to a contractor goes much better if it starts with facts. "It's a three-ton system on R-410A, the furnace is an 80,000 Btu gas unit, and both were made in 2018" tells the technician what parts and refrigerant to bring, whether the equipment is likely still under warranty, and roughly what conversation is coming. "It's the one in the garage, I think it's pretty old" tells them nothing and often means an extra trip.

Every furnace, air handler and outdoor unit carries a nameplate (a rating label) that holds those facts. This card shows you where to find them, how to read the important ones, and how to photograph them so a contractor can read them too.

Where the labels are

Outdoor unit (the air conditioner condenser or heat pump). The nameplate is usually on a side or back panel, often near the corner where the electrical lines come in. You can read it from outside the unit. Do not remove any panel, and keep hands and tools away from the fan grille on top.

Furnace or air handler (the indoor unit). The nameplate is often on the side of the cabinet or on the inside of the lower door. If you can see it without removing anything, photograph it. If the only way to see it is to take a door off, leave that to the technician. A gas furnace should never run with its doors off, and the upper door covers the burners.

Indoor coil. On a system with a separate cooling coil sitting on top of the furnace, the coil has its own small label. It is often on the coil's metal case, just above the furnace.

The yellow energy label. Newer outdoor units often still carry the yellow federal energy guide sticker showing efficiency. It may have faded or been removed.

Two nameplates, side by side

These are made-up examples. Your labels will have the same kinds of fields, laid out differently.

INDOOR: GAS FURNACE          OUTDOOR: AC CONDENSER
Model  GF80-3A-V             Model  CX4-036-K
Serial 1806xxxxxx            Serial 1807xxxxxx
Input  80,000 Btu/h          Volts  208/230 V, 1 ph
Output 64,000 Btu/h          MCA    18.0 A
Volts  115 V, 1 ph           MOCP   30 A max breaker
Temp rise  35 - 65 F         Refrigerant  R-410A
Gas    Natural               Factory charge 7 lb 4 oz
                             Compressor RLA 14.1

Model. Identifies the product line, and often hides the size. On many outdoor units, a group of digits in the model is the nominal cooling capacity in thousands of Btu per hour. In "CX4-036-K", the 036 means about 36,000 Btu per hour. Common size codes are 018, 024, 030, 036, 042, 048 and 060. One ton of cooling is 12,000 Btu per hour, so 036 is 36,000 divided by 12,000, which is 3 tons. Not every manufacturer puts the size there, and a few use other codes, so treat this as a strong clue rather than a certainty.

Serial. Identifies your unit. Many manufacturers encode the manufacture date in it; in these examples "1806" and "1807" could read as 2018, weeks 6 and 7, but the code differs by brand. See related: Finding Out How Old Your Home Equipment Is.

Input and output (furnace). Input is how much heat the burner uses; output is how much reaches your house. On the example, 64,000 divided by 80,000 is 0.80, so this furnace delivers about 80 percent of the fuel's heat. That tells you it is a standard-efficiency furnace that vents through a metal flue; high-efficiency furnaces deliver about 90 percent or more and usually vent through plastic pipe. The seasonal rating, called AFUE, is close to this figure but not the same number.

Volts. The furnace runs on ordinary 115-volt household power; the outdoor unit on 208/230-volt power from a double breaker. This matters to an electrician, not to you, except for one check below.

MCA and MOCP (outdoor unit). Minimum circuit ampacity is the smallest wire size the circuit can use, expressed in amps. Maximum overcurrent protection is the largest breaker or fuse allowed. The breaker for the outdoor unit should not be larger than the MOCP.

Refrigerant. The type of refrigerant the system is built for, and how much was charged at the factory. This is one of the most important facts on the label.

Temperature rise (furnace). The range the air should warm up by as it passes through the furnace. A technician measures this; you just need to know it is there.

Why the refrigerant line matters so much

The refrigerant type tells a contractor, and you, a lot about the system's age and what repairs will involve.

• R-22. Older systems, generally installed before about 2010. U.S. production and import of new R-22 ended in 2020, so service now relies on recovered and recycled supply. A leak on an R-22 system often turns into a replacement conversation rather than a repair.
• R-410A. The common refrigerant in systems built from about 2010 into the mid-2020s.
• Newer refrigerants such as R-454B or R-32. Under federal rules, most new home air conditioners and heat pumps made from 2025 on use refrigerants with lower global-warming impact. They are mildly flammable, so equipment and service practices are built around that.

Refrigerants cannot be mixed, and a system cannot be switched from one to another just by adding a different gas. Handling refrigerant requires EPA Section 608 certification, so refrigerant work is always for a licensed, certified technician.

Worked example: the phone call that starts with facts

A homeowner's air conditioner starts blowing warm air on a hot afternoon. Before calling, she spends five minutes with her phone at the two units.

What she photographs. The outdoor nameplate from a little way back, so the whole label is in frame, then a close-up of the model, serial and refrigerant lines. The furnace label on the side of the cabinet, same two shots. One wide photo of each unit in its spot. She turns off the flash and tilts the phone slightly so the plastic label does not glare.

What she reads off them. Outdoor unit: model CX4-036-K, so about 3 tons. Refrigerant R-410A. Serial begins 1807. Furnace: 80,000 Btu input, 64,000 output, natural gas, serial begins 1806.

One check she can make herself. At the panel, the double breaker labeled for the air conditioner has 30 on its handle. The label's MOCP is 30 amps. The breaker is not larger than the label allows. She does not reset it if it has tripped more than once, and does not remove the panel cover. See related: Reading Your Electrical Panel and Its Breakers.

The call. "My AC is blowing warm. The outdoor unit is model CX4-036-K, R-410A, serial starts 1807. The furnace is an 80,000 Btu gas unit, serial starts 1806. I have photos of both labels and can text them. The outdoor unit is running and the fan on top is spinning." The dispatcher can tell from that sentence that it is a 3-ton, R-410A system likely from 2018, possibly still inside a parts warranty, and the technician arrives with the right refrigerant and a likely list of parts.

What would change the call. If the label had said R-22, she could have expected the technician to talk about the cost of refrigerant and about replacement as well as repair, and she would want time to think before deciding. If the outdoor fan had been silent while the unit hummed, that detail would have mattered to the dispatcher too. If she smelled burning at either unit, she would have switched the system off at the thermostat and said so on the call.

The trap she avoided. Guessing the size from how big the box looks. Outdoor units of different tonnage and different efficiency come in similar cabinets, and a guess of "about 4 tons" sends the wrong parts.

Reading the efficiency sticker

The yellow energy label on newer outdoor units shows cooling efficiency, and on heat pumps heating efficiency too. Since 2023 these labels use the U.S. Department of Energy's updated ratings written as SEER2, EER2 and HSPF2, which come from a tougher test and give lower numbers than the older SEER, EER and HSPF for the same equipment. A SEER2 number and an old SEER number are not directly comparable, so when comparing two systems, compare like with like.

The efficiency a system actually reaches depends on the outdoor unit, the indoor coil and the furnace or air handler being a matched set. The certified rating for your exact combination is listed on an industry directory that your contractor can look up from the three model numbers.

When the labels do not agree

Sometimes the three labels tell slightly different stories, and that is worth mentioning to a contractor rather than worrying about.

• Different dates. An outdoor unit made in 2018 on top of a furnace made in 2009 usually means one piece was replaced and the other kept. That is common, but the older piece is closer to its own replacement, and the matched efficiency rating may not apply to the mix.
• Different sizes. If the indoor coil's label suggests a different size from the outdoor unit (for example, a 30 in the coil model next to a 036 outdoor unit), it may be a deliberate match the manufacturer allows, or it may be a mismatch. That is a question for the technician, not something to judge from the labels alone.
• A heat pump outdoors. If the outdoor label says heat pump, it heats as well as cools, and the indoor unit may be an electric air handler rather than a gas furnace. The label will list heating ratings as well as cooling.

Photographing labels well

• Whole label first, then close-ups. A close-up alone can cut off the field that mattered.
• Straight on, no flash glare. Tilt the phone a little if the label is shiny.
• One wide shot showing where the unit is, so a technician knows which unit the label came from.
• Clean it gently with a dry cloth if dust hides the print. Do not use solvents; they can wipe the ink off.
• File them. Put the photos in your house records with the install date and installer. See related: Your House Records File and What Goes In It.

References

• U.S. EPA guidance on refrigerant phaseouts and Section 608 technician certification
• U.S. Department of Energy consumer guidance on air conditioner and furnace efficiency ratings
• See related: Reading a Nameplate: What It Tells You
• See related: Finding Out How Old Your Home Equipment Is
• See related: When to Stop and Call a Licensed Pro Around the House