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How to Find the Tonnage of an AC Unit From the Model Number

SignedBid Team11 min read
hvacdiagnostics

One ton of air conditioning is 12,000 Btu/h of heat removal: the rate of a short ton of ice melting over 24 hours. The tonnage of a specific unit is encoded in the model number printed on the outdoor unit's data plate, not the serial number, as a two- or three-digit capacity code. For most brands, dividing that code by 12 gives the right answer. For a documented set of Trane, American Standard, Goodman, Amana, and newer Lennox codes, that same division returns a size no manufacturer builds, and the brand's own published table has to be read instead.

Where to Find the Model Number

The tonnage lives on the outdoor unit, the condenser or heat pump sitting on a pad or bracket outside the house, not on the indoor coil, air handler, or furnace. Open the service panel or look at the side of the cabinet for a metal or vinyl data plate. It carries two separate identifiers that are easy to confuse: a model number, which describes what the unit is (capacity, efficiency tier, and often refrigerant type), and a serial number, which only records when it was manufactured. The serial number cannot tell you tonnage under any brand's scheme; only the model number can.

The Basic Rule: What the Capacity Code Means

Most residential AC and heat pump model numbers embed nominal cooling capacity as a code equal to the Btu/h rating divided by 1,000. Find a two- or three-digit run in the model number (usually flanked by letters on both sides) and divide it by 12 to convert to tons:

  • 018 = 1.5 tons (18,000 Btu/h)
  • 024 = 2 tons (24,000 Btu/h)
  • 030 = 2.5 tons (30,000 Btu/h)
  • 036 = 3 tons (36,000 Btu/h)
  • 042 = 3.5 tons (42,000 Btu/h)
  • 048 = 4 tons (48,000 Btu/h)
  • 060 = 5 tons (60,000 Btu/h)

This ladder covers the standard residential range, and it's the correct method for a large share of the equipment on the market: Goodman's and Amana's own light-commercial and package-unit lines use it directly, as do most Rheem, Ruud, and York residential condensers. The shortcut fails only on specific, documented code families, and those families happen to include some of the most common residential brands in the country. Two things break it: a manufacturer whose published table doesn't match naive Btu-per-1,000 arithmetic, and a model number where the capacity code isn't the first plausible two-digit run you find.

Why "Divide by 12" Breaks on Trane and American Standard

Trane and American Standard, sister brands under the same manufacturer, print a capacity code table that doesn't follow the naive 1,000-Btu ladder above. Their published codes are 19, 25, 31, 37, 43, 49, and 61 for 1.5 through 5 tons, each one digit higher than the naive code it corresponds to.

Take a Trane condenser reading 4TTR6037J1000AA on its data plate. The capacity field is 037. Divide that by 12 the naive way and you get 3.08 tons, a size nobody manufactures, which is the tell that this code isn't meant to be divided at all. Trane's own nomenclature table maps 037 directly to a 3 ton, 36,000 Btu/h unit. The published table governs, not the arithmetic.

Goodman and Amana Use the Same Shifted Codes

Goodman and Amana, also sister brands under Daikin, apply the identical off-by-one pattern to their split-system condensers and heat pumps: 019, 025, 031, 037, and 043 correspond to 1.5, 2, 2.5, 3, and 3.5 tons. Every one of these codes sits exactly 1,000 Btu/h away from the number naive division would need to see for the arithmetic to work cleanly. A Goodman GSX140301 divides its 030 code straight through to 2.5 tons under the naive ladder, because 030 happens to fall in the range where Goodman's shifted table and the naive table agree. A GSX160371 does not: its code is 037, and only Goodman's published table (037 = 3 tons) gives the right answer, not 037 ÷ 12.

Lennox's Newer Codes Break the Pattern the Other Direction

Lennox's current R-454B refrigerant product line (its XC, EL, and SL series, introduced alongside the 2025 refrigerant transition) carries capacity codes of 041, 047, and 059 for 3.5, 4, and 5 tons. These sit one increment below the naive ladder (042, 048, 060) rather than above it, the opposite direction from Trane's and Goodman's shift. There's no single rule that predicts which direction a manufacturer's table will deviate. The only reliable method is checking the specific brand's published code against the number on the plate, not assuming a universal offset.

Carrier's Leading "24" Prefix Trap: Why Position Matters

The most common way to misread a capacity code isn't a wrong digit: it's reading the right digits from the wrong position. Carrier's residential outdoor units open their model numbers with a two-digit product-family prefix, not the capacity code: 24 identifies an AC condenser, 25 identifies a heat pump, and 58 or 59 identifies a gas furnace. The capacity field comes later in the string, after that family group and a SEER-class digit.

A Carrier condenser reading 24ACC636A003 shows why position matters. Scan left to right for the first two-digit number and you land on 24; divide that by 12 and you get 2 tons, which is wrong. The 24 is Carrier's product-family prefix, identifying this as an AC condenser, not a capacity code. The actual capacity field is 36, positioned after the ACC family letters and the SEER-class digit. 36 divided by 12 is 3 tons, or 36,000 Btu/h, the unit's real nominal capacity. A left-to-right scan that doesn't know Carrier's field order will read this unit one size smaller than it actually is.

Bryant and Payne are Carrier's sister brands, sold through separate dealer networks but built on the same corporate nomenclature. The same field order and the same naive-ladder capacity codes (018 through 060) apply to their condensers as well. A Bryant or Payne model number reads exactly like a Carrier one once you identify and skip the family prefix.

Ductless Mini-Splits: Mitsubishi, Fujitsu, LG, and MrCool

Ductless equipment (the wall-mounted or ceiling-cassette indoor heads paired with an outdoor compressor) is specified and sold by Btu class rather than by tonnage, though the underlying math is identical. Standard classes are 09, 12, 15, 18, 24, 30, and 36, corresponding to 9,000 through 36,000 Btu/h.

A Mitsubishi indoor head reading MSZ-GL12NA follows the standard convention. The capacity code is 12, giving 12,000 Btu/h, or one ton. Fujitsu and MrCool use the same logic: their capacity codes are also Btu/h in thousands, embedded directly in the model string.

LG breaks the pattern outright, and it's the exception worth knowing before you convert one wrong. LG's mini-split model numbers encode capacity in hundreds of Btu/h, not thousands. A model reading LSU120HSV5 carries the code 120, and 120 × 100 = 12,000 Btu/h, one ton, the same capacity as the Mitsubishi example above. Read the LG code the way you'd read every other brand's, dividing 120 by 12, and you'd land on 10 tons: ten times the unit's actual capacity. That misread is the costliest kind on a mini-split nameplate, because it isn't a rounding difference; it's an order of magnitude off.

Why a Furnace Model Number Never Gives You a Tonnage

A furnace has no tonnage, because tonnage is a unit of cooling capacity and a furnace produces heat, not cooling. That doesn't stop furnace model numbers from carrying a capacity-looking code in the same two- or three-digit format used for AC condensers, which is exactly why this is the most common misread on this subject.

A furnace's code encodes heating input, in thousands of Btu/h of gas consumed, not cooling capacity in tons. A Goodman furnace model reading GMVC960603BN carries the code 060. Read as an AC condenser code, 060 would mean 5 tons of cooling; on this furnace, it means 60,000 Btu/h of gas input. Carrier marks its own furnaces the same collision-prone way: the 58 and 59 model prefixes identify a gas furnace rather than a condenser, but the digits that follow can still land on a code like 060 that means something entirely different depending on which type of equipment it's printed on. Before converting any code to tons, confirm you're reading an outdoor condenser or heat pump model number, not a furnace or air handler.

Which Unit to Decode: Outdoor or Indoor?

Decode the outdoor unit: the condenser or heat pump. Cooling capacity is set there, and the capacity actually delivered by the installed system depends on the AHRI-certified combination of that outdoor unit with a specific indoor coil and blower, a matched-pair rating that lives in AHRI's own directory rather than on either component's model number alone. An indoor air handler or evaporator coil carries its own capacity code describing that component. Reading it in isolation tells you about the coil, not the system's actual delivered tonnage, which matters most on older systems where the indoor and outdoor halves may have been mismatched somewhere in the equipment's repair history.

A Tonnage Code Isn't a Sizing Method

Reading an existing unit's tonnage off its model number and figuring out what tonnage a house needs are two different questions. This article only answers the first one. The commonly repeated shortcut for the second question (floor area divided by a fixed ratio, often written as "500 square feet per ton") has no authoritative table behind it, and published criticism of the practice puts the resulting oversizing error at 40 to 100 percent. An oversized system short-cycles, removes less humidity per run, and wears out its compressor faster than a correctly sized one. The method the building code and most rebate programs actually recognize is an ACCA Manual J load calculation, which accounts for insulation, window orientation, air infiltration, and internal heat gains. No square-footage ratio captures those inputs. For the full argument and the sourcing behind that 40-to-100-percent figure, see our explainer on why square-footage HVAC sizing rules get it wrong and what a real load calculation checks instead.

What If the Model Number Doesn't Match Any of These Patterns?

Not every model number decodes cleanly by eye, especially on older or less common brands. If no documented brand pattern applies, the safer move is scanning the string for a standard capacity code and accepting a match only when exactly one plausible code is present. A model number containing two different two-digit runs that could each plausibly be the capacity code should be treated as ambiguous, not guessed at. A confidently stated wrong tonnage is worse for a quote or a purchase decision than admitting the number isn't readable from the string alone; in that case, the manufacturer's model lookup tool or a call to their support line settles it faster than guessing.

Do Heat Pumps Use the Same Capacity Codes as Air Conditioners?

Yes. A heat pump moves heat in both directions but is rated for cooling capacity the same way an air conditioner is, and its model number carries the identical capacity code logic, including the same brand-specific exceptions. A Trane heat pump reads the code the same way a Trane AC condenser does: 037 means 3 tons on a 4TWR6037 heat pump exactly as it does on a 4TTR6037 air conditioner, because both product lines draw from the same published nomenclature table. The letters that follow the product-series digits tell you which product type you're looking at (Trane uses TTR/TTZ for straight air conditioners and TWR/TWZ for heat pumps), but the capacity field itself doesn't change meaning between the two.

The Easy Way

Manually cross-referencing which brand's table applies, which direction it deviates from the naive ladder, and where the capacity field sits in the string works, but it's slow to redo every time a data plate is in front of you. Our AC tonnage calculator handles the lookup directly: paste the model number, and it matches the brand's documented nomenclature (covering Trane and American Standard, Goodman and Amana, Lennox, Carrier, Bryant and Payne, and the ductless mini-split brands above), reads the capacity field from the correct position, and flags furnace model numbers instead of misreading them as tonnage. Once you know the tonnage of the equipment on the wall, our SEER2 savings calculator compares its running cost against a modern replacement at the same capacity.