What Is a Ton of Refrigeration? Tons, BTU and kW of Cooling Made Simple

Ask a contractor how big your chiller is and the answer comes back in a strange unit: "That's a 300-ton machine." Three hundred tons of what? Nothing about the chiller weighs three hundred tons, and it isn't lifting anything. Yet almost every piece of cooling equipment in Malaysia — chillers, packaged units, even the split unit on your office wall — is sized in this odd currency of "tons."

This part clears it up. By the end you'll know exactly what a ton of refrigeration is, how it connects to the two other units you'll meet everywhere (BTU and kW), and how to move between them without getting lost. Most importantly, you'll learn to spot the single most common mistake people make with cooling numbers: confusing the cooling a machine delivers with the electricity it consumes. They are both measured in kW, and mixing them up will wreck every calculation you try to do.

A "ton" is a rate of cooling, not a weight

The unit is a leftover from the days before mechanical refrigeration, when buildings were cooled with actual blocks of ice. Engineers needed a way to describe how much cooling a new machine could do, so they compared it to something everyone already understood: melting ice.

Here is the exact idea. Take one ton of ice — 2,000 pounds of it — sitting at melting temperature. To melt all of it into water over 24 hours, you have to pull a specific amount of heat out of your surroundings and into the ice. A machine that can remove heat at that same steady rate is doing "one ton" of refrigeration.

Notice the words rate and steady. A ton of refrigeration is not an amount of cooling you have in storage. It is a speed — how fast a machine can remove heat, continuously, for as long as it runs. This is the same distinction as the difference between the litres in your water tank and the litres-per-minute coming out of the tap. A ton is a litres-per-minute kind of number: it tells you the flow of heat being carried away, not a quantity sitting still.

Get this one idea straight and everything else falls into place. Cooling capacity is always a rate.

BTU: the unit of heat itself

To put a number on that rate, we first need a unit for heat. In the imperial system that unit is the BTU, the British Thermal Unit.

One BTU is the amount of heat you must add to raise one pound of water by one degree Fahrenheit. That's it — a small, fixed parcel of thermal energy. Heating a pot of water on the stove adds BTUs to it. Cooling a room removes BTUs from it. A BTU is a quantity of heat, in the same family as a joule or a calorie.

By itself, a BTU says nothing about speed. Removing 100,000 BTU in one minute and removing the same 100,000 BTU spread over a whole day are two completely different jobs, even though the total heat is identical. To describe cooling you always need the rate — heat per unit of time. That's why cooling capacity is written as BTU/h: BTUs removed per hour. The "/h" is not a detail you can drop. It's the difference between a quantity and a rate, and it's the whole point.

Putting a number on the ton

Now we can nail the ton down precisely. Melting that 2,000-pound block of ice takes about 144 BTU for every pound. So:

- 2,000 lb × 144 BTU/lb = 288,000 BTU to melt the whole ton
- Spread evenly over 24 hours: 288,000 ÷ 24 = 12,000 BTU/h

That's the definition, and it's worth memorising because it appears constantly:

1 ton of refrigeration (RT) = 12,000 BTU/h of cooling.

So a 300-ton chiller can remove 300 × 12,000 = 3,600,000 BTU of heat every hour. The room-sized split unit rated at "24,000 BTU/h" is a 2-ton machine (24,000 ÷ 12,000). Once you know that one machine is quoted in tons and the other in BTU/h, you can see they're speaking the same language — just with different-sized words.

Bringing it into kW: the metric that matters here

Imperial units are fine for reading a nameplate, but Malaysia runs on the metric system, and — crucially — your electricity bill is metric. To connect cooling to energy and cost, we convert BTU/h into kilowatts.

The conversion is fixed:

1 RT = 12,000 BTU/h = 3.517 kW of cooling.

That 3.517 kW is the rate at which the machine removes heat, now expressed in metric power units. (Recall from the Electricity Fundamentals series that 1 kWh equals 3.6 MJ of energy; a kW is simply that energy delivered per unit of time. Heat obeys the same bookkeeping as electricity — it's all just energy moving.)

So our 300-ton chiller removes heat at 300 × 3.517 = 1,055 kW of cooling. A 2-ton split unit removes about 7 kW of cooling. These are real, physical rates of heat removal, and they're the numbers you'd use to check whether a machine is big enough for a space.

The kW trap — and how to never fall into it

Here is where nearly everyone slips, so read this section twice.

The number we just calculated — 3.517 kW per ton — is kW of cooling coming out of the machine. It is the useful work: heat carried away from your building.

But a chiller also consumes electricity to do that work, and electricity is measured in kW too. The compressor motor might draw, say, 0.6 kW of electrical power for every ton of cooling it produces. That's kW of electricity going in.

Two completely different quantities, same three letters. If you don't say which one you mean, "kW" is ambiguous and any calculation built on it is worthless.

The rule of thumb: the kW of cooling out is always much larger than the kW of electricity in. That's the whole magic of a chiller — it doesn't make cold, it moves heat, and moving heat is far cheaper than the amount of heat you move. A good water-cooled chiller delivers roughly 3.5 kW of cooling for every 0.6 kW of electricity it draws. So whenever you see a cooling number that's several times bigger than you'd expect from a power bill, that's the cooling side. The smaller number is the electricity.

To keep them apart, engineers give the input side its own unit: kW per RT — the electrical kilowatts consumed for each ton of cooling produced. A chiller at 0.6 kW/RT draws 0.6 kW of electricity per ton. Lower is better, because you're getting the same cooling for less power.

The same relationship expressed as a single dimensionless number is the coefficient of performance (COP) — cooling out divided by electricity in:

COP = 3.517 ÷ (kW per RT)

Run the numbers and the picture is clear:

- 0.65 kW/RT → COP ≈ 5.4
- 0.60 kW/RT → COP ≈ 5.9
- 0.55 kW/RT → COP ≈ 6.4
- 0.50 kW/RT → COP ≈ 7.0 (excellent, for a water-cooled machine)

A COP of 6 means the chiller delivers six units of cooling for every one unit of electricity it eats. Air-cooled machines and small split units work harder for their cooling and sit higher on the kW/RT scale (often around 1.0 kW/RT, a COP near 3.5), which is why a room air-conditioner feels so much thirstier per ton than a central plant.

For split units and other small equipment, you'll also see Malaysia's Suruhanjaya Tenaga (Energy Commission) star rating on the label, based on the CSPF (Cooling Seasonal Performance Factor) — a seasonal efficiency measure suited to our steady tropical cooling load. More stars means more cooling per kilowatt across a realistic run of operating conditions. It's the same idea as COP, packaged for shoppers. (You may have seen "SEER" on imported units; that's the equivalent US rating — here, read the star label.) We'll take COP and kW/RT apart properly in the next part, on how efficiently a chiller actually turns electricity into cooling.

How the units are used in practice

In Malaysian building work, each unit has its own job:

- Sizing equipment: tons (RT). Chillers and packaged units are specified and bought in tons — a "500 RT plant," a "5 RT split system."
- Nameplates and small units: BTU/h. Wall and cassette units are advertised as 9,000, 12,000, 18,000, 24,000 BTU/h. Divide by 12,000 to get tons.
- Cooling capacity in metric: kW of cooling. Used when engineers cross-check loads against a building's heat gain.
- Electricity consumed: kW (power) and kWh (energy). This is what your meter records and what TNB bills.

Keep those four straight and the paperwork stops being intimidating.

A worked example, start to finish

Suppose your building runs a 100 RT water-cooled chiller measured at 0.6 kW/RT.

- Cooling delivered: 100 × 3.517 = 351.7 kW of cooling (this must match the building's cooling need)
- Electricity drawn: 100 × 0.6 = 60 kW of electrical power
- Efficiency: COP = 3.517 ÷ 0.6 ≈ 5.9
- Run it flat out for one hour and it uses 60 kW × 1 h = 60 kWh of energy — that's the part that lands on the bill.

Notice how cleanly the two kW numbers separate: 351.7 kW out, 60 kW in. Same unit, opposite sides of the machine. Anyone who reports "a 100-ton chiller uses 351 kW" has confused cooling with electricity by a factor of nearly six — a costly mistake if it ever finds its way into a budget.

That 60 kW of draw matters beyond the energy it uses. If your building is on a demand-metered (MD) tariff — the medium-voltage arrangement most commercial and industrial sites in Malaysia sit on — TNB also bills your peak power in kW. Under the RP4 tariff, that maximum-demand charge runs about RM89.27 to RM97.06 per kW each month, effective 1 July 2025. So the electrical side of a chiller shows up twice on the bill: once as energy (kWh) and again as demand (kW). If you'd like to see how a peak like this translates into ringgit, Cobler's maximum-demand calculator walks through it.

The one thing to remember

A ton of refrigeration is a rate of cooling — 12,000 BTU/h, or 3.517 kW of heat removed per hour. It describes what a machine delivers, never what it costs to run. The electricity it draws is a separate, smaller number, and the ratio between the two — kW/RT, or its cousin the COP — is where efficiency lives. Master that split and you can read any cooling spec sheet in the country.

From here the course gets practical. The next part turns these tons into a power bill by pulling apart kW/RT and COP in full, and the one after that follows the heat all the way from your rooms to the sky. If you want to start earlier in the story, the wider Learn hub lays out cooling from the ground up.