BTU, Tons and Cooling Capacity: Reading AC Ratings Correctly

Cooling capacity is quoted in BTU per hour or in kilowatts, and often summarised as a nominal tonnage. One refrigeration ton is roughly 12,000 BTU/hr, so an 18,000 BTU/hr unit is described as 1.5 ton.

Nominal versus rated

Nominal tonnage is a naming convention, not a measurement. The rated capacity on the datasheet is the number that was actually tested, and it is the figure to design with. Two units both sold as "2 ton" can differ measurably in tested output.

Why T1 and T3 matter here

Capacity is measured at a defined outdoor condition. T1 represents a moderate climate; T3 represents a high ambient temperature closer to Gulf summer conditions. The same machine always reports a lower capacity at T3 than at T1, because performance falls as outdoor temperature rises.

Comparing one manufacturer's T1 figure against another's T3 figure makes the T1 unit look stronger when it may not be. Always compare like with like, and where the equipment will run through a Gulf summer, size on the T3 figure.

Read the electrical data alongside

Rated input power, running current and starting current determine cable size and breaker selection. A unit chosen purely on cooling output can create an electrical problem downstream.

Other figures worth checking

• EER or SEER for running cost
• Airflow, which affects throw and room distribution
• Refrigerant type and charge
• Voltage, phase and frequency against the site supply

In short

Size the equipment on tested capacity at the condition it will actually work in, and confirm the electrical data before ordering.