Two kW Numbers, Only One Converts
Read a European mini-split's label and you will often see "3.5 kW" beside a second figure, "1.1 kW," and the instinct is to wonder which one is the BTU equivalent. The larger number — cooling capacity — is the one this conversion targets: 3.5 kW ≈ 12,000 BTU/h. The smaller number is the electrical input, the power the compressor actually draws, and it does not convert to BTU/h at this ratio. The gap between the two is the coefficient of performance, the same physics that lets a refrigerator move more heat than the electricity it consumes. Match capacity to capacity, input to input, and the confusion dissolves.
kW = BTU/h × 0.0002930710702
1 BTU/h = 0.0002930710702 kW
1 kW = 3,412.141633 BTU/h — the same constant, inverted.
Common AC Ratings, BTU/h and kW
| BTU/h rating | cooling capacity (kW) | typical electrical input (kW) |
|---|---|---|
| 9,000 BTU/h | 2.64 kW | ~0.8–1.0 kW |
| 12,000 BTU/h | 3.52 kW | ~1.0–1.5 kW |
| 18,000 BTU/h | 5.28 kW | ~1.8–2.2 kW |
| 24,000 BTU/h | 7.03 kW | ~2.4–3.0 kW |
| 36,000 BTU/h | 10.55 kW | ~3.6–4.5 kW |
The three-ton central system — 36,000 BTU/h — is a 10.55 kW machine in cooling terms but draws roughly a third of that as electricity. When you are sizing a generator, a breaker, or a solar array for an air conditioner, the number you need is the electrical input, and that is a watts to amps question at your supply voltage, not a BTU conversion.
Engineering Context
The same rate in watts rather than kilowatts is BTU/h to watts, and in the HVAC trade's own language it is BTU/h to ton (reverse at ton to BTU/h). For the energy dimension — total heat, not rate — use BTU to kWh or kWh to BTU. If the electrical input is the number in hand, kW to watts and kW to hp carry it into the circuit-design and motor worlds.
More: BTU/h to watts · BTU/h to ton · BTU to kWh · Energy Hub
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Frequently Asked Questions
How many kW is 12,000 BTU?
12,000 BTU/h is 3.517 kW of cooling. The 12,000 BTU/h rating — one ton of refrigeration — is 12,000 × 0.0002930710702 = 3.5169 kW of heat removed per hour. Note this is thermal power, not the electrical draw, which for an efficient unit is closer to 1.0 to 1.5 kW.
Is a 3.5 kW air conditioner the same as 12,000 BTU?
Yes, if both numbers are cooling capacity. A 3.5 kW unit and a 12,000 BTU/h unit are the same machine: 12,000 BTU/h equals 3.5169 kW exactly. The catch is that many spec sheets list two kW numbers — cooling capacity and electrical input — and only the cooling capacity converts to BTU/h at this fixed ratio. Match like with like before converting.
Why do European ACs use kW while American ones use BTU?
Pure convention, not physics. Both the kilowatt and the BTU/h measure thermal power. Europe and Asia adopted the SI kilowatt when they standardized; North America kept the British thermal unit that its HVAC trade had used since the 19th century. The conversion between them is an exact constant — 0.0002930710702 kW per BTU/h — so a machine rated in one can always be re-read in the other.
More: btu/h to watts · btu/h to ton · btu to kwh · Energy Hub