How much cooling capacity does a whole house need?

Around 10 kW of total cooling (34,000 BTU) with average insulation — typically delivered as a trial or quad split: for example 12,000 BTU in the living room and 9,000 BTU in two or three bedrooms. Well-insulated homes drop to ~8.5 kW, old ones with big west-facing windows climb toward 11.5 kW. You rarely run all units at once, which multi-split systems exploit.

Internal heat gains: each person emits roughly 100-120 W (about 400 BTU/h), each workstation with monitor another 100-200 W, plus lighting, printers and often more glass. Ten people with ten PCs in 80 m² add as much heat as the sun through a large window. That’s why the calculator uses ~450 BTU/m² for offices versus 340 for homes — and why meeting rooms need their own generous unit.

Multi-split, almost always. Cold air doesn’t travel through doorways well, so a single 24,000 BTU unit in the living room leaves bedrooms warm while freezing the sofa. Separate indoor units give per-room temperatures, quieter operation (each unit runs low), and better efficiency since you only cool occupied rooms. The single big unit only wins in genuine open-plan spaces.

Less than people fear with modern inverters: 10 kW of cooling at SEER 7 draws about 1.4 kW at full tilt, and far less once rooms reach temperature — a realistic summer average is 0.5-0.8 kWh per hour of use for a whole apartment. At €0.25/kWh, an 8-hour day costs €1-2. The real bill-killers are poor insulation, doors left open, and setting 20 °C instead of a sensible 26-27 °C.