Home & DIY
How much cooling capacity does a whole house need?
Total cooling capacity and number of indoor units for a whole home, office or shop, based on area and insulation.
Quick answer
Cooling a whole home or office is not "one big room" math — it’s a budget of heat sources. A home needs roughly 340 BTU per square metre; an office needs about 450, because every person adds ~400 BTU/h and every computer another 300-600; a shop with glass frontage and constant door traffic pushes 500. Insulation and sun exposure swing the total by ±15%, which on 100 m² is the difference of an entire split unit.
Total cooling capacity
34,000 BTU/h
- In kilowatts
- 10 kW
- Indoor units (multi-split)
- ~3 × 9,000-12,000 BTU
- Electrical draw (approx.)
- ~1.4 kW
Rules of thumb: ~340 BTU/m² for homes, ~450 for offices (people and computers add heat), ~500 for shops, corrected for insulation. Only cool the rooms you actually use — a multi-split with one indoor unit per main room beats one giant unit pushing air down a hallway. Electrical draw assumes a modern inverter with SEER around 7: cooling power ÷ 7. For spaces over 200 m² or open-plan offices, get a professional load calculation.
How it works
The second decision is how to distribute that capacity, and here the rule is simple: cool rooms, not corridors. A multi-split system — one outdoor unit feeding an indoor unit in each main room — beats a single oversized unit trying to push cold air through doorways, both for comfort and for electricity. The calculator suggests how many 9,000-12,000 BTU indoor units your total implies, plus the approximate electrical draw with a modern inverter (SEER ~7): useful to check your meter capacity before an installer does. Above 200 m², or for open-plan offices with server rooms, a professional load calculation stops being optional.
Sizing the cooling correctly and then not being able to switch it on is a common way to discover the second constraint: the contracted electrical supply. A multi-split running with the oven and an induction hob is enough to trip a standard 3 kW household supply, and raising it to 4.5 or 6 kW is a permanent increase in the fixed part of the bill, not a one-off fee. Work out the worst realistic simultaneous load before you commit to the system, because the upgrade is cheap to request and annoying to discover in August.
Frequently asked questions
How many kW of air conditioning for a 100 m² house?+
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.
Why does an office need more cooling than a home?+
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.
One big unit or a multi-split with several small ones?+
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.
How much electricity does whole-house AC use?+
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.
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