How many BTU do I need? Table by room size

Table: area → capacity

Valid for ceilings up to 2.7 m, normal insulation and up to two windows without direct southern sun all day.

• 7000 BTU (≈2.0 kW) – 10–16 m²: small bedroom, study
• 9000 BTU (≈2.6 kW) – 15–25 m²: bedroom, nursery
• 12000 BTU (≈3.5 kW) – 25–35 m²: large bedroom, small living room
• 14000 BTU (≈4.1 kW) – 30–40 m²: living room
• 18000 BTU (≈5.3 kW) – 40–55 m²: living room with kitchen, office
• 21000 BTU (≈6.2 kW) – 50–65 m²: large living room, shop
• 24000 BTU (≈7.0 kW) – 60–75 m²: open-plan space, venue

When to size up

Each factor below adds roughly 10–20% to the required capacity. With two or more, move to the next step in the table.

• South- or west-facing with large windows
• Top floor under an uninsulated roof, or an attic
• Ceiling above 2.7 m
• Kitchen in the same room, or many appliances (an office full of computers)
• More than 3–4 people in the room most of the time
• The unit will be the main winter heating

Why not simply the most powerful one

An oversized unit reaches the set temperature fast and switches off before it has dehumidified the air – the room feels cold and clammy. It also costs more and has a larger outdoor unit. An inverter compensates for a small margin, not for double the capacity.

BTU and kilowatts

1 kW ≈ 3412 BTU/h. Manufacturers quote both; heat pumps and some professional systems are rated in kW only. For heating, the figure that matters is the heating output at low outdoor temperature, not the nominal one.