Measure the length and width of the room in metres, then multiply them to get the area in square metres. For open-plan or irregular rooms, measure each section separately and add the areas together.

Most standard bedrooms suit a 2.5kW split system, but room size, insulation, sun exposure and ceiling height can change the required capacity.

Stick with established brands that support their warranty and parts network. Cheap systems can cost more over time if warranty support, parts or service access is poor.

Many major brands offer five-year warranties, but warranty support is only useful when the brand has strong local backing and responsive service support.

For ducted systems, size depends on the rooms you want to use at the same time, plus insulation, ceiling height, glazing, orientation and heat load. A site assessment gives the most accurate result.