Calculating the size of an air conditioner

The amount of heat generated in a room is known as the heat gain or load of that room. Heat is measured in either British Thermal Units (BTU) or Kilowatts (kW). 1 kW is equivalent to 3412 BTUs.

The heat load of a room depends on a number of factors including the area of the room, position and number of windows, sunlight, equipment and lighting.

A starting point to calculate the cooling requirement of a room is to multiply the length and breadth of a room (in metres) and multiply by 500. i.e.

Room BTU requirement = Room length (m) X Room breadth (m) X 500

Air conditioning units generally start at 9000 BTU size and increasing in roughly 3000 BTU increments. A slightly more powerful unit than required is generally recommened to account for additional heat loads and to ensure that the air conditioner is not overloaded.