Air Conditioner Size Calculator

How to calculate the size of air conditioner you need

It is important to select the correct size of air conditioner for a room. Too small and the air conditioner will be working too hard, the room will not be cool enough and you may get condensation problems. Too large and your air conditioner may be constantly switching on and off.

This is a simple calculator to help you decide what size of air conditioner you will need. This is based on the most commonly used air conditioners these days which are split units with a CoP of 4. CoP stands for Coefficient of Performance - how efficient the air conditioner is and modern air conditioners can move 4 kilowatts of heat by using only 1 kilowatt of electricity.

Standard air conditioner sizes available for domestic use:

The range of sizes varies between companies. Having said that they do tend to fall into specific preferred sizes. Generally speaking standard air conditioner sizes available for domestic use are:

NOTE: These are the sizes quoted by manufacturers. When they quote sizes in HP or watts this refers to the input power the air conditioner uses, when sizes are quoted in BTUs this refers to the output ie. the amount of cooling achieved which is usually nearly 4 times the input power.

Size measurement in watts, BTUs horsepower and PK:

Different brands of air conditioners use different ways of indicating their size, for this reason 3 different size equivalents are given above:

1. HP or horsepower. Note that PK (pronounced peka) is Dutch for Horse Power which is the common sizing of air conditioners in Indonesia.

2. BTUs (British Thermal Units) the common sizing used in America.

3. The electrical power rating in watts (this is watts of input power not output watts).

Input power versus output power

It is important to note that the HP, PK and watts figures indicate the amount of power input, the BTU figures indicate the amount of cooling output achieved. The actual cooling achieved in BTUs depends on the efficiency of the air conditioner. The above figures are given as an approximate guide of what you might expect with normal modern air conditioners.

How insulated is your room? It makes a difference

Insulation makes a huge difference. The better a room is insulated the less air conditioning you will need. As a rough guide:

Well insulated room

A might have thick solid walls, an insulated ceiling, close fitting doors and few or double glazed windows and not many people in it.

Medium insulated room

A medium insulated room might have solid concrete walls, close fitting doors, an insulated roof and few standard windows.

Poorly Insulated Room

A poorly insulated room might have large window area, poorly fitting doors, a roof or walls that give off heat internally or a lot of people in it.

See also:

• Buying an air conditioner
• How an air conditioner works
• Types of air conditioners
• Inverter air conditioners
• Servicing and maintenance of air conditioners
• Air conditioner refrigerants
• Air Conditioner quality and reliability
• Air conditioner water heaters give you fee hot water
• Climate control, temperature, humidity and dew point
• Building insulation