How To Work Out What Size Air Conditioner Is Right For Me?

January 26, 2023

When we talk about the size of an air conditioning system, we’re not talking about the dimensions of the unit, but its capacity to heat or cool a room. The capacity is measured in Kilowatts (kW). If you are interested in installing air conditioning, our guide will help you work out what size air conditioner is right for you.

How Many Kilowatts Do I Need?

A simple calculation will help you to work out approximately what size air conditioner is right (unless you’re using our guide below). First, calculate the floor area of the space to be cooled or heated by multiplying the length of the space by the width. For example, a room with a length of 8m and a width of 6m will have a floor area of 48 sq. metres.

Next, you will need your ceiling height, and this will determine the number of watts to be used in the calculation. 

2.4m height = 150 watts

2.7m height = 160 watts

3.0m height = 175 watts

If your ceiling was 2.7m in height, then this would be the calculation: 

48 sq. metres x 160 watts = 7,680 watts or 7.68 kW.

Square Metres & Kilowatts

The output of your air conditioning system should suit the size of your room(s). Even the most expensive unit designed for a 10m² room won’t cool a 50 m² facility. Below is a table to help you work out what size air conditioner is right for you, but speak to a professional air conditioning engineer about the correct size for your needs. 

Floor Size (m2)System Size (2.4m Ceiling Height)System Size (2.7 Ceiling Height)System Size (3.0m Ceiling Height)
10-152.0kW – 2.2kW2.0kW – 2.4kW2.0kW – 2.6kW
15-202.2kW – 3.0kW2.4kW – 3.2kW2.6kW – 3.5kW
20-253.0kW – 3.7kW3.2kW – 4.0kW3.5kW – 4.3kW
25-303.7kW – 4.5kW4.0kW – 4.8kW4.3kW – 5.2kW
30-354.5kW – 5.2kW4.8kW – 5.6kW5.2kW – 6.1kW
35-405.2kW – 6.0kW5.6kW – 6.4kW6.1kW – 7.0kW
40-456.0kW – 6.7kW6.4kW – 7.2kW 7.0kW – 7.8kW
45-506.7kW – 7.5kW7.2kW – 8.0kW7.8kW – 8.7kW
50-557.5kW – 8.2kW8.0kW – 8.8kW8.7kW – 9.2kW
55-608.2kW – 9.0kW8.8kW – 9.2kW9.2kW – 10.5kW

Take Room Traits Into Account

When working out what size air conditioner is right, the above table provides a general rule of thumb, but there are other factors to consider. 

If you’re wanting to heat or cool one central room, then the calculations above will be a useful guide. However, if you want to heat multiple rooms, then getting units for each room might be right for you. 

Depending on whether the room you’re looking to cover is shaded or in the sunlight, you may have to adjust the number power of your unit. You’ll need 10 per cent less capacity for shaded rooms, and 10 per cent more capacity for rooms in the sunlight. 

If your air conditioning system is for a kitchen or a room with other appliances that generate heat (such as an IT room), you will also need to increase the capacity of your unit. 

Other traits to take into account are whether the room has windows and how much insulation the room has. Poorly insulated homes or buildings may also need a higher output to cool properly. Rooms where much of the wall is glass will heat up more than those that don’t, especially if the windows are south facing. Rooms on higher floors will also need more cooling capacity as heat rises. 

The type of space may impact your calculation. Open-plan areas are the easiest to evaluate, whereas it may be more efficient to cool smaller offices individually. Hallways, corridors, and reception areas may not be occupied so you may wish to not cool these areas. 

The location of the units will also need to be a consideration. Indoor units will need to be placed higher to allow cooler air to flow downwards. If this isn’t possible, a more powerful system will be needed to ensure the system runs efficiently. For the outdoor unit, a north or south-facing wall will be best to avoid the unit heating up and having to work harder throughout the day. 

Do’s & Don’ts

Do: Install A Wall Mounted Or Central Air Conditioning System

Installing a wall-mounted or central system rather than a window or portable air conditioning system could be more efficient and cool your room better. Window or portable systems are more likely to sit lower in the room. Wall-mounted or central systems are more likely to sit higher with cold air filtering down and cooling the temperature more efficiently. 

Don’t: Get A System Too Small For The Space

A smaller air conditioning system won’t cool (or heat) the space efficiently. They will need to run for longer periods of time and even then they may not effectively cool the space. It will definitely increase your electricity bill. 

Don’t: Get A System That Is Too Large For Your Space

It’s OK to err on the side of a slightly larger system for your room to ensure adequate comfort, but getting a system that is much too big for your space can also cause problems. 

A larger system will cool the air in the room much more quickly and begin to cycle on and off. If it is constantly on and off, it may not run long enough to extract the humidity from the room, leaving users feeling uncomfortable. 

Systems that are too large or small for the space also run inefficiently leading to increased workload and ultimately, increased electricity costs. 

Speak To A Professional

As ever, this is a simple guide to evaluate your needs when looking to install a new or replace an old air conditioning system. Speak to a professional engineer who can advise what size air conditioner is right for you.