Room and Air Conditioner Sizing Guide

We’ve put together an easy to follow guide to help you choose the air conditioner that best suits your needs. You’ll find out what BTUs are and what number of BTUs your air conditioner requires to cool your space.

What is BTU?

BTU is a unit of measurement used to determine the heating or the cooling capacity of an appliance in the UK and the USA, designating British Thermal Units. 1 BTU is the amount of heat needed to raise the temperature of one pound of liquid water by 1 degree from 60° to 61° Fahrenheit, while maintaining a constant pressure of 1 atmosphere.

Another common measurement is kWh (kilo Watt hours) - and the power of all our air conditioners is given in both kWh and BTUs.

As a rule of thumb, an air conditioner needs approx. 25 BTUs for each square foot of space - in ideal and standard room conditions.

What affects the number of BTUs?

  • Room size
  • Window size
  • Direction in which the window faces
  • Number of people/devices in the room

The light received into a room is a significant factor in the temperature the room maintains. For example, South-facing conservatories can get very warm, even in spring or autumn, and will require a more powerful air conditioner that their area or volume would suggest.

In general, we advise purchasing an air conditioner with a minimum output of 8,000 BTUs as this is the minimum BTUs required to cool a small room (18 m2) on a hot day. Medium rooms (24 m2) need around 10,000 BTUs, while larger rooms and office spaces (36-46 m2) require at least 12,000 BTUs.

Two or more air conditioners may be needed if your requirements exceed 15,000 BTUs.

Room Type Room Size Room Area BTUs
Small Bedroom or Office

15 ft. x 20 ft.

4.5 m x 6 m

Up to 350 sq. ft.

Up to 32 m2

10,000

 

Bedroom

20 ft. x 20 ft.

6 m x 6 m

Up to 450 sq. ft.

Up to 42 m2

12,000
Large Bedroom or Living Room

20 ft. x 22 ft.

6 m x 7 m

Up to 500 sq. ft.

Up to 46 m2

13,000
Large Living Room or Great Room

20 ft. x 25 ft.

6 m x 8 m

Up to 550 sq. ft.

Up to 51 m2

14,000


For ease, we have organised our air conditioners in to the following categories of room size and application:

Small & Medium Rooms Medium & Large Rooms Offices & Small Commercials
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