Category - Air Conditioning
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Will Scholfield, Engineer

31 Jan : Updated 16 Apr ● 3 min read

What is BTU in air conditioning?


So, you’re looking on the market for a new air conditioner and you’ve come across an unfamiliar acronym - BTU. 

BTU is a measurement of heat and stands for British Thermal Units. When purchasing an air conditioner, it is very important to check the BTU as this tells you how many units of heat the air conditioner can remove. You should ensure that you are purchasing an air conditioner that can remove the correct amount of heat from your home, otherwise you could be wasting your money. This complete guide will help you understand what a BTU is, the BTU needed for your space and factors which affect the BTU.

How to calculate the BTU needed for your home

Although it sounds quite technical - the BTU needed for your home is relatively easy to calculate. 

To work out the BTU needed for the size of your room you need to measure the length and the width of the room (in ft). Multiply the two together and then multiply this by 25. That’s it! 

What can happen if I don’t choose the correct BTU? 

If you choose a BTU that is too low - it will take longer to cool a room and your electricity bill will soar in price. 

Some people believe that if they purchase a higher BTU the room will get cooler faster - this is not correct. If you choose a BTU that is too high - the moisture extraction can not keep up and this can cause a humid atmosphere. This can also put a strain on the system which reduces the lifespan of it as it is having to stop the cooling cycle too frequently. 

Other factors that can affect the BTU

The height of your ceilings 

The calculation mentioned above assumes that your ceilings are the average - 8ft. If you have ceilings that are higher or lower than 8ft this can affect the BTU you need. 

The amount of sunlight 

If the room you are wanting to cool is directly in the sun for a long part of the day, it can affect the amount of power needed. This can mean you need a higher BTU. If the room tends to be in the shade most of the day - you will need a lower BTU. 

Two rooms that are connected 

There may not be a door between two of your rooms or they are connected and you want to cool them both. To calculate the BTU,  simply add the size of the rooms together. 


Is your home well insulated? If the answer is no - it will lose air much quicker meaning a higher BTU is needed. If you have lots of large windows - again go for a higher BTU so that it can keep up with this loss. 

Call our experts. 

When choosing your new air conditioner, BTU is a very important factor to consider. You can attempt to calculate what BTU you need yourself, but it is always better to consult with a professional. 

At BOXT, you can call us on 0800 193 7777 and speak with one of our specialists who’ll help you solve any issues with BTUs. Alternatively, you can always message us on our Live Chat for advice.  

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