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What is a BTU?

What we’ll cover…

  • What a BTU is
  • Why BTUs play an important role in choosing the right radiators
  • How to work out BTU needs for individual rooms
  • Ways to match a radiator BTU output to specific room requirements
  • Tips to use an online BTU calculator tool
  • The advantages of purchasing properly sized radiators in line with BTU requirements

Exploring British Thermal Units

If you’ve been browsing our collection of radiators and heated towel rails, there is no doubt that you’ve come across the letters BTU.

But what does BTU stand for and what does it mean?


The BTU rate of a radiator is a quick and easy way of letting you know how much heat a radiator will emit, and is basically there to help you decide if a radiator is the correct size for your room or not.

It’s important to know just how much heat each room of your home needs in order for your system to work efficiently and for you to have a space that is neither too hot or too cold.

Design, style and finish are all very important factors when it comes to purchasing a radiator, but the most important part of making the right decision is the BTU output of the radiator that you need.

Carry on reading to learn all about BTUs.

So what is a BTU?

BTU stands for British Thermal Unit.

A BTU is the measurement used to represent the amount of energy it takes to heat one pound (1lb) of water (about a pint) by one degree Farenheit.

This measurement is more commonplace in the UK, but is also used throughout the world and is most commonly associated with energy, power, air-conditioning and steam generation.

BTU is the standard heat measurement when it comes to choosing radiators, and you’ll see it on the product specifications listed on every radiator and towel rail product page. (Though not on electric radiator listings).

Radiators and BTU

If you are looking to buy a new radiator, taking the time to calculate the correct number of BTUs you’ll need is integral to you making the correct purchase.

Too little BTU output and your room will not reach the required temperature and you’ll suffer from your space being cold and uninviting (and nobody wants that).

Too many BTUs and you could find yourself paying over the odds for heat that you don’t need and being far too warm.

It is important that you select a radiator or heated towel rail that has the adequate heat output for the space it’s been selected to live in.

You wouldn’t put a huge triple column radiator in a pokey little cloakroom, just as much as you wouldn’t put a small, single-panelled convector radiator in a huge open-plan sitting room.

It’s common sense really.

Calculating BTU

Don’t worry, you don’t have to be a mathematical genius to work out the BTU output your radiator needs have – you just need to be handy with a tape measure, count some windows and know what is on the other side of a few walls.

We’ve also got a great guide to calculating BTUs that might help too!

It will show you what you need to do work out your BTU needs in a little more detail and discuss how to use our BTU Calculator.

Our calculator is totally free to use and will make working out the required BTU amount easier than ever before.

You just need to know the area of the room you want to heat and a couple of other details too – like how many windows there are, whether they are single or double glazed and how many radiators there are in the room.

Our app explains in greater detail what it is that you need to enter, and it’s free!

Once you have the required details, you are armed and ready to make the right purchase; one that is better informed and more appropriate to the needs of your home heating.

How to choose the right radiator

  • Measure your room – Know the dimensions of the room you want to heat. Work out the square metre area of the room in order to be accurate with the amount of heat you will need.
  • Count the windows in that space – It is important to factor in the number of windows there are in the space. Draughts will contribute to the final BTU number.
  • Count the radiators you’ll need – Do you need one, two, three or maybe even more radiators to make the most of your central heating.
  • Know what is above and below the room – Knowing what is above and below the room will make a big difference to the final BTU number. Solid floors retain heat very differently to a floor with a cellar or a cavity.
  • Know what is on the other side of each wall in the room – What is on the other side of the wall, and what the wall is made of, will play a big part in the size and output of the radiator you choose.
  • Use our BTU Calculator – Take all of the information you have collected and make sure you have it to hand when you use our BTU Calculator.

Follow the checklist above and you will soon be enjoying the warmth and luxury of efficient, practical and beautiful new radiators that we specialise in here at BestHeating.

Let’s calculate those BTUs!

a hand calculating BTU output on a calculator

We’re sure you’ll find exactly what you’re after.

Stay Safe and Happy Heating.

Frequently Asked Questions

Several factors will determine if cheap designer radiators deliver an adequate BTU output, such as the size of the space they’ll be installed in, as well as the actual radiator size.

Furthermore, what you define as a cheap designer radiator will be influenced by a number of reasons, like what your radiator budget is, and how much you prioritise the look of your designer radiator in relation to performance quality and durability.

Our BTU Calculator can be used to show whether your chosen cheap designer radiator provides a high enough BTU output to adequately heat the room it will be fitted in. And for more information on the subject, you can take a look at our dedicated blog – Cheap Designer Radiators: Too Good To Be True?

British Thermal Units (BTUs) are specifically a unit of energy. Contrastingly, Watts (W) represent a measurement of the rate that energy is transferred.

When a conversion occurs from BTUs to Watts, it is actually essentially a conversion from BTUs per hour (BTU/h) into the equivalent amount of Watts.

One Watt equates to 3.41 BTUs per hour, so you divide the total number by 3.41 to convert from BTUs to Watts.

You can use our BTU Calculator to find the ideal heat output you may need to heat your chosen space.

However, when calculating wattage outputs, it is important to take into account the heat lost through transfer from the heating element, to the heating solution, and then from the heating solution to the metal of the radiator itself.

And while our BTU Calculator will give you a conversion based on some clever mathematics, if you are unsure of what this heat loss calculation may be, and want to be as accurate as possible, it may be advisable to consult a plumber or electrician for advice before purchase.

A single Watt (W) is equivalent to 3.41 British Thermal Units (BTUs) per hour (h).

As such, to convert BTUs per hour into Watts, you have to divide by 3.41.

In order to convert Watts into BTUs per hour, you should multiply by 3.41.

The BTU requirement per radiator will be determined by the amount of radiators featured in a specific room.

So, use a BTU Calculator to work out the total BTU requirement of the space, and divide this total by the number of radiators you are planning to install.

The result will be the average BTU level needed per radiator.

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