The size of your radiator shapes how a room feels – the warmth, the comfort, the efficiency. Get it right, and you’ll enjoy a space that feels good to be in, without wasting energy or overheating. But how do you know what size you need?
Our 5–step guide has all the essential information – how to calculate the right heat output for your room, understand BTUs and watts, and select a radiator that fits your space and your style. And if you still have questions at the end, we’re here to help.
Radiators work best when properly matched to a specific room. A radiator that’s too powerful can overheat the space and waste energy. And if it’s too small, it won’t provide enough warmth. The right size will keep your room comfortable and help your heating system work efficiently
N.B. If you’re heating a large space, consider using multiple radiators to spread heat evenly. This prevents cold spots and gives you greater control over the temperature across the room.
You might see the output of a radiator expressed in two ways – BTUs or watts. Watts are an international standard that shows the power output of the radiator.
BTU stands for British Thermal Unit and is a similar measurement – a measure of thermal energy that lets you know how much heat a radiator can deliver per hour. Higher BTU ratings mean more heat. Once you know your room’s required BTU or watts, you can look for radiators that match or exceed that number.
To convert between watts and BTUs
1 watt = 3.41 BTU/hour
1 BTU = 0.293 watts
You’ll find both BTUs and watts listed on every radiator we stock.
There is an important consideration when choosing your radiators as it is the basis upon which radiators should be compared. For a radiator to be giving you the heat output specified it needs to be properly tested and certified to European Standard BS-EN442. It is the law that products installed on a building’s heating system conform to this industry standard and, as a result, will be given a ‘UKCA’/ ‘CE’ mark.
The test is a simple one that calculates outputs based on set criteria and ensures all radiators are measured equally. The results, according to EN442 standards, are referred to as Delta (or using this symbol Δ) t50 and is there to guarantee plumbers, and consumers alike can accurately compare the heat outputs of different radiators against each other.
Disappointingly, some radiators show outputs based on higher Delta t results (Delta t60 or even 75) which assumes abnormally high operating temperatures of the central heating and, as a consequence, may result in the radiators not preforming as expected when included on a heating system operating at its most energy efficient.
This may well result in radiators not being suitable for the rooms they are planned for, leaving you cold and out of pocket, as you will need to turn the heating up to get the desired room temperature.
Every room needs a certain amount of heat to feel comfortable. How much depends on variables such as its size, how it’s used, type of glazing and insulation. The best place to start is with the number of watts/BTUs required for the space – and it’s easy to find yours with our BTU calculator.
Simply enter a few room details and get a result in BTUs and watts – two key numbers that will guide your radiator choice. Once you have them, you can compare radiators based on their heat output and choose one that fits your space and your style.
We’ve seen the importance of radiator size, but there are several other important factors to think about too:
These details all affect your BTU result – and our heat calculator can take them into account.
Once you know your room’s required heat output, you can explore radiators that deliver your specification. If you’ve fallen for a design with a slightly higher output, you can easily regulate the heat using thermostatic radiator valves. If you’re stuck between options, we’re here to help you make the best choice for your room.
Visit a showroom to explore in person, or get in touch to chat with our team.
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