If you're replacing a radiator or choosing one for a new room, the space beneath a window is often the obvious place to install it. But how do you know what size radiator you need?
Choosing the right radiator isn't simply about finding one that fits the available wall space. You also need to consider the size of the room, the amount of heat required and the radiator's heat output.
In this guide, we'll explain how to choose the right radiator for the space beneath your window, including how to measure the available area and why BTU output matters.
Why Are Radiators Often Installed Under Windows?
Radiators are traditionally positioned beneath windows because this can help counteract cold air entering the room through the window area.
As the radiator warms the air, it rises and circulates around the room, helping to create a more even temperature.
Modern windows are generally much more energy efficient than older single-glazed windows, so installing a radiator beneath a window isn't always essential. However, it can still be a practical location, particularly where wall space elsewhere is limited.
For many homes, the bigger consideration is simply making the most of the available space without compromising heating performance.
How Do I Measure for a Radiator Under a Window?
Before choosing a radiator, measure the available wall space carefully.
You'll want to know:
The width of the available space
The height available beneath the window
The distance between the floor and the bottom of the window
The position of your existing pipework
The location of skirting boards, sockets and other obstructions
It's important not to choose a radiator that is simply the maximum possible size. You'll need to allow enough space around the radiator for installation, pipework and airflow.
If you're replacing an existing radiator, measuring the current radiator can also be a useful starting point. However, don't assume that the replacement needs to be exactly the same size. The new radiator's heat output is just as important as its physical dimensions.
What Size Radiator Do I Need?
There isn't one standard radiator size for a particular window.
The correct radiator depends primarily on the heat requirement of the room, rather than the size of the window itself.
This is where BTUs come in.
What Does BTU Mean?
BTU stands for British Thermal Unit and is commonly used to describe the heat output required from a radiator.
A radiator with a higher BTU output will produce more heat than one with a lower BTU output.
To choose the right radiator, you should calculate approximately how many BTUs your room requires and then select a radiator, or combination of radiators, capable of providing that output.
Room size, ceiling height, insulation, window type and the number of external walls can all affect the amount of heat required.
Does the Radiator Need to Be the Same Width as the Window?
No. Ideally, you want to make the most of the available wall space, but the radiator doesn't necessarily need to match the width of the window.
For example, you might have a relatively wide window but only need a smaller radiator based on the room's heat requirement. Equally, a larger room may require a radiator with a greater heat output than a single compact radiator beneath the window can provide.
If space is limited, vertical radiators can be a useful alternative. They provide substantial heat output while taking up less horizontal wall space.
This can be particularly useful in rooms where the area beneath the window is narrow or already occupied by furniture.
What If My Window Is Very Wide?
A wide window doesn't necessarily mean you need one very wide radiator.
Depending on the room's heat requirement and available wall space, you could consider:
One large horizontal radiator
Two smaller radiators
A vertical radiator elsewhere in the room
A combination of different radiators
The best option will depend on the room layout and required heat output.
It's also worth considering how the radiator will look within the space. A radiator should provide sufficient heat, but it doesn't have to dominate the room.
How Much Space Should You Leave Around a Radiator?
Radiators need adequate clearance to allow air to circulate effectively.
Avoid positioning furniture directly against or over a radiator, as this can restrict airflow and reduce its effectiveness.
You'll also need to consider the distance between the radiator and:
The floor
The window sill
Skirting boards
Furniture
Curtains
The exact installation requirements can vary between radiator designs, so always check the manufacturer's installation instructions for the model you've chosen.
What If I Don't Have Enough Space Under the Window?
Don't worry if the space beneath your window isn't large enough for the radiator you need.
There are plenty of alternatives.
Choose a Vertical Radiator
Vertical radiators make use of wall height rather than width, making them particularly useful where horizontal wall space is limited.
They're available in a wide range of styles and finishes, so they can also become a feature within the room rather than simply blending into the background.
Consider More Than One Radiator
For larger rooms, using two radiators can sometimes provide a more practical solution than trying to fit one oversized radiator into a single location.
Distributing heat around the room can also work well from a layout and interior design perspective.
Consider a Different Wall
The radiator doesn't necessarily have to sit beneath the window.
If another wall provides a better position for the size and style of radiator you need, it may be worth considering an alternative layout.
Should I Choose a Double or Single Radiator?
Radiators with different numbers of panels and convector fins can provide significantly different heat outputs even when their external dimensions are similar.
This means you shouldn't select a radiator based solely on its width and height.
If you're working with limited wall space beneath a window, choosing a radiator with a higher heat output for its physical size can help you achieve the heat requirement without needing a much larger radiator.
Don't Forget the BTU
One of the most common mistakes when replacing a radiator is choosing a model based purely on appearance or dimensions.
A radiator might fit perfectly beneath your window but still be unsuitable if its heat output is too low for the room.
Before ordering, establish the approximate BTU requirement and compare this with the radiator's stated heat output.
If you're unsure about the heat output you need, the team at House of Heating can help. We can help you determine the right radiator output for your room and heating system, so you can choose a radiator that provides the warmth you need.
Finding the Right Radiator for Your Space
The ideal radiator should strike a balance between size, heat output, position and style.
If you're installing a radiator beneath a window, start by measuring the available space. Then work out the heat requirement for the room before choosing a radiator that provides the necessary output while fitting comfortably into the available area.
And remember, the radiator that looks right isn't necessarily the radiator that's right for the room.
At House of Heating, we offer a wide range of radiator styles and heating solutions, helping you find a radiator that works as hard as it looks good.
Looking for your next radiator? Explore our range of heating solutions and find the right option for your space.
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