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Your Guide to Replacing a Radiator Like for Like

Updated: Jun 17

A plumber fitting a new white radiator to the wall whilst a woman watches him

If you want to replace a radiator without having to change the existing pipework, it needs to be the exact same size – in width and depth – and ideally, your valves must have the same connecting tails. Here’s a quick guide to measuring up, to help avoid any mistakes. We also look at the importance of getting the BTUs right too.

We recommend you measure in millimetres, as this is the standard unit of measurement for radiators.

  1. Measure from the lowest to the highest point to get the radiator’s height.

  2. Then measure from one side to the other, for the width.

  3. It’s also important to take a measurement from the centre of the left-hand pipe to the centre of the right-hand pipe. If you are looking to use new valves check whether the connecting tails are longer or shorter – if they are, you will need to change the width of the radiator accordingly – or use a suitable valve tail extension to bridge any gap.

  4. To ensure you choose a radiator that sits the same distance from the wall, measure the distance between the wall and pipe centres, from the centre of the pipe (on either side) to the wall. This is to ensure the pipes easily connect, as different bracket and/or radiator designs will have an effect.

  5. Also, take the ‘wall to face’ measurement - from the wall to the front of your radiator. If you are short on space, you may be able to source a more slimline radiator.

A picture displaying a white radiator with markings indicating what the width of the radiator is and what the pipe centres are.

Measuring the Heat Output

You also need to make sure that any radiator you choose will output enough heat to warm up your room. Although one radiator may have the same dimensions as another, other factors such as material and design can affect the heat output. This can mean that despite two radiators being the same size, they may have different levels of heat output. To do this, calculate your room’s heating requirement in BTUs (British Thermal Units), using our Heat Output Calculator. Then check that your chosen radiator can give you the required BTU.

Please note: BTU calculators will always show you the combined heat output of all radiators/towel rails required for your room. Larger rooms such as living rooms may have or require more than one radiator positioned evenly throughout the room. If this is the case, divide the required output between the number of radiators needed

Now you’ve got everything you need, you’re ready to choose your new radiator – but do note, some minor pipework alterations or adjustments may still be needed, but a good plumber can usually find a solution that minimises any disruption.

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British Thermal Units (BTU) is a measure of the output of heat needed to raise the temperature of a room. Determining the correct BTU will help you get the right radiator for your home.

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