A Quick Guide to Replacing a Radiator Like-for-Like

A man hanging a radiator on the wall
16 November 2023 780 view(s) 3 min read
A Quick Guide to Replacing a Radiator Like-for-Like

If you want to replace a radiator without having to change the existing pipework, it needs to be the 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. 

We recommend you measure in millimetres(mm), 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 measure 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.


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 that 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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