Not sure what size radiator you need? This simple guide explains how to choose the right radiator based on your pipe centres, room size, and heat output requirements.
Step 1 — Measure Pipe Centres (For Replacement Radiators)
If you are replacing an existing radiator:
- Measure the distance between the centre of your pipes
- This measurement determines the radiator width you need
Most radiators have pipe centres approximately 45mm less than the total width. For example, a 400mm wide radiator typically has a 355mm pipe centre.
Important: Always check the product description, as some models may vary.
Step 2 — Choose the Right Radiator Size
Radiator size depends on:
- Wall space available
- Room size
- Heat output required
Taller radiators provide more heat output, while wider radiators cover more wall space. Vertical radiators are ideal for compact rooms where wall width is limited.
Step 3 — Understand Heat Output (BTU)
BTU (British Thermal Unit) measures how much heat a radiator produces.
As a general guide:
- Small bathroom: 1,000–2,000 BTU
- Bedroom: 2,000–4,000 BTU
- Living room: 4,000–8,000+ BTU
Larger or poorly insulated rooms will require higher BTU radiators.
Why Choosing the Right Size Matters
Selecting the wrong radiator size can lead to:
- Rooms not heating properly
- Increased energy bills
- Extra strain on your boiler
- Having to return an unsuitable towel rail or radiator
Tips for Choosing the Right Radiator
- Always check the BTU rating before buying
- Choose a slightly higher output for colder rooms
- Consider vertical radiators for small spaces
- Ensure pipe centres match your existing setup
Need Help?
If you're unsure what size radiator you need, our team is happy to help. Contact us via live chat, email, or phone for expert advice.