A radiator can look perfect and still leave a room cold if its heat output doesn't match the space. Before you choose a style or finish, it's worth working out roughly how much heat your room needs. Here's a simple guide.
What is BTU?
BTU (British Thermal Units) is the most common way radiator heat output is measured in the UK. You'll also see output shown in watts. The two measure the same thing: 1 watt is about 3.41 BTU per hour. The higher the number, the more heat the radiator gives off.
What affects how much heat a room needs?
- Room size: the length, width and ceiling height of the room. Bigger rooms, and rooms with high ceilings, need more heat.
- Windows: large windows, bay windows and single glazing all lose heat.
- External walls: a room with two or three outside walls needs more heat than one surrounded by other rooms.
- Insulation: older, solid-walled properties usually need more output than modern, well-insulated homes.
- How you use the room: living rooms and bathrooms are usually kept warmer than bedrooms or hallways.
ΔT50 and ΔT60: why two figures?
On our product pages you'll often see two heat outputs, labelled ΔT50 and ΔT60. These describe the difference between the water temperature in the radiator and the temperature of the room. ΔT50 is the European standard and is the most realistic figure for most modern UK heating systems. ΔT60 figures are higher, so if you're comparing radiators, make sure you compare like with like, and use ΔT50 when sizing.
If you have a heat pump or a low-temperature boiler setup, the radiator will run cooler, so you'll need a higher-rated radiator (or more radiators) to heat the same room. Your installer can confirm the right figure for your system.
How to use the figure once you have it
- Choose a radiator at or slightly above the output you need. A thermostatic radiator valve (TRV) will stop it overheating, so a little extra is better than too little.
- Split it across two radiators in large or open-plan rooms, for more even heat.
- Check the size fits your wall space and, if replacing an old radiator, the existing pipe positions.
Need help?
Working out heat output can be tricky, especially for unusual rooms or older properties. Our team is happy to help you choose the right size: call us on 01206 913565 (Monday to Friday, 9:00am to 5:30pm) or email sales@traderadradiators.co.uk with your room measurements.