Get the right level of toasty for your room

BTU stands for British Thermal Units and is a measure of how much heat a radiator can output to increase the temperature of a room. While it might seem like a higher BTU is always better, the most efficient choice is a radiator that’s correctly matched to the size and characteristics of your space.

Read me: Why you need a BTU calculator to calculate a room's heating requirement 

Radiator heat outputs are usually measured using a standard called Delta-T 50°C (ΔT50), which compares the average water temperature inside the radiator with the room temperature.

Modern heating systems often run at lower temperatures (around ΔT30) to improve efficiency and support technologies such as heat pumps. Because radiators produce less heat at lower temperatures, manufacturers may now show both figures.

As a rough guide: BTU (ΔT50) × 0.51 ≈ BTU (ΔT30)

If you’d like to dig a little deeper into how radiator heat output is measured, our guide to Delta ratings explained breaks it down.

If your calculated BTU requirement is particularly high and radiator options seem limited, it may be a sign that adding a second radiator could be the best way to heat the space effectively.

For example, a new extension that spans the width of your home might ideally need two or even three radiators to make it nice and toasty. Also factor in underfloor heating - you might want to heat a space with a combination of these two heat sources. If you're not sure how to achieve the best product mix, we can absolutely help - call, email or pop onto live chat and we can help guide you to the perfect solution. 

Sounds like a fabulous space to heat! At the moment our calculator is still learning but we hope to add this option of selecting multiple radiators soon.

In the meantime, simply take the total BTU requirement and divide it by the number of radiators you’d like to install. You can filter by BTU on our category pages and every product page has a clear BTU figure displayed so this should make it easy for you to choose the most efficient combination for your home.

Stuck on product selection? Call, email or pop onto live chat and we can walk you through some options!