BTU Calculator
Find the right radiator size for any room
Use our easy-to-use BTU calculator to work out the heat output you need for your space. Get an estimate in seconds and browse our range of radiators to match.
and easy to use
BTU requirement
the right radiator
Room details
Enter the size of your room
Room type
Tell us what kind of space it is
Exposure
How exposed is the room?
Windows
Select your window type
Your estimated heating requirement
Enter your room details and calculate to see your estimated heating requirement.
View suitable radiators →Suggested radiator size
For this room, we recommend looking for a radiator with a heat output of approximately:
This is an approximate guide. Insulation, window area and heating-system temperatures can affect the output required.
How to choose
the right radiator size
Learn more about BTU, heat output and everything you need to consider when choosing a radiator.
Frequently asked questions
What does BTU stand for?
BTU stands for British Thermal Unit. Radiator heat output is commonly expressed in BTU per hour, helping you compare how much heat different radiators can provide.
What does Delta-T 50°C mean?
Delta-T 50°C describes a standard temperature difference used to rate radiator output. If your heating system operates at lower water temperatures, the radiator may produce less heat than its published Delta-T 50°C rating.
What if my BTU figure is very high?
A large or exposed room may need a higher-output radiator or more than one radiator. Consider obtaining a detailed heat-loss calculation before purchasing.
Should I choose a larger radiator than the calculated BTU?
A modest allowance can sometimes be useful, but the appropriate size depends on your heating system, insulation and design temperatures. A professional heat-loss calculation provides greater accuracy.
Does room insulation affect the BTU requirement?
Yes. Poorly insulated rooms generally lose more heat, so they require greater heating output than similarly sized well-insulated rooms.
