A British Thermal Unit (BTU) is a measure of heat output from a radiator. Depending on the size of your room, the number and type of windows and what the room is used for, you'll need more or less heat. If you have a higher BTU requirement, it might be better to use more than one radiator to deliver the heat you'll need to a room. The total BTU output of several smaller radiators may meet your needs.


If you are entering your room measurments using feet then enter the measurments with a comma. For example 12 feet 3 inches would be entered as 12,3. Exactly 12 feet would be simply 12.


  Length Width Height


Ft,In Ft,In Ft,In


Room Type?


Does the room have?

  French Windows  
    North Facing Walls  
    Double Glazing  
  Required BTU Watts

This calculator will give an approximate value of the BTU requirement for your room. Consider other factors such as if the room has large windows or more than one outside walls.

Please call us on 01663 749027 for advice.


Delta T 50 ° Converter

If you have been looking at radiators for any length of time you may have noticed the term ‘Delta T’. Delta T is a rating of the heating system.

It is calculated by the following method. Take an average of the following:

Temperature of the water going into the radiator °C

Temperature of the water coming out of the radiator °C

Then deduct the room temperature of 20°C

The European Union standard is Delta T 50. Radiator manufactures in the UK should be using this standard. Some suppliers are not using this standard as a way of inflating the heat outputs of their radiators.

To use this converter simply enter the BTU value for the radiator and select the Delta T value in the drop down.

For example, if you have a brochure showing a radiator rated at 3996 BTU Delta T 70, then enter 3996 in the BTU field and change the selector to 70. In Delta T 50 that should give 2850.

BTU Watts Delta T
BTU or Watts
The value in Delta T 50 ° is BTU which is Watts

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