Heat Output Calculator 
How to Choose the Right Radiator and/or Towel Rail

BTUs stands for 'British Thermal Units' and is a measurement of thermal energy. It is always worth remembering that there are several factors involved when it comes to calculating the output you require from your radiators in order to heat your room efficiently. 

Use our Heat Output Calculator below to find your required heat output. Enter the required information and our calculator will provide a guide as to how many BTUs you will need in order to make sure your room is warm and cosy. 

Once you've got your calculation you'll be able to shop with confidence:

How to Calculate Heat Output to BTUs for Your Room

Ultimately, employing the services of a plumber will yield the most accurate results. That being said, our calculator below will provide you with a good guide as to what BTUs will be required to ensure your room is heated properly, which also serves to optimise your heating efficiency.


Please note: this is a guide only and will show you the combined heat output of all radiators/towel rails required for your room. Larger rooms such as Living Rooms may require more than one radiator positioned evenly throughout the room. If this is the case, divide the required output between the number of radiators needed.


  • A radiator with insufficient output may never raise the temperature of the room to that which is required. 

  • Outdoor temperatures, external walls, insulation, heated adjacent rooms (i.e. above, below and to the side) will all play a part.


  • The boiler should be sufficient enough to supply all connected radiators to the sum of their maximum demand.

Calculate Your Room's BTU Requirement

Step 1 Enter Room information
Step 2 Enter Room Dimensions

Please select whether like to provide the room dimensions in meters or feet

Require BTU's

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Your Calculation Result

This result is shown as a range to compensate for unknown factors such as external temperatures and levels of insulation in your home. We recommend the combined heat output of all the radiators in your room meets the higher end of this result to ensure your room is heated efficiently.

Required BTUs
Require BTUs
(Δt 50°C)
Required Watts
(Δt 50°C)
Require Watts
You've Calculated Your BTU Requirement, What Now?

Now that you've worked out your heat output requirements, make a note and keep them to hand. From here you can view our range of radiators and/or heated towel rails whilst referencing the output displayed on each against your calculations, this way you can ensure that you're choosing the perfect radiator/towel rail for you.

Remember that our calculator will show you the combined output required for the provided room measurements; in the case of larger rooms that require more than 1 radiator, divide the calculated output by how many you need.

White Column Radiator
White Heated Towel Rail on a bathroom wall
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