BTU Calculator and Radiator Calculator Tools

BTU Calculator and Radiator Calculator Tools

BTU Calculator and Radiator Calculator Tools

Save time, money, and hassle with our radiator calculator and BTU calculator tools. We have created both to make it easy to find exactly the right radiators for your next installation.

BTU Calculator

Use our free BTU calculator to understand the heating requirements of a room. Our simple, five step tool goes through everything you need to calculate heat loss, so you know exactly the BTU needed to warm a room comfortably.

For answers to common questions around BTU calculations, head to our BTU FAQ section.

Radiator Calculator and Selector Tool

Our radiator calculator and selector tool combines everything you need to work out exactly what is required to warm a room. It allows you to use your BTU requirements and the room’s specifications to find exactly the right product from our extensive range of central heating radiators and heated towel rails. This makes it quick and painless to find what you ned to get the job done.

Be sure to register or log-in to your Wolseley online account to see the best trade prices and availability at your local branch.

Radiator selector

For detailed instructions on how to use the radiator selector, read our how to guide or download as a pdf:

How To Use Our Radiator Selector Tool


Select the room, enter the BTU requirement if known, if not known, use the Heat Loss Calculator.

Select your requirements – room type, room size, radiator type, radiator size etc.

View the products and details of your selection.

Simply add the products to your basket, and then proceed to the checkout to order for collection or delivery.

BTU Calculator FAQ

Here we answer some of the commonly asked questions around BTU calculations.

What is a BTU?

BTU stands for British Thermal Unit. The precise definition is that a BTU is the amount of heat energy needed to warm one pound of water by one degree Fahrenheit. This means that BTUs are an imperial measurement.

BTUs are the industry standard measurement of heat output for radiators – the larger the BTU value the more heat a radiator can provide.

How Many BTUs Are In A kW?

The short answer is that 3412 BTU = 1kW.

If you want to be technically correct, BTU is a measure of energy whereas kWs are a measure of power. So, it is more accurate to say that 1kW is equivalent to 3412 BTU/h (BTU per hour).

How Do I Calculate BTU Required To Heat A Room?

To do a thorough calculation of the BTUs needed to heat a room, there are five things to consider:

  1. The type of room.
    Bedrooms, landings, kitchens, and bathrooms are all quite different spaces with different features that affect heating requirements. For example, bathrooms and kitchens are usually tiled with limited wall space, whereas halls are long and thin with plenty of wall space but will typically lose more heat through the front door. By taking these characteristics into account, our BTU calculator ensures the most efficient and most comfortable heating calculation for a space.
  2. The size of the room.
    The bigger a room, the more heat is needed to warm it up. So, you’ll need the dimensions of a room to calculate the required BTU – length, width, and ceiling height.
  3. Windows.
    Rooms lose most of their heat through windows, so in general the higher the surface area of glazing in a room, the more BTUs you will need to keep that room warm. The type of window is also a huge factor – modern double glazing will lose much less heat than single glazed windows with wooden frames.
  4. External Walls.
    Rooms lose heat through external walls - in general the more external walls, the more heat required. Insulation will have a large effect here too, so knowing whether a wall is solid brick, or cavity wall is important.
  5. What is above and below the room.
    As warm air rises, lots of heat is lost through the ceiling. That means if you have heated rooms above and below, you’ll need less heating than if there’s ground below and a pitched roof above.

Our easy-to-use BTU calculator runs through each of these step-by-step to ensure you get the most accurate results.