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BTU Calculator

What is a BTU?

BTU stands for British Thermal Unit. It is a standard measurement to describe heat output. One BTU is the amount of energy it takes to heat one pound of water by one degree Fahrenheit at sea level. A higher BTU value means the radiator has a higher heat output.

To figure out how much heat you need from your radiator, you can use our handy calculator. Factors such as room size, the type of windows, and more can all affect the heat output required to keep your room at a comfortable temperature, so if you have any questions then get in touch with our expert team for advice.

Use our free BTU calculator to easily work out the required heat output of your rooms. When choosing your radiators, the output can be defined in two different ways, ΔDelta T50℃ and ΔDelta T60℃.

Calculate your required BTU & WattsOur BTU calculator provides and upper and lower range based on the selected room.

Please note:This is just a guide for reference only. Larger rooms, such as living rooms may require more than one radiator positioned throughout the room. If this applies to you, divide the required output between the number of radiators required.

Room Name
Measurement Unit
Room Dimensions
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Window Type
Room Exposure
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    What is ΔDelta T50℃ and ΔDelta T60℃?

    Delta T, which can be written ΔT, means 'difference-in-temperature'. The amount of heat a radiator will transfer to the room depends on the difference between the temperature of water in the radiator and the temperature of the room it is in.

    For example:

    • If the room is 20℃, and the water in the radiator is 70℃, this temperature difference will cause heat to transfer from the radiator to the room
    • If the room is 20℃ and the water in the radiator is 80℃, this greater difference will mean more heat is transferred to the room

    Calculating the heat output of a radiator therefore depends not only on the construction of the radiator, but also on the temperature of the room it’s in, and the water in the system. As we don’t know these exact figures, we use a standard assumption to compare different radiators.

    The two most common standards are ΔDelta T60, where we assume the average water temperature in the radiator is 60℃ hotter than the room, and ΔDelta T50, where we assume the average water temperature in the radiator is 50℃ hotter than the room.

    Using different standards will give different heat output values. We usually try to give both on our website, but it is important when comparing radiators to use the same Δ Delta T each time to ensure an accurate comparison.