The Radiator BTU Calculator

Published: 21 Mar 2022 ・ Read time: 4 mins
When choosing the right radiator for your system to ensure your property is being heated up efficiently, it is arguably as important to consider the correct BTU as it is the design, style or finish.
The BTU rate of a radiator is a quick and easy way of letting you know how much heat a radiator will emit and is there to help you decide if a radiator is the correct size for your room or not. It is important to know exactly how much heat each room your property needs, in order for your system to work efficiently and to have a space that is neither too hot nor too cold.

What is BTU?

BTU stands for British Thermal Unit. A BTU is the measurement used to represent the amount of energy needed to heat one pound of water (roughly a pint) by one degree fahrenheit at sea level. BTU is the standard measurement when it comes to choosing the radiator size and style. As such, BTU provides a quick reference for the radiator output.
It is worth it to correctly calculate the BTU value needed to heat up a room. Too little BTU output and the room won’t rise to the required temperature and the room will be cold and uninviting. Too many BTUs and you could find yourself paying over the odds for heat that you don’t need.

BTU Calculator

In order to work out the BTU needed for a specific room you can use our handy Heat Loss Calculator. This radiator size calculator will help you find the correct radiator BTU output for your room. When working out the BTU of a room there are a few things that you need to remember.
  • Measure your room - Work out the square metre area of the room in order to be accurate with the amount of heat you will need. Our calculator does this work for you, as you only need to include the height, width and length of the room.
  • Count the windows in that space - It is important to factor in the number of windows there are in the space. Draughts will contribute to the final BTU number. Within the calculator that is included as a total window area in square metres.
  • Count the radiators you'll need - Do you need one, two, three or maybe even more radiators to make the most of your central heating. The calculator will provide a total BTU value for the room and this needs to be divided however you like between enough radiators to heat up the room.
  • Know what is above and below the room - Knowing what is above and below the room will make a big difference to the final BTU number. Solid floors retain heat differently to a floor with a cellar or a cavity.
  • Know what is on the other side of each wall of the room - As with the floor and ceiling, what is on the other side of the wall and what the wall is made of, will play a big part in the radiator size you choose.

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