What is a BTU and how do I calculate the quantity I need for my rooms?

BTU stands for British Thermal Unit and it is used to describe the power of heating and cooling systems. Firstly, when estimating the size of a radiator you should decide what  temperature you  require your room to be. The most common ideal centigrade temperatures for specific rooms in your house are displayed in the table below as guide:

Bedrooms - 15°c
Kitchens - 16°c
Stairways/Hall - 18°c
Sitting Rooms/Dining Rooms - 21°c
Bathrooms/WCs - 23°c

The second calculation is for the heat loss from your room. This calculation will take into account many factors i.e. the size of your windows, whether the room is North or South facing, the number of doors etc. 
An easy way to do this is to first calculate the cubic feet (volume) of the room (length times width times height). Then apply the following calculations to specific rooms:

Halls/Stairways/Kitchens - Multiply cubic feet by 3
Bedrooms - Multiply cubic feet by 4
Sitting Rooms/Dining Rooms - Multiply cubic feet by 5
Double glazing - Deduct 10%
North facing room - Add 15%
French windows - Add 20%

You now have the approximate output of any radiator in BTUs (British Thermal Units) for your room. If you want to calculate the exact BTUs it would be best to get this checked by your plumber, but this guide is ample for calculating the sizes of radiator you will require. If you have a large room it is worth considering more than one radiator to minimize the thermal gradient in one room.

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