How do i calculate the size radiator i need for my house?

Step 1 - Find the volume of the room in cubic metres: * Calculate length x width x height Step 2 - Adjust according to room type: * Lounges and dining rooms multiply by 50

* Bedrooms multiply by 40

* Common areas and kitchens multiply by 30

* Bathrooms multiply by 90

Step 3 - Allow for important variables: * For rooms facing north add 15%

* For French Windows add 20%

* For double glazing deduct 10%

* For very exposed sites, or very cold weather add 10%

* For new builds (that are much better insulated) deduct 20% This will give you the output of any radiator in watts.Multiply this by 3.412 to give the BTU requirement for the room.