Usually, the larger the radiator the higher the BTU. However, you could also select a radiator that has a second panel or layer. This second layer can significantly increase the amount of heat given whilst maintaining the stylish look of the radiator.
Traditional White Victorian Designer Horizontal Column Radiator 300 x 988 mm
Green Tea Architects - Side Return Extension, Brockley, London Colour Brick Cosmetics say - This property’s extension has been brick matched well but if thats not possible, for a variety of reasons, tint it so it does