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.
Arche-Plus Radiator in horizontal and vertical configurations. Like many of the radiators shown here, it can also be outfitted with towel rails, towel rings, and robe hooks. In the US, the Vasco Arche line is available through Hydronic Alternatives.
Founded in Swiss company Runtal touts its combination of engineering expertise and architectural design; its Runtal Arteplano Radiator is shown here in anodized aluminum. Contact Runtal USA for specifications and pricing.