Design With its many successful innovations, Zehnder Group – the inventor of the steel radiator – has been the leader in the radiator industry for 70 years. Most of the radiator models available on the market today have, in some way, drawn on a Zehnder Group innovation. It's many patents and proprietary models bear witness to the group's innovative spirit, and the numerous design awards show the high regard Zehnder Group's products enjoy at international level.