Horizontal bars form the main design of the stelrad caliente creating a sleek and stylish look - perfect for bathrooms and living areas alike! It is always good practice to ask your heating engineer what size boiler he or she thinks best fits your requirements. Combi boilers from 24kw to 33kw, straightforward to install with easy to use controls. Advance spares manual december 2017.pdf. Does anyone know which electric boilers are good quality? we are.