An electrical heater for heating liquid containing at least one scale forming element and methods for fabrication and use of the heater are described. The electrical heater comprises a heating unit including electrical resistance heating material, and a heat conducting sheath disposed over at least a portion of the heating unit. The heater also includes a pair of terminal ends extending from the electrical resistance heating material for connecting the heating unit to an external source of electric power. The heat conducting sheath includes an electrically insulating compound that features anisotropic heat conductivity with enhanced transparency to infra-red radiation along axes normal to a surface of said electrical resistance heating material.