The commercial series of built-in wall fans has been designed for flush fitting into external walls, fitting through most wall thicknesses using zinc coated metal telescopic wall liners. Installation is made simple in solid or cavity walls 155-300mm thick, or in walls up to 553mm thick using an extension sleeve.The extractor fan unit and internal grille are also available separately as they are designed to retro fit into most leading commercial wall fan liners, which minimises the need for making good and redecoration or removal of existing wall liners.The internal and external grilles are a single tough moulding. This greatly reduces vandalism and increases building security whilst only 23mm in profile. They have a 50mm flange for a smooth finish, which will blend unobtrusively into most backgrounds.