3.10.1.1 ‘Hole-in-the-wall’ Installations. It is recommended that a hearth should be installed as in figure 4. If a hearth isnot fitted, the fire must be installed so that the distance from the base of the fireplaceopening in the wall to the finished floor level is at least 85mm. Where there is no floorcovering or carpet and the floor is of a type that is likely to be covered in such a waythen the distance from the base of the fireplace opening in the wall to the finishedfloor level should be increased to at least 160mm. To protect from the risk of burns and ignition of clothing a tactile separator shall beused. The hearth detailed in section 3.8 meets the requirements for a tactileseparator. If this is not used then a 672mm long fender, kerb, horizontal bar, or otherbarrier, being fixed not less than 50mm above floor level and positioned 300mm infront of the fixing plane of the fire will meet the requirement.3.10.2 Metal flue box and hearth.To a fireplace incorporating a metal flue box complying with the constructionalrequirements of the current edition of BS715. The dimensions of the flue box mustconform to those shown in figure 6.The whole of the top surface of themetal flue box must be covered witha 100mm layer of mineral wool orequivalent insulation (See figure 6).Important Note: Where the flue boxhas a base sheet that is single wall(i.e. a single metal sheet) the fluebox must be mounted on a non-combustible hearth. The hearthmaterial must be at least 12mmthick.Page 15© Baxi Heating U.K. Limited 2009.INSTALLER GUIDEFigure 6. Metal flue box