The conventional boiler combustion draught system provides the mass of air for burning the fuel. It is a balanced draught design which comprises a forced draught (FD) fan pushing the combustion air under the grate and induced draught (ID) fan drawing the flue gas away from the combustion chamber. The over-fire system consists of a secondary air (SA) fan to induce turbulence for optimising the combustion and fuel feeder (FF) to force the fuel into the furnace through the feeder chutes and spread evenly on the grate.