Abstract: An integral water-cooled, air permeated, vibrating grate system for combusting biomass and other fuels in a boiler includes a grate top surface having air-flow apertures extending therethrough. The grate top surface is supported by a plurality of water-cooling pipes which arc coupled to a water supply. An enclosed air plenum unit is positioned under and attached directly to the grate top surface. The air plenum unit is coupled to an air supply for providing combustion air through the top grate surface air-flow apertures. The air plenum unit includes multiple zones, each of which zones has an associated air flow control damper so that the flow of combustion air can be controlled. Ash siftings formed on the grate top surface when the biomass or other fuel is combusted fall into the air plenum unit and flow toward at least one ash-siftings discharge opening at a discharge end of the air plenum when the grate top surface and the air plenum is vibrated.