a frame element for forming a grate , including two spaced - apart side members and several plate members arranged one next to the other between the side members in longitudinal direction thereof , between which plate members is provided a gas - venting slot . the side members are formed by two opposing surfaces of a rigid frame , and the plate members are each constructed as individual structural parts releasably connectable to the side members . the plate members are preferably inserted one after the other into longitudinally extending guideways arranged on the frame and are spaced apart by spacing projections , the spacing being necessary to form a gas - venting slot .