A design and method of operation for the floor of solid fuel boilers is described. The combustion region includes a stepped-floor that improves combustion in the lower furnace. In some embodiments, the fuel is moved between the steps of the floor by a gas, rather than by mechanical means, and the fuel is moved from an upper to a lower step as it is burned. In some embodiments, the steps are fixed steps having a layer of a refractory material.