The grate is supported in raised, operative position by a raising and lowering mechanism. For cleaning, the grate is lowered onto track rails in an air chamber below the grate. By opening a door in the furnace air jacket the grate may be pulled out onto exterior track rails for cleaning. The grate is equipped with a water cooling coil and flexible hose connections which accommodate travel of the grate into and out of the furnace without disconnection of the water supply. When the grate is pulled out of the furnace it disengages from the raising and lowering mechanism and when rolled back into the furnace it reengages with the raising and lowering mechanism and is lifted to operative position. Instead of cleaning the grate immediately and returning it to the furnace, it may be replaced with a cleaned grate in order to get the furnace back into operation more quickly.