Abstract: The inner wall of a combustion chamber is composed of a plurality of ceramic plates which are suspended from the outer wall of the chamber by being hooked over mounting portions of the outer wall; this eliminates the need for screws, bolts, welds or the like and facilitates mounting and dismounting of the plates. The plates define with the outer wall a clearance into which cold air is admitted; the upper and lower edges of adjacent plates define with one another respective air gaps communicating with this clearance so that air streams enter the combustion space through these gaps. These air streams prevent the deposition of ash and other contaminants on the inner surfaces of the plates.