Abstract: A submerged combustion apparatus for heating a liquid including a liquid vessel that contains the liquid, a combustion chamber including a combustion chamber body, an inlet and a plurality of discharge ports, the combustion chamber body being positioned in the vessel so that at least the discharge ports are submerged in liquid in use, a burner that allows an air/fuel mixture to be burned at least partially within the combustion chamber thereby causing bubbles of heated gaseous combustion products to be emitted from the discharge ports so as to heat the liquid and a guide surface spaced apart from and extending along at least part of a length of a combustion chamber body outer surface so as to guide bubbles emitted from the discharge ports so that the bubbles are at least partially constrained to flow between the combustion chamber body outer surface and the guide surface.