Patent ID: 6945196

Claim:
A water heater comprising an upright thermally insulated cylindrical water tank ( 1 ) with a lower wall ( 1 a ), an exhaust flue ( 3 ) extending axially and centrally through the water tank, a combustion chamber ( 2 ) arranged under the lower wall ( 1 a ) and connect to the exhaust flue, an atmospheric gas burner ( 5 ) in said combustion chamber and a complete pre-mixing gas/air supply system for the atmospheric gas burner, wherein said atmospheric gas burner comprises a burner mat ( 7 ) providing a combustion surface and said gas/air supply system has respective intakes for combustion gas and for combustion air arranged outside of the combustion chamber; wherein the gas burner ( 5 ) is attached to a wall section ( 2 a ), the combustion chamber ( 2 ) has an outer wall (W) provided with an opening ( 2 b ), said opening ( 2 b ) being partially closable by said wall section ( 2 a ) so that a gap of a predetermined width is provided between the wall section ( 2 a ) and the outer wall (W), and the gas burner ( 5 ) is releasably mounted in the combustion chamber ( 2 ) with the wall section ( 2 a ) by means of closure elements (C) that hold the wall section ( 2 a ) on the outer wall (W) over the opening ( 2 b ); and wherein the width of the gap is such that secondary air flows into the combustion chamber ( 2 ) through the gap but backfire of flames from the combustion chamber to the surroundings is prevented; and wherein said burner mat has a porosity such that a pressure drop across said burner mat ( 7 ) is in a pressure range of less than 5 Pa up to 45 Pa.