Burner has parallel vertical supply ducts (1, 2) for the two combustion components (gas and air). A first one (1) of said ducts opens upwardly at a first outlet (3) which is substantially oblong in plan view and the second (2) of said ducts opens at a plurality of second outlets (5a, 5b) which are located on either side of and above the first outlet (3), the general discharge directions of the second outlets, (5a, 5b) being oblique to that of the first outlet (3).;The first outlet (3) has, as seen in plan view, a slot shape and has, in its long sides, a plurality of recesses (8) which extend outwardly towards the second outlets (5a, 5b). The second outlets (5a, 5b) are arranged alongside the said long sides of the first outlet (3) with the second outlets (5a, 5b) on one side opposite those on the other side. The recesses (8) are, along the length of the first outlet (3), located alternately in said long sides and, on each said long side, directed towards alternate ones (5b) of said second outlets (5a, 5b).
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