A fuel burner comprising: an outer tube extending along a central axis and having an outer surface and an inner surface defining a passage; an inner tube (40, 40a, 40b, 40c, 40d) positioned within the passage of the outer tube and having an outer surface and an inner surface defining a central passage, the inner tube (40, 40a, 40b, 40c, 40d) extending from a first end to a second end, wherein a fluid passage is defined between the outer surface of the inner tube (40, 40a, 40b, 40c, 40d) and the inner surface of the outer tube, the fluid passage being supplied with a mixture of air and combustible fuel, the inner tube (40, 40a, 40b, 40c, 40d) having a fluid directing structure (52, 52a, 52b, 52c, 52d) with a plurality of openings (54, 54a, 54b, 54c, 136) for directing the mixture from the fluid passage to the central passage such that the mixture rotates radially about the central axis; an end wall is provided on the first end of the inner tube (40, 40a, 40b, 40c, 40d) and closing the first end of the inner tube (40, 40a, 40b, 40c, 40d) to prevent the incoming fuel/air mixture from directly entering the central passage of the inner tube; and a cap securing the second end of the inner tube (40, 40a, 40b, 40c, 40d) to the outer tube in a gas-tight manner, thereby preventing the air / fuel mixture from exiting the fluid passage in a manner other than through the openings (54, 54a, 54b, 54c, 136) in the inner tube, wherein the mixture of air and combustible fuel enters the outer tube at a first end of the burner in the direction along or parallel to the central axis to be delivered to the fluid passage and to continue to flow towards a second end of the burner. an outer tube extending along a central axis and having an outer surface and an inner surface defining a passage; an inner tube (40, 40a, 40b, 40c, 40d) positioned within the passage of the outer tube and having an outer surface and an inner surface defining a central passage, the inner tube (40, 40a, 40b, 40c, 40d) extending from a first end to a second end, wherein a fluid passage is defined between the outer surface of the inner tube (40, 40a, 40b, 40c, 40d) and the inner surface of the outer tube, the fluid passage being supplied with a mixture of air and combustible fuel, the inner tube (40, 40a, 40b, 40c, 40d) having a fluid directing structure (52, 52a, 52b, 52c, 52d) with a plurality of openings (54, 54a, 54b, 54c, 136) for directing the mixture from the fluid passage to the central passage such that the mixture rotates radially about the central axis; an end wall is provided on the first end of the inner tube (40, 40a, 40b, 40c, 40d) and closing the first end of the inner tube (40, 40a, 40b, 40c, 40d) to prevent the incoming fuel/air mixture from directly entering the central passage of the inner tube; and a cap securing the second end of the inner tube (40, 40a, 40b, 40c, 40d) to the outer tube in a gas-tight manner, thereby preventing the air / fuel mixture from exiting the fluid passage in a manner other than through the openings (54, 54a, 54b, 54c, 136) in the inner tube, wherein the mixture of air and combustible fuel enters the outer tube at a first end of the burner in the direction along or parallel to the central axis to be delivered to the fluid passage and to continue to flow towards a second end of the burner.