The burner for gas or oil has a central jet (8) set inside the Venturi duct formed by a converging section and a diverging section. The Venturi is followed by a cylindrical burn chamber (18) whose length is at least three times its diameter. The hollow ring duct (5) formed between the sloping walls of the Venturi and the cylindrical burner draws in exhaust gasses via holes (3,4) in the outer wall. These gasses enter the burn chamber via holes in the diverging wall of the Venturi. The Venturi is movable to control the aperture of the exhaust gas recycling holes (3,4). A bi-metallic strip valve (6) controls the exhaust gas outlet holes into the burn chamber with the valves shut during cold start-up.
