Abstract: A burner pumps fuel through a fuel line and pumps air into a chamber. Air from the chamber and fuel from the fuel line enter a mixing chamber. The fuel and air mixture flow through an evaporator tube which extends into a combustion chamber and turns at two successive 90.degree. angles and releases the mixture in an opening facing the bottom of the chamber. Combustion air flows through the air chamber outward parallel to the combustion chamber walls in a labyrinth and then into an expansion chamber through air slots and past flow directing wings which give the combustion air a screw direction. Exhaust gas flows outward around the outer walls of the labyrinth. The evaporator tube has an outer area to inner volume ratio of 0.3 to 0.8.