A combustion chamber in which oil is the heat-producing fuel. Fuel oils, having from 18,000 to 20,000 Btu/lb (42 to 47 megajoules/kg), which is equivalent to 140,000 to 155,000 Btu/gal (39 to 43 MJ/liter), are supplied commercially. The lower flash-point grades are used primarily in domestic and other furnaces without preheating. Grades having higher flash points are fired in burners equipped with preheaters. The ease with which oil is transported, stored, handled, and fired is advantageous in small installations. The fuel burns almost completely so that, especially in a large furnace, combustible losses are negligible.