Fuel boilers refer to boilers that use fuel oil as their fuel source, including diesel, waste oil, and other oils. The overall arrangement of fuel boilers is similar to that of coal-fired boilers, but the furnace bottom of fuel boilers is often tilted backward towards the wall at an angle of 10° to 30° for insulation, to achieve good combustion characteristics. To enable the fuel oil to atomize, there are two types of oil burner nozzles: mechanical centrifugal nozzles and steam atomizing Y-type nozzles.

Fuel boilers include fuel water boiler, fuel hot water boiler, fuel heating boiler, fuel bathing boiler, and fuel steam boiler, etc. Fuel boilers refer to boilers that use light oil (such as diesel oil, kerosene) and heavy oil, and residue oil as fuel. Compared with electric heating boilers and gas boilers, fuel boilers are more cost-effective than electric heating boilers and more convenient to use than gas boilers.