A boiler is a shut vessel in which liquid (by and large water) is warmed. The liquid does not really bubble. The warmed or vaporized liquid leaves the boiler for use in different procedures or warming applications, including water warming, focal warming, boiler-based power age, cooking, and sanitation.

In a non-renewable energy source control plant utilizing a steam cycle for power age, the essential warmth source will be burning of coal, oil, or petroleum gas. Now and again side-effect fuel, for example, the carbon-monoxide rich offgasses of a coke battery can be scorched to warm a boiler; biofuels, for example, bagasse, where financially accessible, can likewise be utilized. In an atomic power plant, boilers called steam generators are warmed by the warmth delivered by atomic splitting.

Where a substantial volume of hot gas is accessible from some procedure, a warmth recuperation steam generator or recuperation boiler can utilize the warmth to create steam, with next to zero additional fuel expended; such a setup is basic in a consolidated cycle control plant where a gas turbine and a steam boiler are utilized. In all cases the burning item squander gases are independent from the working liquid of the steam cycle, making these frameworks instances of External ignition motors.