Abstract: A compact and modularized boiler is comprised of interconnected modules. h module is removable and replaceable with an identical module for easy on site repair. The modules are separated physically and in function as a supercharger module connected to provide compressed air; a burner module connected to receive fuel and compressed air for combustion; a furnace module housing a combustion chamber for receiving hot gas from the burner module and water to be heated from a pump module; a steam drum module for separating liquid and steam; a superheater module interfaced with the furnace module for generating superheated steam; and a convection module for providing additional surface area for heat transfer from the hot gas to the working liquid. The boiler is compact and modular.