The Precision Model FPW Vertical Firetube Water Heater features the traditional firetube design in the vertical configuration with an under-fired power burner. In addition to the simplicity of the 4-piece design, the Model "FPS" includes many advantages over other vertical configured boilers such as larger water volume and steam chest which reduce cycling and improve overall efficiency, easier sludge cleanout, standard "off-the-shelf" burners, and the proven firetube reliability. An integral feedwater preheater eliminates "cold water shock" problems characteristic of some fixed tubesheet designs.