The VFHB-F- series, vertical four pass F.B.C fired hot water boiler is designed for maximum efficiency, using a variety of free flow fuels including agro-waste fuels and pulverized coal. It allows required process temperatures at required operating pressures. The combustion system for free flow fuels consists of fuel feeding threw screw feeder handling and stoking equipment, in refractory lined chamber, air and flue gas handling system (including I.D. fan and F.D. fan) with blowers and pollution control equipment. The furnace construction is done on site (only for bricks works). It includes foundation, fabrication and erection of supporting structure, building up refractory chambers, fixing up firing doors, ash doors, access doors, air plenum chamber and air nozzle.