Essar Enviro Air Systems is a top leading FD Fan Manufacturer of Industrial Fans and Blowers. Before discussing the differences between ID and FD fan, first we need to understand why draft systems are required and its uses for the industrial applications. Basically, a Draft System is required for 2 main reasons. Providing required quantity of hot air to furnaces for smooth combustion of fuel. Removing the flue gases from a system that is furnace to the atmosphere after filtering dust through electrostatic precipitators.