Differences between FD Fan and ID Fan

FD Fan	ID Fan
Forced draft fan	Induced draft fan
used basically for providing the required quantity of hot air to the furnace for smooth and uniform combustion of fuel	Located between dust collector and chimney
FD fan will supply required air for the combustion of the fuel in the furnace	ID fan will take the hot flue gases from furnace and will deliver to chimney.
FD fan will produce the positive pressure inside the system i.e. furnace	ID fan will produce the negative pressure in the furnace to remove the flue gases
Handle cold air	Handle hot gas, hence more power is required
Less maintenance , consume less power as density of cold air is less.	Cope with corrosive combustion products and fly ash
Is much smaller than ID fan.	Size is largest as it exhaust all air (secondary air and primary air) and is first to start as is necessary for safe boiler operation to prevent pressurization of boiler.