Draught System
Draught means the force needed to draw.
With regard to the boilers the requirement is to provide an adequate supply of air to the furnace grate to maintain the proper combustion of fuel, to draw the resulting gases from the system and to discharge these flue gases from the chimney to the surroundings.
It requires a static pressure difference to be maintained at the grate which causes the flow of air and gases to take place.
This static pressure difference maintained is called boiler draught or in short draught.