A balanced draught boiler furnace employs __________ draught fan.

ANS:C - both 'a' & 'b'

A balanced draught boiler furnace employs both induced and forced draught fans. In a balanced draught system, both induced and forced draught fans are used to maintain the desired pressure inside the furnace.

• Induced Draught Fan: The induced draught fan is placed at the outlet of the boiler or furnace and creates a negative pressure (vacuum) inside the furnace, which helps in the efficient removal of flue gases from the combustion chamber.
• Forced Draught Fan: The forced draught fan is positioned at the inlet of the boiler or furnace and supplies air under pressure into the combustion chamber, aiding in the combustion process by ensuring sufficient oxygen supply to the fuel.

By using both induced and forced draught fans, a balanced draught system can maintain control over the airflow and pressure within the furnace, optimizing combustion efficiency and minimizing heat loss through the flue gases. Therefore, the correct answer is both 'a' & 'b'.