PURPOSE: To prevent incomplete combustion and improve the workability in fire extinguishing work by a method wherein an air duct is equipped with an air flow regulating device, and a ventilation hood is provided with a lifting device which brings the hood apart from and in contact with a fireplace unit and an exhaust gas flow adjusting device which regulates line flow of exhaust gas from the hood.

CONSTITUTION: An air duct 17 has an air flow regulating device 5. Thereby, an ample amount of oxygen is always supplied into a furnace chamber 10. As a ventilation hood 2 is provided with a lifting device 7 which moves the hood 2 up and down and an exhaust gas flow adjusting device 6, the furnace chamber 10 can be closed tight by lowering the hood 2 to cover the furnace chamber 10 and manipulating the exhaust gas flow adjusting device and the air flow regulating device 5 to block the exhaust gas flow and the air flow. Therefore, the workability in fire extinguishing work can be improved.