Abstract: An automatic mechanical flue fire extinguishing system includes a pressurized container of fire-extinguishing material which communicates with a thermally sensitive valve installed in a flue pipe of a wood stove or the like near the bottom of the flue pipe. When a predetermined temperature is reached, a fusible metal disk within the valve melts, opening the valve and releasing the fire extinguishing material into the flue pipe, thereby extinguishing the flue fire. The fire extinguishing system may also be manually operated.