PURPOSE: To make it possible to prevent a compulsory force from being applied to a double tube ceramic outer pipe and to effectively absorb the thermal expansion of the outer tube and to perform the spring adjustment with a stable posture by suspending an inner tube from the upper part of a flue through a spring, and supporting the lower end of the inner tube at the lower end of the inner tube.

CONSTITUTION: A suspension rod 21 is provided in upwardly projecting manner at the tip end of the copper inner tube 2, and a support pipe 30 concurrently used as a packing keep is loosely fitted in a rod 21 and the main body of the inner tube 2. On the support tube 30, a spring seat 31, a helical spring 3 and a spring seat 32 are loosely fitted in the rod 21. At the tip end of the rod 21 is fitted a nut 23 to define the upward movement of the spring 3. At the lower end of the pipe 2 is provided a reversing brick support metal fitting 25. The ceramic outer tube 1 is supported from the lower side from an engaging part 250 of the lower end of the metal fitting 25.