a chimney damper for round flues that includes a rigid peripheral frame surrounding an open window area , a cap moveable toward and away from the open window to selectively close and open the same and springs interconnecting the cap and frame resiliently urging the cap to an open position . the square , rectangular , or round frame includes a shirt adapted to form or connect to a cylindrical base which comprises a round open window and thus can be configured for use on a round flue . the springs are preferably torsion springs and are located within the cap assembly and the open window area defined by the peripheral frame . the cap is guided during its movement toward and away from the frame by the springs and during such movement the cap rotates a partial turn relative to the frame to which it is connected by the springs .