prevents the re of the exhaust gases; facilitates the suction effect; improves the combustion; protects the Chimney of outer influences such as rain or snow .. Select the size based on the outer diameter of your tube. The rotor ball already turns with minimal wind and is not just a real eye-catcher on your roof, but also offers excellent properties .. 304 Thick Stainless Steel Rotating Chimney Cowl Cap: Spinner Anti-Downdraught Fits Most Standard Chimney Pots Very effective in preventing wind and increasing ventilation. Rotating hood for ventilation pipes, chimneys, and air extraction.The gairing provides maximum protection without hindering the performance of the chimney.