Permanent chimney cowls
Permanent cowls use the kinetic energy of the wind to generate a vacuum in the chimney. They do not change their position relative to the blowing of air. They usually have a cylindrical shape of the letter "H" or star-shaped. They are used at the ends of ventilation ducts and flue gas.
You will also find in this section some permanent cowls with additional generating extra draught motor. These cowls are good for purposes where extra draught is required and no spinning cowls can be used due to lack if wind or lack of space.