It is important to use anti-downdraft chimney cowls when your chimney is exposed to windy conditions and the wind creates drafts and eddies, causing smoke to blow down the chimney and into your home.
In addition to wasting heat, unused chimneys can cause damp problems, as well as make fireplaces and stoves smoke. There should be a flue ventilator installed on any chimneys that are not used.
It is possible to prevent rainwater from entering the flue by using rain caps, hooded cowls, and wind-directional cowls. In order to ensure adequate protection against rain and other elements, it's important to select the right cowl for your chimney.