More damage is caused by the lack of a chimney cap than from any other source.
Rain causes premature deterioration to the chimney interior and can rust metal fireboxes and dampers. It can erode flue tiles and mortar joints, causing them to crumble and leave dangerous cracks and blockages. Chimney caps protect your chimney from the elements. They also protect from birds and animals and the variety of diseases-such as rabies and histoplasmosis- they bring with them. Nests can cause dangerous flue blockages. Chimney caps also reduce the danger of roof fires caused by flying embers.