A chimney cap is a cover shaped hood that fits over the top of a chimney. The caps are usually made of aluminum or galvanized iron steel. The main objective of installing a chimney cover is to prevent downdrafts, but is also made to prevent other elements undesirables from entering the home through the chimney.
The chimney caps are designed to provide ventilation for smoke and gases into functional fireplaces, but also used in fireplaces out of service as caps to prevent birds, squirrels, bats and other nuisance animals build their nests there. The cowls also act as protectors of the rain to prevent moisture in your fireplace, and sometimes designed with a wire mesh barrier to stop the escape of sparks on your roof and provide a barrier against insects.
The appropriate cap for your chimney depends on whether the fireplace is in use, and if it is, the source of fuel used. The vent caps, for example, prevent condensation and chimneys are commonly used to down. The solid caps and fuel gas vented smoke from fires gas and solid fuels, such as coal or wood. The oil caps are for use with the fires of oil and multipurpose hoods can be used with most types of fuel. Except for the multi caps, each is designed for use with a specific type of fuel. A cap designed for use with burners that use fuel oil, for example, should not be used to cover a gas burning fireplace.
A stationary cover fireplace is basically a cover that easily fits over your fireplace. It screws or tie in place and although it is used in active and functional fireplaces, is also ideal for covering chimneys that are not being used.
Rotary caps are similar in design to turbine ventilation and prevent air currents coming down in your fireplace. This prevents the smoke and flue gases from entering your home. The rotation is powered by wind or heat inside the chimney and results in a suction action draws the smoke and fumes up and out of the chimney.