Many people, especially those who just bought their first fireplace-equipped home, completely ignore the existence of dampers, caps, and their use.
A chimney cap is a protective cap that is placed at the top of a chimney to protect it from weathering and damage. Chimney caps may be made out of metal, metal mesh, or firebrick. The caps are designed to direct rainwater away from the chimney, which will reduce damage and inhibit the formation of ice dams.
Chimneys that do not have a chimney cap can cause problems within the home. There is an increased risk for water damage in establishments with unsealed chimneys because moisture may become trapped between bricks or rocks. If moisture builds up, it could lead to spalling, which results when salt deposits corrode the bricks and make them fall off. Chimney sweep professionals recommend installing a metal mesh shield instead of a cement cap or placing firebrick on top of existing brickwork to prevent this type of problem.
Chimney dampers are a type of fire-resistance device that prevents backdrafts and keeps chimneys safe. The devices regulate the escaping of flammable products of combustion (mostly heat) to prevent fires or explosions. They come in many different shapes and sizes depending on the fuel source, age, design, manufacturer, application, and other related factors.
Chimney dampers are used in wood burning appliances to prevent backdrafts and help extend the life of the appliance. Dampers on oil furnaces work similarly to control the escape of heat, but also regulates the air intake. The most common chimney damper is circular, made of metal wire with clips at each end that open or close it allowing airflow.
A modern chimney damper has a gasket with hygroscopic properties that closes with changes in humidity levels, it also opens when temperatures drop below an acceptable range for closed position. Some dampers are based on solenoid mechanisms activated by thermostatic switch to operate during certain weather conditions or when oxygen levels fall below predetermined parameters.