Most masonry chimneys are built with bottom sealing dampers. These dampers are usually made of cast iron and are subject to corrosion & rust – causing them to freeze up & become inoperable. Typically, these types of dampers are not very efficient in keeping out the weather, hot/cold drafts, etc. A top sealing damper is much more energy efficient, and is installed to the top of your existing clay tile liner. It is easily operated by pulling a simple cable to open & close the damper.