The Vacu-Stack VSS is made to fit solid pack Class A, Masonry, or Single Wall Chimneys. Stop Down Drafts and Smoking Caused From: Mountain winds in homes near slopes Wind deflected by tall trees Erratic, turbulent wind around buildings or other obstructions Appliances vented through the sides of buildings The Vacu-Stack VSS is made of 304 stainless steel and is available in 3" - 10" round diameters. To install, simply slide the Vacu-Stack VSS (with the spring fit design) into the pipe. Most of the wind-related down draft issues will be greatly improved when using the Vacu-Stack. Non wind-related problems may also see improvement when using the Vacu-Stack, but may not completely cure the issue. The Vacu-Stack also performs as regular rain cap protecting againt debris, snow, rain and critters. If the Vacu-Stack has been installed it may not be returned.