Selkirk® by Duravent DWC double wall flexible gas vent pipe is available in 3, 4 and 5 in Dia in 2, 3, 4 and 5 ft L designed for easy connection to standard type B gas vent. DWC is listed for use as a "segment" of an unenclosed type B gas vent system and is fully safety certified for use in conditioned and/or unconditioned attics and crawl spaces. DWC can simplify alignment of most installations by enabling a quick and easy offset between sections of rigid gas vent.