The DuraVent W2-1820 wall vent length is designed to vent Categories II, III and IV special gas burning appliances. Belonging to the FasNSeal collection, it is made of AL29-4C stainless steel that extremely resists corrosion and cracking. This wall vent length has an inner diameter of 20-inches with 18-inches of length. It is UL listed and is backed by a limited lifetime warranty.For your ventilation needs, you can trust the DuraVent products as your solution. Find one that you need here at PlumbersStock.com.