American Metal Cap Gas Vent 3in Double Wall The AmeriVent cap is the first engineered vent cap to gain recognition across the country for its performance Millions of them are now installed on homes and business structures to protect against wind conditions that can cause waste gases to spill back into the structure through the appliance draft hood The AmeriVent cap is UL-listed, and its patented design of ports and baffles keep rain and debris out of the vent AmeriVent caps permit termination of vents at the minimum height necessary above the roof surface The AmeriVent Cap is used as a ventilation cap as well as a type B gas vent termination