DuraVent 3DFA-VC Vent Cap. DuraVent is a leader in the venting industry. DuraVent has a large line up of venting products and continues to design safe and efficient venting part and products. This DuraVent 3DFA-VC Vent Cap is designed for Chimney Gas Liners. This Vent Cap is ideal for efficient air ventilation. The dome shaped cap prevents any form of precipitation from entering the ventilation systems.