DuraVent 3DFA-TP Top Plate. 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-TP Top Plate is designed for to seal the top of the masonry chimney. This Top Plate protects the masonry chimney from damaging effects that come with flue product condensation.