Supco number ECAP321 PVC Flue Pipe Rooftop Cap The patented new flue cap is designed to improve air flow and eliminate excessive moisture and debris that can rust or damage high efficiency gas furnaces, tankless hot water tanks, plumbing or other PVC vented installations. Material: GELOY CR7520 acrylic-styrene-acrylonitrile (ASA) resin, Dimensions: 5-1/2' O.D. x 3-5/8' High Precisely fits 1', 2', and 3' PVC pipe