Class B pipe is a venting system capable of handling the exhaust from appliances that burn propane & natural gas with temperatures up to 470 degrees continuous and operating under a natural draft. Despite the double wall construction the outside shell of this pipe still gets hot and requires an air space. The metal used on the outside is galvanized steel and the metal used on the inside is aluminum. Lengths range from 6″ to 60″ and diameters range from 3″ to 8″. We supply & install these products.