These are two completely different venting systems designed for different types of appliances and they cannot be mixed or swapped. Wood burning chimney pipe, such as the 8DM, 8HT, 12DM, and 12HT series in our collection, is used for wood burning fireplaces, wood stoves, and high-heat appliances. It is a double wall insulated pipe designed to handle extremely high flue temperatures and exhaust combustion gases safely up through the roof. Direct vent pipe, such as the DVL, DVP, and SLP series, is used exclusively for gas appliances like direct vent gas fireplaces. It operates as a sealed two-pipe system where one pipe exhausts combustion gases out and the other draws fresh combustion air in from outside, making it airtight and safe for indoor use.