What is a characteristic feature of type BW-vent?

Type BW-vent is specifically designed for gas-fired appliances, which includes wall furnaces and is crucial for safely venting combustion gases produced during the operation of these appliances. It features a double wall construction that provides insulation, reducing heat loss and improving safety. This design helps to prevent the outer wall from becoming too hot, minimizing the risk of fire hazards.

While there are various vent types suited to different appliances, the BW-vent's unique construction and intended application for gas-fired systems make it the right answer in this context. Other options, such as those related to oil-fired appliances, single wall structures, or materials like copper, do not accurately describe the characteristics and intended use of type BW-vent.