What is the construction characteristic of Type B vent pipe?

Type B vent pipe is specifically designed for venting gas appliances that use flue gases. This type of vent pipe is characterized by its two-layer construction, which typically includes an inner aluminum layer and an outer layer made of galvanized steel. The aluminum layer is resistant to corrosion and is able to withstand the heat produced by gas appliances, while the outer layer provides additional structural support and durability.

The use of aluminum for the inner pipe is critical because it ensures safe venting of the flue gases while maintaining proper exhaust flow. This construction minimizes the risk of buildup of harmful gases and helps maintain the efficiency of the appliance.

In contrast, the other options listed do not accurately describe Type B vent pipe. Single-layer constructions lack the necessary insulation and structural integrity for gas venting, while flexible venting systems and PVC materials do not meet the required safety standards for high-heat applications like those encountered with gas heating appliances.