What is the benefit of the added air space in the middle of a type "B" vent?

The benefit of the added air space in the middle of a type "B" vent lies in its ability to decrease heat loss significantly compared to a standard single-wall vent pipe. The design of a type "B" vent features a double-wall system with an air gap between the inner and outer walls. This air space acts as insulation, reducing the temperature difference between the vent pipe and the surrounding air, thus minimizing heat loss as flue gases travel through the vent.

This reduction in heat loss is particularly important for efficiency, as it ensures that more of the heat generated by the combustion process is utilized within the heating system rather than being lost to the environment. Additionally, maintaining higher flue gas temperatures can help improve the draft, which is essential for proper venting of combustion products.

Improving airflow is also a function of the vent's design, but the primary advantage of the air space is the insulation effect that leads to decreased heat loss. While structural integrity is a consideration with vent design, the main function of the type "B" vent’s air space is related to heat retention and efficiency.