Which component acts as a barrier between hot combustion gases and circulating air in a furnace?

The heat exchanger is the component that serves as the crucial barrier between hot combustion gases and the circulating air within a furnace. Its primary function is to transfer heat from the combustion process to the air that is being heated for distribution throughout the living spaces. By doing this, it ensures that the heated air can be utilized for warming the home while preventing the potentially harmful gases produced during combustion from entering the air supply.

The design of the heat exchanger allows it to efficiently separate the two environments—the combustion gases on one side, and the clean air intended for the living space on the other. This separation is vital for maintaining indoor air quality and safety, as combustion gases can contain harmful substances. Thus, the heat exchanger not only facilitates heating but also provides a protective barrier that enhances the overall safety of the HVAC system.

In contrast, the other components listed serve different functions within the HVAC system. Air filters are primarily meant to remove contaminants from the air before it enters the heating or cooling system. The evaporator coil, on the other hand, functions in the cooling cycle of the system, absorbing heat from the air, whereas the vent connector pipe is designed to safely exhaust combustion gases outside, rather than providing a barrier for heat exchange.