What is the role of a fan in a Category 4 venting system?

In a Category 4 venting system, the role of a fan is primarily to remove flue gases from the system. This type of venting system is designed for high-efficiency appliances, which often operate with a sealed combustion system. The fan facilitates the forced expulsion of combustion gases from the appliance to the outside environment.

Category 4 venting systems are distinct because they may use a fan to create negative pressure within the flue assembly, ensuring that combustion products are safely vented away from the appliance and reducing the risk of backdrafting. Additionally, because they operate with a lower exhaust temperature and often utilize PVC or CPVC piping, the proper removal of flue gases is crucial for maintaining safety and efficiency within the system.

The other options relate to functions that do not align with the specific role of the fan in this context. Circulating air within the furnace, for example, pertains more to the operation of the furnace itself rather than the venting system. The notion of pressurizing the venting system does not apply as most Category 4 systems utilize negative pressure to effectively discharge gases. Enhancing heat exchange is also not directly related to the venting system's primary function of ensuring safe flue gas removal.