What is the primary function of a vent damper in a warm air furnace?

The primary function of a vent damper in a warm air furnace is to reduce the heat lost up the chimney when the burner is off. When the furnace is not operating, a vent damper closes the flue, preventing warm air from escaping and cold air from entering the system. This helps maintain efficiency by minimizing heat loss, ensuring that the furnace operates more effectively when it is turned back on. Keeping heat contained when the system is idle directly contributes to energy efficiency and can lead to lower heating costs.

While other options describe functions that might seem relevant, they do not accurately reflect the primary role of a vent damper. For instance, continuous air circulation is not managed by a vent damper, as it is more about the overall airflow system. Additionally, while air filtering can be important for air quality, it is typically not a function associated with the vent damper. Similarly, increasing heating speed is not the purpose of a vent damper; its role is more about heat conservation rather than directly influencing the heating rate of the furnace itself.