What type of draft is employed to move flue gas through the heat exchanger and into the venting system in modern gas-fired furnaces?

In modern gas-fired furnaces, a mechanical draft is utilized to efficiently move flue gas through the heat exchanger and into the venting system. This system often employs a fan or blower designed to create a controlled and consistent airflow, which enhances combustion efficiency and ensures that any harmful exhaust gases are safely expelled from the home.

Using mechanical draft allows for better control over the combustion process, as it can adapt to changes in pressure and airflow conditions. This is especially important in high-efficiency furnaces that may operate at lower temperatures, potentially reducing the natural draft effect. The mechanical system ensures that exhaust gases are effectively pushed through the vents, reducing the risk of backdrafts or incomplete combustion.

In contrast, natural draft systems rely on buoyancy and the natural rising of hot gases, which can be influenced by environmental conditions and may not effectively handle the performance needs of modern heating systems. Draft inducers are typically used in conjunction with other systems to enhance draft but are not the primary source of moving gases in the furnace operation, while combination draft systems may include both natural and mechanical methods but are not standard in modern gas-fired furnace applications. Thus, mechanical draft stands out as the most suitable and effective means for venting in contemporary gas furnace design.