Which venting system type operates under positive static pressure to remove flue gases?

The correct answer is the forced-draft venting system. This type of system is specifically designed to operate under positive static pressure, which means it utilizes a fan or blower to actively push the flue gases out of the system. This forced movement of air helps effectively expel combustion byproducts and maintain the necessary airflow through the venting process.

In contrast, other venting systems operate differently. Induced-draft systems typically create a negative pressure by drawing flue gases out due to the action of a fan located in the vent stack. Natural venting systems rely on the natural buoyancy of hot gases to rise and exhaust naturally without mechanical assistance, thus not maintaining positive pressure. Power venting systems, while they do provide a method of removing flue gases and may include fans, aren’t specifically characterized by maintaining positive static pressure in the way forced-draft systems do. Therefore, the defining feature of the forced-draft system being under positive static pressure is what makes it the correct choice.