How far must a mechanical draft venting system terminate below an operable window?

A mechanical draft venting system must terminate at least 4 feet below an operable window to ensure safe and effective venting of exhaust gases. This distance is crucial to prevent the backdraft of combustion gases into the building, which can pose health and safety risks, including carbon monoxide poisoning. The 4-foot requirement serves as a regulatory standard that helps maintain clear airflow and minimizes the risk of a hazardous situation, especially during windy conditions when exhaust may otherwise be pushed back toward the building.

In relation to the other potential distances, they do not provide the same level of safety against backdrafts. A termination distance shorter than 4 feet may not adequately safeguard operable windows, increasing the risk of harmful gases entering the living space.