Mechanical draft systems must be at least how many feet away from any gravity openings such as windows and doors?

The requirement that mechanical draft systems must be at least 4 feet away from any gravity openings, such as windows and doors, is based on safety and efficiency considerations. This distance is established to prevent backdrafting, which can occur if there is an improper air flow caused by the mechanical draft system being too close to openings that can allow outside air into the building.

When mechanical systems are located too near windows or doors, there's a risk that exhaust gases from the appliance may enter the building instead of being expelled outside. Maintaining a distance of 4 feet helps ensure that the airflow patterns are adequate, preventing any recirculation of combustion gases into the living spaces. Moreover, this distance aids in promoting proper ventilation, which is essential for the safety of occupants and the efficient operation of the mechanical draft systems.

Considering these factors, it's clear that the specified distance enhances both safety and operational performance, which is essential in any natural gas installation.