An appliance vented by natural draft must not be connected to a vent on which side of a mechanical flue exhauster?

The correct answer is the discharge side of a mechanical flue exhauster. When dealing with appliances vented by natural draft, it is essential that they remain on the intake side of the exhauster. This is crucial for ensuring that the natural draft is not compromised.

Natural draft relies on the natural buoyancy of hot gases, where the warm air rises and creates a negative pressure that pulls in combustion air. If a natural draft appliance is connected to the discharge side of a mechanical flue exhauster, it could disrupt the proper functioning of the natural draft. The mechanical flue exhauster is designed to actively push flue gases out, and connecting natural draft systems to this side could lead to improper venting, backpressure, and possible introduction of flue gases into the living space.

Maintaining the integrity of the natural draft system is essential for safety and efficiency, which is why it must not be connected on the discharge side. Connections on the intake side, on the other hand, are appropriate because they would not interfere with the operation of the natural draft.