What distinguishes an induced draft system from a forced draft system?

The distinction between an induced draft system and a forced draft system lies in the position of the fan relative to the heat exchanger and the flow of combustion gases. An induced draft system is designed to pull combustion gases out of the heat exchanger and into the exhaust system, which means that the fan operates at the combustion appliance's exhaust side, creating a negative pressure that draws air and gases through the system. This configuration effectively ensures that combustion gases are expelled from the system safely.

In contrast, a forced draft system relies on a fan installed at the intake side, pushing air into the combustion chamber to aid in the combustion process. This setup establishes a positive pressure in the combustion area, which can help ensure that sufficient air is available for burning the fuel efficiently.

The correct answer highlights that induced draft processes occur at the end of the heat exchange and combustion cycle, allowing for effective exhaustion of gases. This principle is critical for maintaining safety and efficiency in heating systems, illustrating the significance of how each draft system operates within its structure.