Which of the following describes the purpose of a forced draft fan?

The purpose of a forced draft fan is to supply combustion air to the furnace. In a combustion system, adequate air is essential for the burning of fuel, as it ensures that the combustion process is efficient and maintains proper stoichiometric ratios. By forcing air into the furnace, the fan helps create the necessary conditions for optimal burning, which leads to better fuel economy and efficient heat generation. Additionally, supplying the right amount of air minimizes the production of unburned fuel and reduces excess flue gas emissions.

While other options might seem relevant in a broader context, they do not specifically address the main function of a forced draft fan, which is foundational to the combustion process in boilers and furnaces. For example, while reducing flue gas emissions might be an outcome of efficient combustion, it is not the primary purpose of the fan itself.