What function does a boiler's economizer serve?

A boiler's economizer plays a crucial role in improving overall efficiency by recovering waste heat from flue gases before they are expelled into the atmosphere. This recovered heat is then used to preheat the water entering the boiler, which can enhance the boiler's performance and reduce the amount of fuel needed to achieve the desired steam output or water temperature. By utilizing this waste heat, the economizer helps lower fuel costs and minimizes the environmental impact by improving the energy utilization of the boiler system.

In contrast, other options do not accurately describe the function of an economizer. While reducing the boiler's size and lowering steam temperature may be desirable in certain aspects of boiler design and operation, those actions do not reflect the primary function of an economizer. Additionally, increasing fuel consumption is contrary to the purpose of an economizer, which is designed to make the boiler operate more efficiently and reduce fuel usage.