🔍 Key Concepts

• Trace the gas flow path from the furnace to the stack in the illustration. • Identify where combustion air enters versus where flue gases leave the boiler. • Recall what a regenerative air heater looks like compared with simple ducting or openings.

💭 Think About

• Look at arrow B and ask: does this passage seem to be carrying incoming fresh air or outgoing hot gas? What visual clues support your thinking? • Compare the component at B with the path leading from the forced-draft fan (I) and with the path leading toward the stack/outlet. Which system is it aligned with? • Which of the options would normally be a large external duct on the top/side of a boiler, and which would be smaller openings or rotating equipment?

✅ Before You Answer

• Verify whether the space indicated by B is inside the pressure part (tube bank area) or an external duct attached to the boiler casing. • Check if there is any sign of a rotating element or sector plates, which would be typical of a regenerative air heater. • Confirm that a retractable sootblower opening would usually appear as a relatively small nozzle or port near tube banks, not as a large duct.