🔍 Key Concepts

• heat transfer between hot combustion gases and boiler tubes • difference between fireside (gas side) and waterside (water/steam side) fouling • how combustion efficiency and excess air affect stack temperature

💭 Think About

• Think about what would cause more heat to be absorbed into the water/steam instead of going up the stack as hot gas. • Consider which type of fouling (fireside vs waterside) acts like insulation on the gas side, and how that would change measured stack temperature. • Ask yourself: if combustion were incomplete or fuel sulfur was high, would that primarily change temperature, or would it change something else first (like flame quality or corrosion)?

✅ Before You Answer

• Be clear on which surfaces the stack temperature sensor is actually measuring (gas side, not water side). • Decide whether extra insulation on the gas side would make the gas leaving the boiler warmer or cooler at the stack. • Consider whether incomplete combustion and fuel sulfur content have a direct, predictable effect on lowering stack gas temperature, or if their main effects are different (e.g., soot, corrosion, emissions).