🔍 Key Concepts

• combustion air flow patterns in an oil‑fired water‑tube boiler • effect of cool secondary air leaks entering around the furnace or gas path • relationship between gas temperature and boiler efficiency/tube heat transfer

💭 Think About

• Picture where the inner casing is in relation to the burner flame and gas path—does leaking air go into the water/steam side or the gas side? • If relatively cool air sneaks into the hot gas stream, what happens to gas temperature and flame stability? • Which options describe a direct and immediate result of extra unwanted air mixing with hot combustion gases, rather than a longer‑term side effect?

✅ Before You Answer

• Verify that inner casing air leaks introduce cool air into the gas side of the boiler, not into the water/steam circuit. • Check which choice is most closely tied to a drop in furnace or gas‑side temperature rather than changes in water usage or metal damage as a secondary effect. • Eliminate any options that would more likely result from poor circulation, scale, or flame impingement rather than from extra air entering the gas path.