Which symptom is associated with flooding in a furnace?

• A. Flame temperature decreases
• B. Flame temperature increases
• C. No change in temperature
• D. Flame becomes more stable

Answer: (A)

Flooding means there is too much fuel for the amount of air available for complete combustion. When the mixture is rich, oxidation cannot proceed efficiently, so not all fuel reacts and the flame front is cooled by the excess unburned fuel and by the incomplete reactions. The result is a lower flame temperature, since the energy from combustion isn’t released as fully or as quickly as with a properly balanced mix. That cooling effect is the main symptom you’d expect to see in a flooded furnace.

You might also notice signs of incomplete combustion, like smoke or soot, but the key temperature change you’d observe is a cooler flame. A hotter flame would come from too much energy release, which flooding does not provide, and a completely unchanged or more stable flame wouldn’t align with the disruption caused by a fuel-rich condition. To fix it, adjust toward a correct air-to-fuel ratio by increasing air or reducing fuel.