PJF Gas Certification Practice Test

Introducing dilution air into a draft diverter of a natural draft furnace generally decreases the dew point temperature of the combustion products. This occurs because dilution air, which is typically cooler and contains more oxygen, mixes with the combustion gases. As this cooler air enters the system, it lowers the overall temperature of the combustion products.

The dew point is the temperature at which water vapor condenses into liquid form. By reducing the temperature of the combustion gases through dilution, the dew point also decreases. If the gases remain above the new, lower dew point temperature after dilution, condensation will be reduced. This is crucial for preventing corrosion in the flue and improving overall efficiency by ensuring that combustion gases exit the system without excess moisture.

In this context, while other options may suggest effects like no change or variability, the scientific understanding of how cooler air interacts with combustion gases aligns clearly with a decrease in the dew point temperature. This relationship is essential in maintaining the efficiency and longevity of the furnace system.