In oil-burning appliance combustion products, the dew point is the temperature below which components condense on exposed surfaces.

• A. Condense
• B. Evaporate
• C. Oxidize
• D. Sublimate

Answer: (A)

Dew point is the temperature at which water vapor in a gas becomes saturated and begins to condense into liquid on surfaces. In oil-burning appliance exhaust, the hot combustion gases contain a lot of water vapor. As these gases travel through the vent or flue and cool, they reach the dew point. Below that temperature, the water vapor condenses on cooler surfaces, forming liquid condensate (which can become acidic if sulfur compounds are present). This is condensation—not evaporation, oxidation, or sublimation—so the correct idea is that condensation occurs at and below the dew point.