In high efficiency furnaces, if the flue gas temperature drops below 65 degrees C, what happens?

In high-efficiency furnaces, if the flue gas temperature drops below 65 degrees Celsius, water vapor condenses. This occurs because as the flue gas cools, it reaches its dew point, which is the temperature at which water vapor within the gases can no longer remain in gaseous form and begins to condense into liquid water.

This condensation is a key feature of high-efficiency systems, as it allows the recovery of latent heat from the water vapor in the exhaust gases, improving overall energy efficiency. The condensed water can be drained away, which is essential for preventing corrosive damage to the furnace and flue system. Thus, the ability of the high-efficiency furnace to operate at lower temperatures and facilitate condensation is crucial for its high-performance standards and effective heat recovery.