Why is condensate from a condensing furnace typically acidic?

Condensate from a condensing furnace is typically acidic primarily because of the characteristics of the combustion process itself. During the combustion of natural gas, which primarily consists of methane, various byproducts are created. When methane is burned, it combines with oxygen to produce carbon dioxide and water. However, when the combustion occurs in a condensing furnace, the flue gases are cooled to the point where water vapor condenses into liquid water, forming condensate.

As this condensate forms, it can dissolve gases such as carbon dioxide, which can lead to the formation of carbonic acid due to the reaction with water. If there are any trace impurities in the gas, such as sulfur compounds, these can lead to the formation of additional acids, such as sulfurous acid. Therefore, the nature of the combustion process and the resultant chemical reactions is what primarily contributes to the acidity of the condensate.

Understanding this process is crucial for HVACR professionals because the acidic nature of the condensate can affect drainage systems and materials involved, necessitating the use of corrosion-resistant materials in the handling of condensate. This knowledge helps in maintaining systems effectively and ensuring longevity and proper functioning.