What is a common cause of white and yellowish deposits below the draft inducer fan of a furnace?

The presence of white and yellowish deposits below the draft inducer fan of a furnace is commonly associated with moisture condensing in the vent. When the combustion gases produced by the furnace cool, moisture can condense out of the gas and combine with other contaminants, leading to the formation of these deposits. This often occurs in systems where there is inadequate venting, leading to cool air mixing with the hot exhaust and allowing moisture to form.

The condensation can create a corrosive environment that can damage components over time, hence highlighting the importance of ensuring proper ventilation and exhaust systems in furnace operations. Understanding the role of moisture in this context is critical for home inspectors, as it can indicate potential issues with the furnace's venting system or its efficiency.