What is a potential cause of excessive soot accumulation in the heat exchanger of an LP gas furnace that was converted from natural gas?

Excessive soot accumulation in the heat exchanger of an LP gas furnace that was converted from natural gas is primarily caused by issues related to the fuel-to-air ratio. When a natural gas appliance is converted to operate on LP gas, the orifice size must be adjusted to accommodate the different energy content and combustion characteristics of LP gas. If the orifice (spud) is too large, it allows an excessive amount of gas to flow into the combustion chamber without a corresponding increase in air, resulting in an overly rich fuel mixture. This rich mixture leads to incomplete combustion, which produces soot as a byproduct.

Understanding this phenomenon is crucial, as it highlights the importance of proper conversion procedures for gas appliances, ensuring that the orifice size is calibrated correctly to maintain efficient combustion and prevent soot buildup. Proper maintenance practices and adherence to manufacturer guidelines play a significant role in the safe and efficient operation of heating appliances.