What is one common reason for soot buildup in a gas furnace?

Soot buildup in a gas furnace is often attributed to improper combustion, which can result from several factors. One significant reason is the size of the orifice. When the orifice size is too large, it can lead to an excess flow of gas, causing the combustion process to become inefficient. Inadequate combustion generates soot because not all of the fuel is burned completely, leading to the formation of carbon particles that accumulate as soot.

This situation contrasts with other potential causes of soot buildup. Insufficient fuel pressure can lead to a rich fuel mixture, but it typically results in incomplete combustion, which may not always produce soot. Using the incorrect gas type can cause various combustion issues, but soot production is primarily associated with the efficiency of the burning process rather than the type of gas used. Improper venting mainly leads to issues with exhaust gases and could create backdrafts or inadequate removal of combustion by-products, but is less directly linked to soot formation compared to orifice size.

Therefore, an oversized orifice is a direct contributor to inefficient combustion and subsequently, soot buildup in a gas furnace.