What is the function of the stack switch on an oil-fired furnace?

The function of the stack switch on an oil-fired furnace is primarily to ensure that combustion is taking place effectively. This safety device is typically located in the flue or stack of the furnace and monitors the temperature of the exhaust gases. If the furnace is not operating correctly and there is insufficient airflow through the flue, the temperature will drop, causing the stack switch to open and cut off power to the burner. This prevents the risk of dangerous conditions, such as the buildup of unburned oil or gas, ultimately safeguarding the furnace and the building.

The stack switch plays a critical role in safety, as it ensures that the combustion process is happening as intended, allowing for proper venting of exhaust gases. It helps maintain safe operational conditions, contributing to the overall reliability of the heating system.