Where should you test for CO in an 80+ efficiency induced draft furnace?

Testing for carbon monoxide (CO) in an 80+ efficiency induced draft furnace is important to ensure safe operation and compliance with safety standards. The correct option focuses on an important aspect of furnace operation.

Testing in the vent above the inducer fan is ideal because it allows for accurate measurements of CO levels before the gases exit the vent termination into the atmosphere. This location is significant because it captures the emissions directly from the combustion process, helping to determine whether the furnace is operating within safe carbon monoxide levels.

Analyzing CO at this point provides insight into the efficiency of the exhaust system and the combustion process itself. High levels of CO found in this area might indicate issues like incomplete combustion, blockages in the vent system, or problems with the inducer fan's performance, which could trap dangerous gases within the living space if not diagnosed and repaired.

Testing at other locations, such as the vent termination or combustion chamber, may not give a complete picture of the CO levels relative to what is being expelled from the furnace into the environment. Testing in the living space can also pose safety risks and doesn’t provide accurate information about the furnace's condition. So, focusing on the vent above the inducer fan balances safety and effectiveness when monitoring carbon monoxide levels.