In measuring flue gas CO in a power-vented appliance, where should you measure?

Measuring flue gas carbon monoxide (CO) at the exhaust port located outside of the combustion appliance zone (CAZ) is the most effective method for obtaining an accurate assessment of the appliance's emissions. This location ensures that the measurement reflects the true condition of the flue gases as they exit the appliance into the venting system.

When taking CO measurements at this point, you can evaluate how well the appliance is operating and its potential impact on indoor air quality and safety. The conditions at the exhaust port can reveal important information such as whether the appliance is producing excessive CO due to incomplete combustion or if the venting system is functioning properly.

Measuring CO at other locations, such as the furnace inlet, chimney base, or ductwork, may not provide an accurate picture of the flue gas emissions. These locations can be influenced by various factors, such as backdrafts, dilution from indoor air, or other combustion pollutants that may not accurately represent the specific emissions from the combustion process. Therefore, measuring at the exhaust port located outside of the CAZ allows for a clear assessment of the operational performance of the appliance and its safety implications.