Where should CO measurements be taken when testing a gas-fired furnace?

Taking carbon monoxide (CO) measurements in the vent pipe leaving the furnace is crucial for assessing the safe and efficient operation of gas-fired furnaces. This is because the vent pipe is where the combustion gases, including CO, exit the furnace and enter the flue system. Measuring CO at this location allows for the evaluation of how much carbon monoxide is being produced during combustion and whether it is being properly vented outside.

If CO levels are elevated in the vent pipe, it can indicate incomplete combustion, which could result from issues such as improper air-to-fuel ratios, blockages, or malfunctioning components. This measurement is essential for ensuring that the system is not only operating efficiently but also safely, as it helps prevent potential health hazards associated with CO buildup in living spaces.

In contrast, measuring CO in other locations mentioned—such as the fuel tank, return air duct, or basement area—would not provide an accurate representation of the emissions from the furnace or establish whether the venting system is functioning properly. The focus on the vent pipe makes this choice the most relevant and effective for assessing furnace performance and safety.