What defines steady state conditions in CO concentration testing?

In CO concentration testing, steady state conditions are defined by the flue gas temperature leveling off after a specific period, typically after 5-10 minutes of operation. This leveling off indicates that the combustion appliance has reached a consistent operating condition where combustion gases are stable and representative of the typical performance of the appliance.

When the flue gas temperature stabilizes, it suggests that the combustion process has balanced out, and the combustion products, including carbon monoxide (CO), can be accurately measured. A consistent temperature indicates that the appliance is operating under a steady state, which is crucial for ensuring that the CO concentration readings reflect normal operation rather than transient states that might occur during startup or shutdown phases.

In contrast, other options suggest conditions that do not accurately reflect steady state. For instance, firing for a brief 1-3 minutes may not be sufficient for the appliance to stabilize, and an uninterrupted operation for 20 minutes may include fluctuations. Reaching maximum output temperature instantly disregards the natural buildup time of combustion processes, which is not consistent with how appliances operate under normal conditions. Thus, the emphasis on the flue gas temperature stabilizing is essential for ensuring valid and reliable CO concentration measurements.