What defines a 'closed-building' condition in the context of radon testing?

A 'closed-building' condition for radon testing is defined by the requirement that all windows and doors remain closed for a specified period, typically around 12 hours prior to and during the test. This condition ensures that there is minimal outside air exchange, which could dilute the radon concentration and lead to inaccurate measurements. Maintaining a consistent internal environment allows for the most reliable data on the radon levels present in the building, reflecting true exposure risk.

The focus on keeping windows and doors closed is crucial because it prevents external air, which may have different radon levels, from interfering with the testing process. This standard is key for achieving valid results, as any external ventilation would substantially alter the indoor radon concentration.

Recent construction or operational heating systems being off are factors that may influence the building's overall air exchange rates but do not directly define the necessary 'closed' condition for radon measurement.