True or False: Windows must remain open on all levels of the building, including non-tested areas, under closed-building conditions.

The statement is false because under closed-building conditions, windows must remain closed in order to accurately assess radon levels. Closed-building conditions are established to minimize external influences on indoor air quality and to ensure that radon measurements are representative of typical living conditions. This means that while conducting a radon test, all windows, doors, and other openings should remain closed for at least 12 hours prior to the testing and throughout the duration of the measurement period. This allows for a consistent and reliable evaluation of radon concentration in the environment being tested. Keeping windows open would introduce outside air, potentially affecting radon levels and leading to unreliable results. Additionally, the requirement applies to all levels of the building and includes non-tested areas, as the goal is to maintain a controlled environment throughout the entire structure.