True or False: Testing should always occur with external fans operating.

Testing for radon levels should not occur with external fans operating because such fans can influence the air pressure in the home, leading to an inaccurate representation of radon levels. When external fans are running, they may create negative pressure and pull in outside air, which can dilute the indoor radon concentration and yield a lower reading than what is actually present in the absence of external airflow. Accurate testing should ideally reflect the natural radon levels in the home under normal living conditions, which means windows and doors should remain closed and mechanical ventilation devices like fans should be turned off.

Other scenarios, like testing only in hot weather or during long tests, do not address the critical impact that external air movement has on radon measurement. Therefore, the recommendation is always to conduct radon testing when external fans are not influencing the indoor air environment.