During a radon test, what should be the outdoor ventilation rate for an energy recovery or heat recovery ventilator?

The correct choice indicates that the lowest outdoor ventilation rate for the season is appropriate during a radon test when using an energy recovery or heat recovery ventilator. This is important because ensuring adequate but not excessive ventilation helps maintain external radon levels in a range that can inform indoor measurements. By using the lowest outdoor ventilation rate, it minimizes the potential dilution of indoor radon concentrations while still allowing for some fresh air exchange, which can help in obtaining an accurate representation of radon levels within the building during testing.

Frequent changes in ventilation rates can lead to fluctuations in indoor air quality and radon concentration levels, potentially skewing test results. Therefore, using a controlled, lower ventilation rate during the test period aligns with best practices for radon testing—a method designed to assess the natural indoor radon levels without interference from external factors, such as enhanced ventilation that could dilute radon concentrations, causing misleadingly low test results.