Which is NOT a recommended method for reducing radon levels in a home?

Keeping windows closed during summer is not a recommended method for reducing radon levels in a home because it does not actively mitigate the radon that may be present. In fact, closing windows can lead to increased indoor radon concentration by limiting airflow and ventilation, which helps to dilute indoor pollutants, including radon.

Effective radon reduction strategies typically involve measures that directly address the source or encourage ventilation. For instance, installing a radon mitigation system is a proven method that actively reduces radon entry. Sealing sump pumps and drains also helps to prevent radon gas from entering through these openings. Additionally, using high-efficiency air filters can improve indoor air quality, although they are not specifically designed to eliminate radon.

In contrast, simply keeping windows closed doesn't facilitate the necessary air exchange to reduce potential radon indoor levels, making it an ineffective approach to radon mitigation.