Rysmirs 4 Inch IP67 Waterproof Radon Mitigation Fan Series for Indoor Outdoor Installation -2 speed option, 280CFM at 45dB and 188CFM at 32dB, which could balance the noise level with the air volume, increase the comfort - Inside centrifugal impeller, radon fan use German-made motors, the speed reaches to 2600RPM, Easily and quickly improve the air circulation to keep fresh air in your area. -Noiseless duct fan system: The radon mitigation fan use unique design of the shell and the backward centrifugal impeller motor, with inside silencer cotton to reduce the noise produced. -Durable and strong plastic housing (ABS+PC) with UV protection, extend the product service life up to 10 years. -Proprietary deigned backward inclined centrifugal impeller build high volume suction and strong air exhaustion, widely used for household, industrial, building use. -You can immediately feel how efficiently it moves air through the system. It creates a strong, steady vacuum without needing to run at maximum speed all the time. The static pressure performance listed on the product page (350/280 Pa) matches well with what you can feel in real use. The overall functionality is reliable and consistent. -The Radon Mitigation System is a quality, quiet, and reliable solution for homeowners looking to reduce radon exposure. Its adjustable airflow, durable construction, and indoor/outdoor flexibility make it an excellent choice for both replacement and new installations.