What increases indoor radon concentrations when the furnace blower is operating?

When the furnace blower is operating, leaky return ducts located in soil-contacted zones can significantly elevate indoor radon concentrations. This occurs because such ducts can draw in air from adjacent soil that may be contaminated with radon gas, especially if the soil has a high radium content or if there are radon sources nearby, such as certain rock formations or building materials.

As the blower operates, it creates a negative pressure in the return duct system, which can lead to a suction effect that pulls air (and any radon it may carry) from the surrounding soil into the home. This is particularly problematic if the ductwork is leaky and the return ducts are in contact with soil, as they can facilitate the entry of radon-laden air directly into the home’s ventilation system.

In contrast, sealed basement windows, properly insulated ducts, and air filtration systems do not enhance radon concentrations in the same manner. Sealed windows would help prevent outside air, including radon, from entering, while properly insulated ducts minimize temperature variation and reduce the likelihood of air leaks. Air filtration systems, depending on their design and effectiveness, are generally not intended to address radon and may not have a significant impact on radon levels. Thus, the presence