Comparison of natural and forced ventilation for radon mitigation in houses

Radon mitigation by natural basement ventilation was compared to mitigation by forced ventilation (pressurization) and to mitigation by the operation of a modified heating and air conditioning (HAC) system in a series of experiments conducted during the spring and summer in a research house. Both natural ventilation and basement pressurization reduced average basement radon concentrations from 800 Bq m^-3 to less than 150 Bq m^-3. Natural ventilation reduced radon levels both by dilution and by decreasing basement depressurization and thus the radon entry rate. Basement pressurization reduced radon levels by increasing ventilation and lowering subslab radon levels, but is significantly more difficult to implement than natural ventilation. The operation of the forced air HAC system with a duct that supplied additional outside air to the return side did not reduce indoor radon concentrations. These experiments have clearly demonstrated the relationship between the outdoor-basement pressure differential and the radon entry rate, ventilation rate, and radon levels.