While there is no safe level of radon, the Environmental Protection Agency (EPA) states that anything above 4 picocuries per liter (pCi/L) should be reduced.
A passive sub-slab depressurization system is designed to achieve lower sub-slab air pressure relative to indoor air pressure by use of a vent pipe routed through the conditioned space of a building and connecting the sub-slab area with outdoor air. This system relies solely on natural pressure differentials of air currents to draw air from beneath the slab. The changes in air pressure causes the air to flow up through the vent. Passive systems can be installed during construction of a new home or building.
While passive systems are energy-efficient, they are generally not as effective in reducing high radon levels.
Radon levels below 4 pCi/L have been achieved in all types of buildings using this system, but indoor radon levels can never be predicted and sometimes do not stay the same due to weather, different property and environmental conditions, building design, construction practices, and variations in the operation of buildings.
An active sub-slab depressurization system is designed to achieve lower sub-slab air pressure relative to indoor air pressure by use of a fan-powered vent drawing air from beneath the slab. The radon vent fan connected to the suction pipes creates a negative pressure beneath the slab and can actively draw the radon gas from below the home and release it into the outdoor air.