There are several types of Active radon reduction systems. When referring to radon reduction, Active generally means a fan is installed to control air pressures and direction of air movement. By far the most common types of active radon reduction systems are Sub-Membrane and Sub-Slab Depressurization or a combination of both, the EPA definitions of each are:
A radon control technique designed to achieve lower air pressure in the space under a soil gas retarder membrane laid on the crawl- space floor, relative to air pressure in the crawlspace, by use of a fan-powered vent drawing air from beneath the membrane.
Sub-Slab Depressurization (Active):
A radon control technique 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 concrete slab.
Arrows indicate the direction of air flow with Active Soil Depressurization.
The negative pressure field beneath the slab caused by the system has reversed the normal direction of soil gas flow into the house.
Radon and other soil gases are drawn indoors primarily by the lower air pressure in the house compared to that of the soil. To reduce radon-bearing soil gas from entering the house, a small fan (with associated piping) can be used to withdraw radon directly from the soil.