What can complicate the implementation of a sub-slab depressurization system?

The presence of a forced air furnace with return ducts under the slab can significantly complicate the implementation of a sub-slab depressurization system. This complication arises because the existing return ducts can interfere with the pressure differential needed for the depressurization system to function effectively. If the return ducts allow the air pressure to equalize within the system, it undermines the ability of the depressurization system to effectively draw radon from beneath the slab and vent it outside. This interaction can lead to inefficiencies in the radon mitigation system and result in inadequate radon reduction.

In contrast, the other factors listed, such as having a basement, high moisture levels in the soil, or reliance on passive mitigation systems, present their challenges but do not have the same direct impact on the operational effectiveness of a depressurization system. While they may complicate the overall mitigation strategy, they do not inherently disrupt the mechanics of the sub-slab depressurization process as significantly as the presence of forced air furnace ducts does.