A radon mitigation system is a specialized setup designed to lower the concentration of radon gas inside buildings. Its primary goal is to protect occupants from the health risks associated with prolonged exposure to this naturally occurring radioactive gas. These systems operate by actively managing the movement of radon, preventing it from accumulating indoors to unsafe levels.
The Principle Behind Radon Mitigation
Radon mitigation systems operate by creating a pressure differential beneath a home’s foundation. This establishes a slightly lower pressure zone under the building compared to indoor air pressure. The system draws gas from the soil at its source, redirecting its natural path of entry into the home. This process captures and safely expels radon, which typically seeps through cracks and openings in the foundation.
Key Components of a Radon System
An active radon mitigation system comprises several interconnected parts. Collection pipes, usually made of PVC, gather radon gas from beneath the foundation. These pipes connect to a powerful radon fan, the system’s driving force. The fan is strategically placed in an unconditioned space, such as an attic, garage, or outside, to prevent any potential leakage of radon back into the home.
From the fan, an exhaust pipe extends vertically, directing the collected radon safely outdoors. This pipe must terminate above the roofline, typically at least 10 feet above ground and 10 feet away from windows or other openings, to allow for proper dispersion of the gas into the atmosphere. Additionally, sealing materials are extensively used to close cracks, gaps, and other potential entry points in the foundation. These sealants help maintain the necessary pressure differential for the system’s optimal function.
How Sub-Slab Depressurization Works
Sub-slab depressurization is the most widely used method for reducing indoor radon levels. This process begins with creating suction points by drilling a hole through the concrete slab into the soil or crushed rock beneath. A suction pit, often about one cubic foot in size, is excavated below this hole to enhance airflow and reduce resistance to the vacuum created by the fan. PVC collection pipes are then inserted into these suction points, extending through the slab.
The radon fan, connected to these pipes, continuously draws soil gas, including radon, from directly beneath the foundation. This active suction creates a negative pressure field under the slab, making its air pressure lower than inside the building. This pressure difference reverses the natural flow of radon, pulling it away from the building’s interior. The fan then expels the collected radon gas through the exhaust pipe, typically above the roofline.
Sealing any cracks, openings, or penetrations in the foundation, such as around utility pipes or sump pump covers, is an important step to ensure the system’s efficiency. This sealing helps maintain the negative pressure zone, ensuring the fan primarily draws from soil gas rather than conditioned indoor air, making the system more effective.
System Monitoring and Verification
Regular monitoring and periodic verification ensure a radon mitigation system’s continuous effectiveness. Most active radon systems include a U-tube manometer, a pressure gauge installed on the system piping. This U-shaped tube contains a colored liquid; uneven liquid levels indicate the fan is operating and creating the necessary suction. If the liquid levels are equal, it suggests the fan may not be working or there is a blockage within the system.
Beyond visual checks of the manometer, post-mitigation radon testing confirms that the system has reduced radon levels. The U.S. Environmental Protection Agency (EPA) recommends retesting every two years or after any significant structural changes to the home. These tests, often conducted using charcoal test kits or continuous radon monitors, provide quantitative data to verify that radon concentrations remain below the recommended action level, typically 4.0 pCi/L.