--- title: How Does a Radon Mitigation System Work? canonical: "https://radonmitigationyorkpa.net/radon-guide/how-does-a-radon-mitigation-system-work/" pubDate: "2026-10-01T00:00:00.000Z" updatedDate: "2026-10-03T00:18:00.000Z" author: Radon Mitigation York PA description: "A plain-English look at how a radon system pulls soil gas from under your slab and vents it above the roof, part by part, plus how to tell it works." --- # How Does a Radon Mitigation System Work? A [radon mitigation system](/services/radon-mitigation-system-installation/) works by creating suction under your home. A fan pulls on a sealed pipe set into the soil below your basement slab. That puts the soil at lower pressure than your house, so radon flows into the pipe instead of through the floor, and the fan pushes it out above your roofline. ## Why radon gets into your house in the first place Radon is a colorless, odorless radioactive gas. It forms as uranium breaks down in soil and rock. In York County, which sits in EPA Radon Zone 1, the soil under many homes has plenty of it. Radon gets inside because of air pressure. Your house is usually at slightly lower pressure than the soil around it, especially in winter. Warm air rises and leaks out through the attic and upper floors. Exhaust fans, dryers and furnaces pull air out too. To replace that air, the house draws in air from below, including soil gas from under the slab. That soil gas finds any opening it can: cracks in the floor, the gap where the floor meets the wall, sump pits, floor drains, pipe holes, and the joints in block or stone walls. A mitigation system flips this pressure balance so the soil gas has an easier path out than in. ## The parts of a radon system, and what each one does Most systems in York use the same five parts. ### The suction point The installer cores a hole, usually 4 to 5 inches across, through the basement slab. Then they dig out a small pit of soil and gravel under it. This pit gives the fan a wide area to pull from. The pipe goes into the hole and the gap around it is sealed tight. ### The vent pipe PVC pipe, usually 3 or 4 inches across, runs from the suction point up and out of the house. It can run up the outside wall or up through a closet, garage and attic. Pennsylvania standards require the pipe to end at least 12 inches above the roof and 10 feet or more above the ground. It also has to be at least 10 feet from windows, doors and other openings, unless it is 2 feet above the top of them. ### The fan The fan is the engine of the system. It is an inline fan built for nonstop use, and it runs 24 hours a day. In Pennsylvania the fan cannot go in a basement, crawl space or living area. It must be outside the house or in an attic or garage that is not living space. That way, if the pipe ever leaked on the pushing side of the fan, radon would not be blown into your rooms. ### The manometer A small U-tube gauge on the pipe shows whether the fan is creating suction. The liquid sits higher on one side when the system is working. Pennsylvania requires every active system to have a way to check fan performance that you can see and read easily. ### Sealing The installer seals the major openings in the slab, like large cracks and the sump pit. Sealing does not stop radon by itself. Its job is to keep the fan from pulling basement air instead of soil gas, so the suction reaches farther under the floor. ## What happens when the fan turns on When the fan starts, it pulls air out of the pit under the slab. Air from the gravel and soil around the pit rushes in to fill the gap. Within minutes, a zone of lower pressure spreads out under much of the floor. Now the pressure has flipped. Before, the soil was pushing gas up into the house. After, the house is at higher pressure than the soil below it. Any small leak in the floor now pulls a little house air down into the soil, not the other way around. The radon that would have come in is drawn into the pipe and carried above the roof, where it mixes with outdoor air and thins out fast. This method is called sub-slab depressurization. For a deeper look, read our guide, [sub-slab depressurization explained](/radon-guide/sub-slab-depressurization/). The EPA's [Consumer's Guide to Radon Reduction](https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf) lists it as reducing indoor radon by 50 to 99 percent. ## How installers make sure the suction reaches the whole slab Not every basement has the same soil under it. Clean gravel lets air move easily, so one suction point can cover a large floor. Tight clay or packed fill slows air down, so the suction does not spread as far. Before installing, a good installer runs a quick diagnostic. They drill a small hole in the slab away from the planned suction point and check for a pressure change when suction is applied. If the far corners of the slab are not getting enough suction, they may add a second suction point or choose a stronger fan. Homes with more than one foundation type need extra planning. A basement with a crawl space addition, for example, may need suction under the slab and under a plastic sheet laid over the crawl space soil, tied into the same fan. ## Other system types you may hear about Sub-slab depressurization is the most common, but there are a few variations. - **Sump pit suction.** If your basement has a sump pit tied to drain tile, the installer can seal the pit lid and use it as the suction point. - **Sub-membrane depressurization.** For dirt or gravel crawl spaces, a heavy plastic sheet is sealed over the soil and suction is drawn from under it. - **Block wall suction.** For hollow block walls, suction can be drawn from inside the hollow cores. - **Passive systems.** Some newer homes were built with a pipe but no fan. These rely on natural airflow and usually work much better once a fan is added. ## How you know it is working You get proof in two ways. First, the clearance test. EPA guidance says to run a post-mitigation test no sooner than 24 hours after the system starts, and within 30 days. This shows your new radon level. Second, the manometer. Glance at it now and then. If the liquid levels are uneven, the fan is pulling. If they are level, the fan has stopped and needs attention. The EPA also suggests retesting your home at least every two years, and after any big remodel, to make sure the level stays low. ## Key takeaways - A radon system reverses the pressure under your home so soil gas is pulled out, not drawn in. - The core parts are a suction point, PVC vent pipe, an inline fan, a manometer and sealing. - Pennsylvania standards control where the fan goes and where the pipe discharges. - Sub-slab depressurization can cut radon by 50 to 99 percent, according to the EPA. - A clearance test and the manometer tell you the system is doing its job. ## Frequently Asked Questions ### Does a radon system run all the time? Yes. The fan runs 24 hours a day. Radon keeps forming in the soil, so the suction has to stay on to keep it out. Turning the fan off lets levels climb back up. ### Does a radon system clean the air already in my house? Not directly. It stops new radon from coming in. Normal air exchange then flushes out what was already inside, so levels drop within a day or so of the fan starting. ### Will a radon system lower my humidity? It can a little in some basements, because it pulls some moist soil air out from under the slab. It is not a dehumidifier, though, and should not be counted on as one. ## Talk to a York installer Want to see how this would work in your home? Call [(717) 356-3035](tel:+17173563035) any time for a free written quote and a same-day callback.