Radon mitigation works by changing the air-pressure relationship between your house and the soil beneath it. A certified system pulls soil gas out from under the slab before it can enter the home, and discharges it above the roofline where it dilutes to background. Here is exactly how that happens, step by step, in a York County home.
Houses sit on soil that constantly exhales radon. The warm air inside a home rises, which lowers the pressure at the basement floor and pulls soil gas in through every crack, joint and sump pit — the stack effect. Roughly 56% of York County basement tests come back at or above the EPA action level of 4.0 pCi/L, so in this county the question is usually not whether soil gas is entering, but how much.
A contractor drills a small test hole through the slab and measures sub-slab pressure and soil permeability. That single reading decides everything: where the suction point goes, how big the fan must be, and whether one point is enough. Loose gravel communicates suction across the whole slab and needs a small fan; clay-rich fill needs high suction and sometimes two suction points. This is why two quotes for the same house can differ, and why a contractor who skips the diagnostic is guessing.
The suction point is a 4–5 inch hole, usually in an unfinished corner of the basement, located away from the HVAC returns so conditioned air is not pulled through the system. Three or four inch PVC pipe runs from it either up through the house and out the roof, or up an exterior wall. Every pipe joint is sealed; the sump pit gets a gasketed lid; slab cracks and the floor-wall joint are sealed so the fan pulls soil gas, not house air.
An inline centrifugal fan runs continuously, creating negative pressure in the gravel bed under the slab. The fan is sized to the diagnostic result, carries a five-year manufacturer warranty, and draws about as much power as a light bulb. A U-tube manometer on the pipe shows the pressure difference at a glance: unequal legs mean the fan is pulling; equal legs mean it has failed or a pipe is blocked.
A system without a test is a fan on a pipe. The post-mitigation test — at least 24 hours after fan startup — confirms the result, and well-designed systems reduce radon by 80–99%. A home testing at 12 pCi/L typically drops to 0.5–2.0 pCi/L. Sealing cracks alone is not a substitute: it supports the system, it does not replace it.
A standard installation is a same-day job: diagnostic in the morning, suction point, piping, fan and sealing in the afternoon, manometer and startup check before the contractor leaves. Passive systems in newer homes — a standpipe already routed to the roof — convert to active in under an hour.
Suction point design, fan selection and PA DEP certification details.
The full system page →The method behind more than 99% of installed systems (PA DEP). A fan pulls soil gas from the gravel or fill beneath your slab through a sealed pipe and discharges it above the roofline, where it dilutes to background. The house becomes a negative-pressure zone relative to the soil, so radon stops entering.
Well-designed systems reduce radon by 80–99% (EPA). A home testing at 12 pCi/L typically drops to 0.5–2.0 pCi/L. The post-mitigation test — at least 24 hours after fan startup — is the proof, and DEP requires mitigators to recommend one.
Fan size follows the sub-slab material, not the house size. Loose gravel communicates well and needs a small fan; clay-rich or tightly packed fill needs high suction and sometimes two points. The diagnostic test hole decides.
Two routes: a DIY kit ($10–$30, hardware store or online lab, 2–7 day charcoal or 90+ day track-et device) or a professional test with a continuous radon monitor ($150–$300, hour-by-hour data, tamper-resistant, results the same day the device comes out). Keep the house closed for 12 hours before and during a short-term test.
The lowest lived-in level — usually the basement. Not the kitchen, bathroom, or near windows, doors, exterior walls or drafts. PA DEP test records show basements read highest, and EPA’s action guideline is compared against that lowest-level reading.