Soil gas enters a house because the space under the floor is at a slightly higher pressure than the space above it, so gas moves upward through whatever openings exist. A mitigation system does not filter the air, scrub it or treat it. It changes which direction the gas wants to travel by making the space beneath the slab the lower-pressure destination, so soil gas moves into a pipe instead of into the living space.
That is genuinely the whole concept. Everything else is plumbing: where to take suction, how to route the pipe, how big a fan the conditions require and how to keep every joint sealed. Once you understand that the system is winning a small pressure contest under your floor, the parts stop looking like a mystery and start looking like an obvious solution to a specific problem.
The system starts with a hole cored through the slab and a small cavity excavated beneath it. That cavity is where the fan takes hold. How far its influence spreads depends on what is under the concrete: clean aggregate lets suction travel a long way, while tight soil or fill limits it sharply. This is why placement is a decision rather than a convenience, and why two houses that look alike from the street can need different numbers of suction points.
Good contractors do diagnostic work before committing. A communication test checks how far suction actually reaches from a candidate point, which answers whether one suction point covers the slab or whether the house needs more than one. Skipping that step is how a house ends up with a system that runs perfectly, looks correct, and does not bring the number down in the far corner of the floor.
From the suction point, sealed pipe carries soil gas up and out. The route is chosen for practical reasons: the shortest sensible path, somewhere the pipe can be concealed or at least be unobtrusive, and away from bedrooms where fan noise would be noticed. Interior routes through a utility chase are usually tidier than exterior routes, though a finished house sometimes leaves no interior option.
The fan is inline, mounted outside the living space, and sized to the conditions under the slab rather than picked off a shelf. It runs continuously and quietly. The pipe terminates above the roofline, positioned away from windows and air intakes so the discharge disperses rather than finding its way back inside. A small gauge on the pipe gives the homeowner a visible indication that suction is present.
Sealing supports the system rather than replacing it. Cracks, the joint where the foundation wall meets the floor, slab penetrations and open sump pits are the easy paths, and if they are left open the fan spends its energy pulling house air down and back out instead of pulling soil gas. A sealed sump lid with the right fittings is a common part of the work, and sometimes the sump or existing drain tile becomes the suction path itself.
Crawl spaces are handled differently because there is no slab to core. The usual approach is a sealed membrane laid over the crawl space floor, taped and fastened at the edges, with the system drawing from beneath it. A house with both a slab and a crawl space gets both treatments, sometimes tied into one pipe run and sometimes as separate suction points, depending on the layout.
Once it is running, the system asks very little of you. It is left on permanently, since switching it off returns the house to its previous behavior. The fan uses a modest amount of electricity. The one habit worth forming is glancing at the gauge on the pipe occasionally, because a stopped fan announces itself in no other way: no smell, no sound, no visible change indoors.
The rest is periodic. Fans have a service life and are replaced when they reach it, which is a small job that reuses the existing pipe run. Retest after any service work, after any change to the foundation or how the house handles air, and periodically regardless. Keep the installation paperwork, the post-installation test and any later results together, because a system with a documented history is worth more when the house sells.
No, and that is a useful thing to be clear about. A mitigation system intercepts soil gas beneath the slab and vents it above the roof before it enters. It is not an air purifier, it does not filter what is already circulating indoors, and it is not a substitute for ventilation. Its entire job is to change where the gas under your floor goes.
Barely, when it is installed well. The fan is mounted outside the living space and makes a low steady hum, and there is some air noise in the pipe. Routing is part of the design, and a fan placed beside a bedroom wall is the usual reason someone finds a system annoying. If a quiet system becomes noticeably louder over time, treat that as a service prompt.
The parts are not exotic, but the parts are not the hard portion. Diagnostics determine where suction should be taken and how many points a slab needs, fan sizing depends on what is under the concrete, and the discharge has to terminate correctly relative to the roofline, windows and intakes. Getting any of those wrong produces a system that runs without lowering anything, which a retest will reveal.
Radon is produced in soil and rock and moves naturally upward through the ground. A house sitting on that ground is, in air pressure terms, slightly hungry: warm air rises…
Read the guide →Testing as a homeowner is leisurely. You place a device, you keep the house closed, you read the result whenever it comes and you decide at your own pace. Testing during a…
Read the guide →Test first, then decide. There is no fee to be matched.
Arrange a TestCounty, foundation type, and whether a deadline is involved is enough to start.