Remediation
How radon mitigation works
Radon gets into a building because the air inside is at slightly lower pressure than the soil beneath it, so the ground vents into the house through every crack, joint and pipe penetration in the slab. Mitigation works by reversing that pressure difference: it gives the soil gas an easier route to the outside than the route through your floor.
The standard technique
Active sub-slab depressurisation
The system that fixes the large majority of houses is a pipe through the slab into the aggregate beneath it, an inline fan, and an exhaust that discharges above the roofline. The fan holds the space under the slab at lower pressure than the room above it. Soil gas now takes the pipe instead of the floor.
Suction point
A hole cored through the slab, with material excavated beneath it to create a cavity the system can draw from. Large or subdivided slabs may need more than one.
Sealing
Cracks, the floor-wall joint, sump covers and pipe penetrations are sealed. Sealing alone rarely fixes a house, but it makes the fan far more effective.
Fan and riser
An inline fan, mounted outside the living space - in the attic, garage or outdoors, never in a basement, so a leak in the pipe cannot pressurise the house.
Exhaust
Discharged above the eave, away from windows, doors and air intakes, so what leaves does not come straight back in.
Other foundations
When the house is not on a slab
Crawlspace - sub-membrane depressurisation
A heavy plastic membrane is laid over the crawlspace floor and sealed to the walls and piers, and the fan draws from beneath it. Functionally the same system, with the membrane playing the part of the slab.
Drain tile or sump
Where the house has a perimeter drain or an interior sump, the system can often draw from it directly. A sump pit gets a sealed lid with a fitting for the suction pipe.
Block wall depressurisation
Hollow-block foundation walls are themselves a radon route. The cavity inside the wall can be depressurised, usually alongside a sub-slab system rather than instead of it.
Passive systems and new construction
A passive system uses the same pipework relying on the stack effect rather than a fan. It costs far less to build into a new house than to retrofit, and a fan can be added later if a test shows it is needed. Building codes in many high-radon jurisdictions now require radon-resistant construction.
Judging the work
What a good installation looks like
Signs of a good job
- A visible manometer on the riser, showing the system is drawing. It is the only way to tell at a glance that the fan is still working.
- A label stating the installer, the date and the system type.
- The fan mounted outside the conditioned space, never in the basement.
- Exhaust discharging above the roof eave and well clear of windows and intakes.
- A post-mitigation test, done at least 24 hours after the system starts, documenting what it achieved.
- A written guarantee of the level the system will reach.
Signs to walk away
- A quote given without anyone looking at the foundation.
- Sealing offered on its own as the fix.
- A fan installed inside the basement or crawlspace.
- Exhaust terminating at ground level or beside a window.
- No post-installation test offered.
- No certification through the NRPP or NRSB, and no state licence where the state requires one.
Cost ranges and system descriptions follow the EPA Consumer’s Guide to Radon Reduction. Installation practice follows the ANSI/AARST mitigation standards. Certification in the United States is through the National Radon Proficiency Program (NRPP) and the National Radon Safety Board (NRSB); many states license separately.
Equipment
Confirming the system keeps working
The failure mode of a mitigation system is silence: the fan stops, the manometer sits level, and nobody notices for a year. A continuous monitor is the cheap insurance against a house everyone believes is fixed.
Continuous radon monitors
Affiliate linksElectronic monitors that read continuously rather than once. Useful after mitigation, when a system's fan can fail silently.
Airthings
Airthings Corentium Home Radon Detector 223 Portable, Lightweight, Easy-to-Use, (3) AAA Battery Operated, USA Version, pCi/L
AEGTEST
AEGTEST HOUND-1011S Portable Radon Detector, High-Accuracy Sensor for Home, Lightweight, Audible & Visual Alarms, Long-Term Monitoring, Easy-to-Use Radon Tester in pCi/L or Bq/m³ for Basement
Airthings
Airthings 325 Corentium Home 2 Smart Digital Radon Detector - Portable and Easy-to-use Radon Testing with Bluetooth connectivity and Humidity & Temperature Sensors
AEGTEST
AEGTEST HOUND-1011S Portable Radon Detector, High-Accuracy Sensor for Home, Lightweight, Audible & Visual Alarms, Long-Term Monitoring, Easy-to-Use Radon Tester in pCi/L or Bq/m³ for Basement
Prices retrieved from Amazon on 2026-08-21 and may since have changed; the price on Amazon at the time of purchase is the one that applies. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. No manufacturer pays for a place in this list.
Questions
Common questions about mitigation
How much does radon mitigation cost?
The EPA puts a radon reduction system at roughly $800 to $2,500, with around $1,200 typical. The spread comes from foundation type, how far the exhaust has to run, whether the slab needs multiple suction points, and local labour rates. A house on a slab with easy access to an exterior wall sits at the low end; a house with a mixed foundation, a finished basement and a long interior riser sits at the high end.
How much does the system cost to run?
The fan runs continuously and typically uses about the same electricity as a 60 to 90 watt bulb, on the order of $75 to $175 a year, plus a modest heating and cooling penalty from the air the system removes. Fans generally last around 5 to 10 years and cost a few hundred dollars to replace.
How far will it bring the level down?
A well-designed sub-slab depressurisation system commonly reduces indoor radon by 80% or more, and bringing a home from well above the action level to below 2 pCi/L is a normal outcome. The EPA advises retesting after installation to confirm what the system actually achieved.
Can I install one myself?
It is physically possible and some homeowners do it, but sizing the fan, choosing suction points, sealing the slab and routing the exhaust so it does not re-enter the building are all things done badly by people doing them once. A poorly designed system can move radon around the house rather than out of it. Certified contractors are certified through the NRPP or the NRSB, and many states maintain their own licensing.
Does it need to be disclosed when I sell?
Rules vary by state, and many require disclosure of known radon results and of any mitigation system. A properly installed and documented system is generally an asset in a sale, because it answers the question a buyer's inspector would otherwise raise.
Before any of this
Test first
No house needs a mitigation system until a test says it does, and a county radon zone is not a test. Testing costs a small fraction of mitigation and is the step that decides everything after it.