A radon mitigation system is not a filter. It is a pressure-management system: it changes the pressure relationship between the soil beneath your home and the air inside it, so soil gas moves away from the living space instead of into it. Understanding the main parts helps you read an installation proposal, ask better questions, and confirm that the finished work behaves the way it should. This page explains the common components and how they fit together. It is general education, not installation guidance — system design belongs to a qualified professional.

Why the soil is the starting point

Radon comes from the natural radioactive breakdown of uranium in soil, rock, and water, and it enters the air you breathe; inhaled radioactive particles can cause lung cancer, according to the EPA's radon resource directory. CDPHE describes how the gas "easily enters homes and other buildings through small openings like cracks in foundations, openings around pumps and drains, and crawl spaces" (2026 press release).

That list matters because it explains the design logic. Cracks and openings are not the problem to be sealed one by one — there are too many, and they change. The problem is the pressure differential that pulls soil gas through them. A mitigation system addresses the source side of that equation.

The two core approaches

CDPHE states that mitigation systems are the best way to reduce elevated radon levels, typically by preventing radon from entering the building, and that they can also dilute indoor air with outdoor fresh air (Testing and mitigating your home for radon). In practice, most residential work centers on one of two depressurization designs.

Sub-slab depressurization

For homes with a slab-on-grade or basement floor, CDPHE identifies sub-slab depressurization as usually the most effective solution. The idea: a collection point beneath the slab draws soil gas into a pipe rather than into the house, and a fan moves that gas outdoors above the roofline.

Sub-membrane depressurization

For homes with a crawl space, CDPHE names sub-membrane depressurization. A membrane covers the exposed soil, and the space beneath it is depressurized and vented the same way. The goal is identical; the collection surface is different.

The parts you will actually see

A typical system includes several visible elements. Their presence is not a performance guarantee, but they are the things you can inspect and ask about.

Suction point and piping

This is where the system meets the soil — through the slab or beneath the membrane — and the riser pipe that carries gas upward. Pipe routing, slope, and support are design decisions; the goal is a continuous, sealed pathway from the collection zone to the fan and out.

The fan

The fan creates and maintains the pressure difference. It is the only powered component in most systems, which is why its location, noise, and serviceability are worth discussing before installation rather than after.

Discharge above the roof

Gas is vented outdoors, terminating above the roof so it disperses rather than re-entering the home. The termination point is one of the easiest details to confirm on a final walkthrough.

The system indicator

A pressure gauge or similar indicator shows whether the fan is producing the intended pressure field. This is your routine check: a glance tells you the system is still operating, not whether indoor levels are acceptable. Only a test answers that.

Sealing and caulking

CDPHE is precise here, and the distinction is easy to get wrong. Caulking and sealing are done as part of mitigation, but the purpose "isn't to keep radon out but to hold conditioned air in." CDPHE notes it is impossible to seal all cracks, the task is time-consuming, expensive, and temporary, and sealing is "not recommended as a stand-alone technique." If someone offers to fix your home with sealant alone, that does not match state guidance.

A worked hypothetical

Consider a hypothetical Denver-area ranch home with a finished basement. A short-term test places a result at 6 pCi/L — above the EPA action level of 4 pCi/L, at which the EPA recommends fixing the home (EPA, January 2025). The homeowner hires a licensed mitigation professional.

In this hypothetical, the proposal specifies sub-slab depressurization, because the home has a slab. The installer cores a suction point in the basement slab, routes pipe to an exterior wall, mounts a fan outside the living space, and discharges above the roof. Cracks and penetrations are sealed to limit conditioned-air loss. A pressure indicator is installed where the homeowner can see it. None of this is a performance claim; it is a description of how the parts relate.

After installation, the homeowner does not rely on the gauge to confirm results. CDPHE guidance for homes with mitigation systems is to retest every two years to make sure the system is working properly. EPA guidance goes further in scope: every home tested at least every five years, or at least every two years to verify continued effectiveness of mitigation systems. A post-installation test establishes the starting point; the retest cadence confirms it holds.

What the equipment can and cannot promise

EPA Region 7 states that radon reduction systems can reduce a home's radon levels by up to 99% (January 2026). That figure is an upper bound, not a forecast for a particular house. EPA also notes that because there is no known safe level of exposure, Americans should consider fixing homes at levels between 2 and 4 pCi/L. System performance depends on soil, foundation type, and design — which is why the only meaningful check is a test of your home.

Cost context, for planning only: CDPHE describes a typical Colorado mitigation system as costing about $1,000–$2,000 unless difficult design problems are encountered. Treat that as historical context to verify, not a quote. CDPHE also operates a Low-Income Radon Mitigation Assistance program for qualifying homeowners; eligibility should be confirmed directly with CDPHE.

If your water comes from a private well

CDPHE advises that if your water comes from a private well and you found a radon problem by testing your home's air, you should also test the water. That is a separate system and a separate set of questions.

Your next step

Before signing anything, ask for a written design description: which depressurization approach, where the suction point goes, where the fan and discharge terminate, and how post-installation testing will be handled. Then compare what was proposed against what was built, and schedule the retest. Our questions to ask a radon professional page turns this into a checklist, and next steps covers how to read results against official guidance.