Radon Facts: What Homeowners Need to Know
Radon is one of the few home hazards you cannot see, smell, or taste, which is exactly why the facts about it matter. It is the second leading cause of lung cancer in the United States, and Colorado’s geology puts the Front Range squarely in elevated-risk territory. The radon facts below cut through the noise so homeowners understand the real risk and the simple steps that address it. This guide summarizes EPA and CDC guidance current as of 2026; it is informational only, not a medical diagnosis, and a certified professional should handle testing and any mitigation decisions for your home.
Part of our Radon Levels guide — start there for the full picture →
The essential radon facts at a glance
Radon is a naturally occurring radioactive gas formed by the breakdown of uranium in soil and rock. It is colorless, odorless, and tasteless. It seeps into homes through cracks in foundations, gaps around pipes, sump pits, and crawl spaces, and it can accumulate to dangerous concentrations indoors. The EPA sets the action level at 4 pCi/L, meaning homes testing at or above that figure should take steps to reduce it.
The health risk is well established. Long-term exposure damages lung tissue through radioactive decay, and the EPA attributes roughly 21,000 lung cancer deaths a year in the United States to radon. The danger is cumulative and tied to years of exposure, not a single afternoon. Smokers face a sharply higher combined risk because tobacco and radon damage compound each other.
The reassuring fact is that radon is measurable and fixable. A test costs little, and mitigation systems reliably bring levels down. Knowing the numbers is the whole battle. Homeowners new to the topic can start with our broader radon testing guide for Front Range homeowners.
Where radon comes from
The source is the ground itself. Uranium occurs naturally in rock and soil across much of Colorado, and as it decays it produces radon gas, which migrates upward through soil pores. When that gas reaches a building, the slightly lower air pressure inside, driven by heating and ventilation, draws it in through any opening below grade.
Common entry points include foundation cracks, construction joints, gaps around service pipes, unsealed sump pits, and dirt-floor crawl spaces. Because the cause is geological rather than a defect in the house, even new, well-built homes can have high radon. The details of how the gas forms and moves are covered in our guide to what causes radon gas.
Why Colorado’s Front Range is high-risk
The EPA divides the country into radon zones, and much of Colorado, including Front Range counties such as Denver, Jefferson, Boulder, Douglas, and El Paso, falls into the highest-risk Zone 1. The state’s uranium-bearing soils and elevation contribute to elevated indoor readings that frequently exceed the national average. The geology of the Front Range, where the plains meet the foothills, includes the kinds of granitic and sedimentary formations that produce more radon at the source than flatter, clay-heavy regions elsewhere in the country.
Colorado’s climate compounds the geology. Long, cold winters mean homes stay sealed and heated for months, and the resulting indoor-outdoor pressure difference draws soil gas inward over an extended season. A home that might test moderately in a milder climate can register higher in Colorado simply because it spends more of the year closed up and pulling air from the ground beneath it. This is one reason testing during the heating season is common practice in the state.
Colorado’s health department reports that a large share of tested homes come back above the 4 pCi/L action level. That does not mean every home is dangerous, but it does mean a Front Range homeowner cannot assume their house is fine without testing. Neighboring homes can have very different levels because radon depends on the specific soil, foundation, and ventilation of each structure.
How radon is tested
Testing is simple and inexpensive. Short-term test kits sit in the lowest lived-in level of the home for two to seven days and give a quick snapshot. Long-term kits measure for 90 days or more and better reflect average exposure across seasons. Both are available as DIY kits, and certified professionals offer continuous-monitor tests that produce results in days.
The EPA recommends testing every home, retesting every two years, and testing again after any major renovation or HVAC change. Winter readings tend to run higher because homes are sealed and pressurized, which is why Colorado tests are often run in colder months. If a short-term result is high, follow up with a second test before deciding on mitigation. Buyers should ask for a radon test during the inspection period, a point our radon exposure overview reinforces.
Radon facts about levels and units
Radon is measured in picocuries per liter of air, abbreviated pCi/L. The picocurie is a unit of radioactivity, so the number describes how much radioactive decay is happening in the air, not a simple concentration like parts per million. Outdoor air averages around 0.4 pCi/L, and the EPA estimates the national indoor average near 1.3 pCi/L. The 4 pCi/L action level sits well above both, which is why a reading at that level signals a meaningful indoor accumulation.
An important fact many homeowners miss is that there is no level of radon considered completely risk-free. The 4 pCi/L figure is an action threshold, the point at which the EPA strongly recommends fixing the home, not a bright line between safe and dangerous. The agency notes that homeowners may also wish to consider reducing levels between 2 and 4 pCi/L. Risk rises with concentration, so lower is always better, and a home that tests at 8 or 12 pCi/L carries proportionally more risk than one at the action level.
Readings also fluctuate. The same home can test differently between summer and winter, between a sealed-up week and a well-ventilated one, and between the basement and an upstairs bedroom. That variability is why a single short-term test is treated as a screening step rather than a final verdict, and why long-term testing gives a truer picture of the average exposure that actually drives health risk.
Common myths and misconceptions
Several persistent myths cloud how people think about radon, and clearing them up is part of getting the facts straight.
“My neighbor tested fine, so I’m fine”
Radon depends on the specific soil, foundation, and ventilation under each individual house. Two homes side by side can produce very different readings, so a neighbor’s low result tells you almost nothing about your own home. Only a test of your house answers the question.
“New homes don’t have radon”
Because radon comes from the soil rather than building materials, new construction is just as susceptible as older homes. In fact, tightly sealed, energy-efficient new homes can concentrate radon because less outside air dilutes it. Some new homes are built with passive radon-resistant features, but those should still be tested and may need an active fan added.
“Radon is only a basement problem”
While the lowest level usually reads highest, radon migrates upward and can reach living spaces on any floor. The EPA recommends testing the lowest lived-in level, but a home without a basement, built on a slab or over a crawl space, can still have elevated levels throughout.
What to do about high radon
When a confirmed test sits at or above 4 pCi/L, mitigation is the answer. The standard fix is active soil depressurization: a fan and a sealed vent pipe pull soil gas from under the foundation and discharge it above the roof before it can enter the home. A typical residential system reliably lowers levels well below the action level, often to 2 pCi/L or less.
Sealing cracks alone is not enough; it helps the system but rarely solves the problem by itself. Mitigation is a one-time investment that keeps working for years with only an occasional fan replacement. Because the gas is invisible, the only proof a system works is a post-installation radon test confirming the drop. Mitigation costs vary by home and design, but for most Front Range houses it is a manageable expense relative to the protection it provides over decades of occupancy.
Homeowners sometimes ask whether they can simply ventilate the problem away by opening windows. Increased ventilation does lower levels temporarily, but it is not a permanent or practical solution through Colorado winters, and levels rebound as soon as the house is sealed up again. A dedicated mitigation system addresses the entry of soil gas at its source rather than diluting it after the fact.
Radon and home buying on the Front Range
Radon shows up frequently in Colorado real-estate transactions, and the facts matter most when money is on the line. Many buyers include a radon test in their inspection contingency, and a result at or above the action level becomes a negotiating point. Sellers may agree to install a mitigation system, offer a credit, or reduce the price so the buyer can handle it after closing.
A useful fact for buyers is that a mitigation system is a selling point, not a stigma. A home with a properly installed and documented system, backed by a post-installation test showing low levels, can actually be more attractive than an untested home, because the unknown has been resolved. Sellers who test and mitigate proactively often smooth their sale rather than complicating it.
For buyers, the practical steps are simple: request a radon test during the inspection period, confirm any existing system has a current passing test, and treat the issue as fixable rather than a dealbreaker. A high reading is a number to address, not a reason to walk away from an otherwise sound home. Colorado’s high prevalence means buyers encounter radon routinely, and experienced agents treat it as a standard part of due diligence.
Long-term protection and retesting
Radon facts do not stop at the first test. Because levels can change over time, with the seasons, after renovations, or as a foundation settles and develops new cracks, the EPA recommends retesting every two years and after any significant change to the home or its HVAC system. A home that tested low a decade ago is not guaranteed to test low today.
For homes with a mitigation system, retesting confirms the fan is still doing its job. Fans wear out, and a failed fan is silent, so the manometer gauge on the vent pipe and a periodic radon test together verify ongoing protection. Replacing a worn fan every several years is a minor cost that keeps the system effective.
Homeowners can also reduce risk through good practices that complement testing: sealing obvious foundation cracks, keeping sump pits covered, and maintaining balanced ventilation. None of these replace a mitigation system where one is needed, but they support a healthy indoor environment and can help keep borderline homes below the action level.
When to call a professional
A DIY test kit is a fine first step, but interpreting borderline results, diagnosing entry points, and designing a mitigation system call for a certified radon professional. State-certified or nationally certified mitigators understand local geology and code, and they verify their work with a follow-up test. A poorly designed system can leave levels elevated even when it appears installed.
Homeowners should call a professional after any confirmed reading at or above the action level, before buying a home in a high-radon zone, or when an existing system’s gauge shows it may have failed. The cost is modest against the long-term lung cancer risk that chronic exposure carries.
A certified mitigator also brings diagnostic tools a homeowner does not have. They can perform sub-slab communication testing to learn how easily air moves under the foundation, which determines where to place the suction point and how powerful a fan the home needs. They understand local code, proper discharge placement, and how to seal entry points so the system performs efficiently. That expertise is the difference between a system that quietly underperforms and one that reliably holds levels well below the action level for years. When the stakes are a known carcinogen accumulating in the air a family breathes daily, the certified route is the prudent one, and it is far less expensive than most homeowners expect.
References
- Health Risk of Radon — U.S. Environmental Protection Agency
- About Radon — Centers for Disease Control and Prevention
- Colorado Radon Program — Colorado Department of Public Health and Environment
Frequently asked questions
What is the most important radon fact for homeowners?
Radon is invisible and odorless but is the second leading cause of lung cancer in the U.S. The only way to know your level is to test. The EPA recommends taking action at or above 4 pCi/L.
Is radon a bigger problem in Colorado?
Yes. Much of the Front Range sits in the EPA's highest-risk Zone 1 because of uranium-bearing soils. A large share of tested Colorado homes come back above the 4 pCi/L action level, so testing is strongly advised.
How dangerous is radon really?
The EPA attributes about 21,000 lung cancer deaths a year to radon. The risk is cumulative over years of exposure and is much higher for smokers. A single short exposure is not the concern; chronic exposure is.
Can high radon be fixed?
Yes. A standard mitigation system uses a fan and vent pipe to draw soil gas from under the foundation and discharge it above the roof. It reliably lowers levels below the action level, confirmed by a follow-up test.
If you live on the Front Range and want a vetted professional to test your home or check an existing system, reach out through our contact page for a connection to a qualified local radon specialist.
Test your home for radon
Radon is invisible and odorless, so a test is the only way to know your level. A short-term kit gives a first reading in days; a digital monitor tracks it over time.
| Product | Why | Buy |
|---|---|---|
 AirChek Charcoal Radon Test Kit | Lab fee usually included; EPA short-term protocol. | Amazon — $21.95 |
 First Alert RD1 Radon Test Kit | Widely stocked; 48-hour charcoal test. | Amazon — $17.95 |
 Airthings Corentium Home | Digital monitor with a long-term average. | Amazon — $142.49 |