Radon is a naturally occurring radioactive gas that seeps into homes from the ground beneath them. It’s colorless, odorless, and tasteless, which means you can’t tell it’s there without a test. In the United States alone, radon is responsible for roughly 21,000 lung cancer deaths every year, making it the second leading cause of lung cancer after smoking.
Where Radon Comes From
Uranium is a naturally occurring element found in most soils and rock formations. As uranium slowly decays over time, it produces radium, which in turn decays into radon gas. Because radon is a noble gas, it doesn’t bond with other elements. It simply drifts upward through soil and into the air.
Outdoors, radon disperses harmlessly into the atmosphere. The problem starts when it seeps through cracks in a home’s foundation, gaps around pipes, sump pits, or exposed soil in crawl spaces. Once inside, radon gets trapped and accumulates to concentrations far higher than what you’d find outside. Any home can have elevated radon regardless of age, construction type, or geographic location, though certain regions with higher uranium content in the soil tend to produce more of it.
Why Radon Is Dangerous
When you breathe in radon, the gas itself passes through your lungs relatively quickly. The real danger comes from its decay products, tiny radioactive particles that can lodge in lung tissue. Over years of exposure, these particles damage cells in ways that can lead to lung cancer. The World Health Organization estimates radon causes up to 15% of lung cancers worldwide.
The risk climbs dramatically if you smoke. The lifetime risk of radon-induced lung cancer is about 62 per 1,000 for people who have smoked, compared to 7 per 1,000 for people who have never smoked. That’s nearly a tenfold difference. The combination of tobacco smoke and radon exposure is far more dangerous than either one alone.
There is no known safe level of radon exposure. Risk increases with both the concentration in your home and the number of years you spend breathing it in.
How Radon Levels Are Measured
Since your senses can’t detect radon at all, testing is the only way to know if your home has a problem. You can pick up short-term test kits at most hardware stores for under $20. These typically sit in the lowest lived-in level of your home for two to seven days and then get mailed to a lab for analysis. Long-term test kits, which measure for 90 days or more, give a more accurate picture of your average exposure since radon levels fluctuate throughout the day and across seasons.
Standard Geiger counters aren’t well suited for measuring radon because they pick up radiation from many sources, not just radon and its decay products. Purpose-built radon detectors, including continuous digital monitors, are much more reliable for this specific measurement.
What Radon Level Is Too High
The EPA recommends taking action if your home tests at or above 4 pCi/L (picocuries per liter). Because no level of radon is considered safe, the EPA also suggests considering mitigation for homes between 2 and 4 pCi/L. For context, the average outdoor radon concentration is about 0.4 pCi/L, so a reading of 4 pCi/L means indoor air roughly ten times more radioactive than what you’d find outside.
International standards vary. The International Atomic Energy Agency sets a maximum reference level of 300 Bq/m3 for homes, which is equivalent to about 8 pCi/L, a more lenient threshold than the EPA’s.
Seasonal Fluctuations in Radon
For most of the 20th century, radon levels were consistently highest during winter heating months. The logic was straightforward: homes are sealed up tight against the cold, so there’s less fresh air diluting indoor radon. Forced-air heating systems also pull air from basements and ground-level spaces and circulate it throughout the house.
That pattern has shifted. A growing number of North American homes now show higher radon in summer, likely because widespread air conditioning keeps houses sealed during warm months too. A Canadian study of paired winter and summer radon tests found that nearly half of buildings showed minimal seasonal difference. Among the rest, about 25% had meaningfully higher radon in winter, while 28% actually had higher levels in summer. The takeaway is that radon isn’t just a winter problem. Testing during any season can reveal an issue.
How Radon Mitigation Works
If your home tests high, the most common fix is called active soil depressurization. A licensed radon professional installs a PVC pipe that runs from beneath your foundation to above your roofline. A fan mounted in an unconditioned space (typically the attic, garage, or on an exterior wall) runs continuously, pulling radon-laden air from the soil before it can enter your home and venting it safely above the roof. The exhaust pipe must end at least 10 feet above ground and 10 feet from any windows, doors, or openings.
The specific approach depends on your home’s construction:
- Sub-slab suction pulls radon from directly beneath a concrete foundation through a suction pit dug below the basement floor.
- Drain tile suction taps into existing drainage pipes around the foundation and vents the soil gas outside.
- Sub-membrane systems are used in crawl spaces, where a sealed plastic sheet covers exposed dirt and a pipe draws soil gas from underneath it.
In all cases, cracks and openings in the foundation are sealed to limit radon entry points and help the system work more efficiently. A small U-tube gauge installed on the pipe gives you a quick visual check that the fan is maintaining suction. Some systems also include an active monitor that sounds an alarm if the fan stops working.
What to Expect From a Mitigation System
Professional installation typically takes a day and costs between $800 and $2,500 depending on your home’s layout and foundation type. Most systems reduce radon levels by 80% to 99%, often bringing a home from well above 4 pCi/L to below 2 pCi/L. The fan uses about as much electricity as a standard light bulb left on continuously.
After installation, you should retest your home to confirm the system is working. The EPA recommends retesting every two years or after any major renovation that could alter airflow patterns in your home. The fan will eventually need replacement (most last 5 to 10 years), and the U-tube gauge or alarm monitor makes it easy to notice when it’s time.