Radon is a colorless, odorless, radioactive gas that seeps into homes from the ground. It’s the second leading cause of lung cancer in the United States — responsible for an estimated 21,000 deaths annually — and the leading cause among non-smokers. The EPA estimates that approximately 1 in 15 American homes has radon levels at or above the recommended action level of 4 pCi/L. You can’t see it, smell it, or taste it. The only way to know if your home has a radon problem is to test.
What Is Radon and Where Does It Come From?
Radon (Rn-222) is a naturally occurring radioactive gas produced by the decay of uranium, which is present in varying concentrations in soil and rock worldwide. As uranium breaks down through its decay chain, it produces radium, which then decays into radon gas. This gas migrates through soil and can enter buildings through any opening that contacts the ground.
How Radon Enters Your Home
Radon levels vary dramatically by geography. Areas with granite bedrock, shale, and phosphate-rich soils tend to have higher radon potential. However, elevated radon has been found in every state — even in areas considered “low risk.” The only reliable way to know your home’s radon level is to test it.
Health Risks: Radon and Lung Cancer
When you inhale radon, it decays inside your lungs, releasing alpha particles — a form of ionizing radiation. These alpha particles damage the DNA in lung cells, which can lead to lung cancer over years of exposure. The risk is cumulative: the higher the radon level and the longer the exposure, the greater the risk.
Risk by Radon Level
The EPA provides these lifetime risk estimates for lung cancer based on radon exposure:
| Radon Level (pCi/L) | Non-Smoker Risk | Smoker Risk | Comparable Risk |
|---|---|---|---|
| 20 pCi/L | 36 per 1,000 | 260 per 1,000 | 250x the risk of drowning |
| 10 pCi/L | 18 per 1,000 | 150 per 1,000 | Comparable to dying in a house fire |
| 8 pCi/L | 15 per 1,000 | 120 per 1,000 | 8x the risk of dying in a car crash |
| 4 pCi/L (EPA action level) | 7 per 1,000 | 62 per 1,000 | 5x the risk of dying in a car crash |
| 2 pCi/L | 4 per 1,000 | 32 per 1,000 | Comparable to risk of dying in a car crash |
| 1.3 pCi/L (avg outdoor) | 2 per 1,000 | 20 per 1,000 | Average outdoor exposure |
The interaction between radon and smoking is synergistic — the combined risk is much greater than either risk alone. A smoker living in a home with 4 pCi/L radon has a lung cancer risk of about 62 per 1,000 — nearly 9 times higher than a non-smoker at the same radon level.
There Is No “Safe” Level
The EPA is clear: there is no known safe level of radon exposure. Any radon exposure carries some risk. The 4 pCi/L action level is a practical threshold — not a safety guarantee — representing a balance between health protection and the feasibility of mitigation. The WHO recommends a lower action level of 2.7 pCi/L (100 Bq/m³). The EPA also recommends considering mitigation for levels between 2-4 pCi/L.
How to Test for Radon
Radon testing is simple, inexpensive, and the only way to know your home’s radon level. Every home should be tested, regardless of location, age, or construction type.
Short-Term Tests (2-7 Days)
Short-term test kits are the quickest way to get an initial reading. They use charcoal canisters or alpha track detectors that you place in the lowest livable level of your home (usually the basement or ground floor) for 2-7 days, then mail to a laboratory for analysis.
Long-Term Tests (90+ Days)
Long-term tests provide a more accurate picture of your home’s average radon level over time, accounting for seasonal and weather-related fluctuations. Alpha track detectors and electret ion chambers are common long-term test devices.
Continuous Radon Monitors
Electronic radon monitors provide real-time, continuous readings. Consumer models like the Airthings Wave Plus, Ecosense RadonEye, and Corentium Home display current radon levels and track trends over time.
Professional Testing
Certified radon measurement professionals use calibrated equipment and follow standardized protocols. Professional testing is recommended for real estate transactions and when you need legally defensible results.
Testing Best Practices
Radon Mitigation: How to Reduce Levels
If testing reveals radon levels at or above 4 pCi/L (or between 2-4 pCi/L if you want extra protection), mitigation can reduce levels by up to 99%. The most common and effective method is Active Soil Depressurization (ASD).
Active Soil Depressurization (ASD)
ASD is the gold standard for radon mitigation. A pipe is inserted through the foundation slab into the soil beneath the house. A continuously running fan creates negative pressure under the slab, drawing radon-laden soil gas from beneath the house and venting it above the roofline where it disperses harmlessly into the atmosphere.
Other Mitigation Approaches
Can Air Purifiers Remove Radon?
No. This is a critical point: air purifiers — including HEPA and activated carbon filters — do not effectively remove radon gas from indoor air. Radon is a noble gas (chemically inert) that passes through all consumer-grade filters without being captured. Some air purifiers can capture radon decay products (the radioactive particles produced when radon decays), which provides a small reduction in radiation exposure, but this is not a substitute for proper mitigation.
If your home has elevated radon, the only effective solution is a radon mitigation system (typically ASD) that prevents radon from entering the living space in the first place. Don’t rely on air purifiers, ventilation, or sealing alone.
Radon in Water
Radon can dissolve in groundwater and enter homes through the water supply, particularly in homes with private wells. When radon-contaminated water is used for showering, washing, or cooking, the radon is released into the air. The EPA estimates that radon in water causes about 168 cancer deaths per year in the US — far fewer than airborne radon, but still a concern.
Frequently Asked Questions
Q: Does every home need to be tested for radon?
Yes. The EPA recommends testing every home below the third floor, regardless of geographic location. Radon levels can vary dramatically between neighboring houses — your neighbor’s low reading doesn’t guarantee yours is low. Testing is inexpensive ($10-30 for a DIY kit) and takes minimal effort.
Q: Can radon levels change over time?
Yes. Radon levels fluctuate daily, seasonally, and over years due to changes in soil moisture, barometric pressure, wind, snow cover, and home ventilation patterns. Levels are typically highest in winter (when homes are sealed tight) and lowest in summer (when windows are open). This is why long-term testing provides a more accurate picture than a single short-term test.
Q: Does a new home need radon testing?
Absolutely. New construction doesn’t guarantee low radon. While some new homes are built with radon-resistant features (passive radon systems), these features don’t eliminate radon — they make it easier to add active mitigation if needed. Test any new home before or shortly after moving in.
Q: How much does radon mitigation cost?
Professional ASD installation typically costs $800-2,500, with most homes falling in the $1,000-1,500 range. Ongoing electricity costs for the fan are $50-100/year. Fan replacement every 5-10 years costs $100-300. Compared to the health risk of long-term radon exposure, mitigation is a modest investment.
Q: Will radon mitigation affect my home’s resale value?
A properly installed and documented radon mitigation system is generally viewed positively by buyers — it demonstrates that the issue has been identified and addressed. In many markets, homes with mitigation systems sell without issue. Conversely, a home with known elevated radon and no mitigation can be a deal-breaker for informed buyers.
The Bottom Line
Radon is a serious, well-documented health risk that’s entirely manageable once you know about it. Test your home — it takes minutes to set up and costs less than a pizza. If levels are elevated, professional mitigation is effective, affordable, and typically completed in a single day. Don’t rely on air purifiers for radon — they can’t remove this gas. And if you smoke, reducing radon exposure is especially critical because the combined risk is dramatically higher than either factor alone.
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