What Is Radon?
Radon is a radioactive gas that forms naturally when uranium in soil, rock, and water breaks down. It's part of the natural environment, present everywhere in trace amounts. The problem occurs when radon gas seeps into enclosed spaces—like your home—and concentrates to dangerous levels.
Unlike carbon monoxide or natural gas leaks, radon is completely undetectable without specialized testing equipment. It has no odor, no color, and no taste. This is why the EPA and Surgeon General recommend that all homes be tested for radon, regardless of location.
Key Facts:
- •Radon-222 has a half-life of 3.8 days, meaning it continuously decays into other radioactive particles
- •These decay particles attach to dust and moisture in your lungs, delivering radiation directly to lung tissue
- •Long-term exposure—typically 20-30 years—dramatically increases lung cancer risk
How Radon Gets Into Your Home
Radon moves up through the ground and into your home through cracks and gaps in the foundation. Because indoor air pressure is usually lower than the soil pressure around the foundation, your house acts like a vacuum, drawing radon gas inside.
Common Entry Points:
- • Cracks in concrete floors and walls
- • Gaps around service pipes
- • Construction joints
- • Gaps in suspended floors
- • Cavities inside walls
- • Sump pump openings
- • Well water (released when water is used)
Factors That Increase Risk:
- • Uranium-rich soil and bedrock
- • Granite or shale geology
- • High soil permeability
- • Basement or crawl space foundation
- • Older homes with settling cracks
- • High indoor-outdoor pressure differential
- • Private well water (some areas)
Important: New homes are just as susceptible as old homes. Modern construction techniques create more airtight homes, which can actually trap and concentrate radon gas. New construction in high-risk zones should include radon-resistant features, but testing is still essential.
Radon Risk by Location: EPA Zone Map
The EPA divides the United States into three radon zones based on predicted average indoor radon levels. However, high radon levels have been found in homes across all 50 states. The only way to know your home's radon level is to test—zip code predictions aren't enough.
Zone 1 (High)
Predicted average indoor level: >4 pCi/L
Includes counties in Iowa, North Dakota, Pennsylvania, Colorado, and parts of 30+ other states
Zone 2 (Moderate)
Predicted average indoor level: 2-4 pCi/L
Mixed geology areas—some homes will exceed 4 pCi/L, others won't
Zone 3 (Low)
Predicted average indoor level: <2 pCi/L
Lower predicted averages, but high levels still possible—testing recommended
Why Geography Isn't Everything
Two identical homes on the same street can have vastly different radon levels. Variations in soil composition, foundation construction, ventilation, and even weather patterns affect indoor radon concentrations. The EPA zone map is a starting point for policy—not a substitute for testing your specific home.
Check Your City's Radon Risk Level
We've compiled EPA radon zone data and local testing statistics for 50+ major US cities. See what radon levels are typical in your area:
Health Risks: Why Radon Is Dangerous
The Statistics Are Sobering:
- • 21,000 lung cancer deaths per year in the US from radon exposure
- • 2,900 deaths among non-smokers—radon is the #1 cause of lung cancer in people who never smoked
- • Smokers exposed to radon have 10x higher lung cancer risk than non-smokers exposed to radon
- • Risk increases with exposure time and radon concentration
When you breathe air containing radon, radioactive particles enter your lungs. These particles decay and release bursts of radiation that damage lung tissue. Over time—typically 20-30 years of exposure— this damage can lead to lung cancer.
There is no "safe" level of radon exposure. The EPA action level of 4 pCi/L is a guideline for when mitigation is recommended, but health risks exist at lower levels too. Some experts argue that any level above 2.7 pCi/L (the average outdoor level) poses unnecessary risk.
Who Is Most at Risk?
Children
Higher breathing rates and developing lungs make children more vulnerable to radiation damage
Smokers and Former Smokers
Combined exposure to radon and tobacco smoke multiplies lung cancer risk exponentially
People Who Spend Time in Basements
Radon concentrations are typically highest in basements and ground-floor rooms
Long-Term Residents
Lung cancer risk from radon is cumulative—decades of exposure in the same home increases risk
How to Test for Radon
Testing is the only way to know if you have a radon problem. The EPA and Surgeon General recommend testing all homes below the third floor. Radon test kits are inexpensive ($15-50), and the test itself is straightforward—but there are important differences between test types.
Short-Term Tests (2-7 Days)
Quick screening tests that give you an initial reading. Good for real estate transactions or when you need fast results.
Pros:
- • Fast results (2-7 days of exposure + lab time)
- • Inexpensive ($15-30)
- • Good for home buying decisions
Cons:
- • Less accurate than long-term tests
- • Can be affected by weather, HVAC use
- • May not reflect annual average
Long-Term Tests (90+ Days)
More accurate tests that measure radon over months, accounting for seasonal variations and normal living conditions.
Pros:
- • Most accurate measurement of annual average
- • Accounts for seasonal fluctuations
- • Better for mitigation decisions
Cons:
- • Takes 3-12 months to complete
- • Slightly more expensive ($25-50)
- • Too slow for home buying timeline
EPA Recommended Testing Protocol:
- 1.Start with a short-term test in the lowest lived-in level of your home (usually basement or ground floor)
- 2.Place the test in a frequently used room—not a storage area, bathroom, or kitchen
- 3.Follow closed-house conditions—keep windows and exterior doors closed 12 hours before and during the test (normal entry/exit is fine)
- 4.If results are 4 pCi/L or higher, conduct a follow-up test (either another short-term test or a long-term test) to confirm
- 5.If results are 2-4 pCi/L, consider a long-term test for a more accurate annual average
When to Test:
- • Before buying a home (include radon testing in your inspection contingency)
- • Every 2 years in existing homes (radon levels can change over time)
- • After major renovations (especially foundation work, new HVAC, or room additions)
- • After natural disasters (earthquakes, floods, or settling can create new foundation cracks)
- • When moving into a new home (even if the previous owner tested, re-test to establish a baseline)
Not Sure Which Radon Test Kit to Buy?
We analyzed the top 5 EPA-approved radon test kits sold on Amazon, comparing accuracy, speed, lab fees, and real customer reviews. Our buying guide shows you which kit is right for your situation—whether you're screening before a home purchase, confirming borderline results, or testing after mitigation.
Compare Best Radon Test KitsUnderstanding Your Radon Test Results
Radon is measured in picocuries per liter of air (pCi/L). This measurement represents the number of radioactive decay events happening in one liter of air. The EPA has established 4.0 pCi/L as the "action level"—the point at which mitigation is recommended.
0-2 pCi/L: Low Risk
This is close to the average outdoor radon level (0.4 pCi/L) and the average indoor level nationwide (1.3 pCi/L). No immediate action needed, but consider retesting every 2-5 years. Even at these levels, there is still some lung cancer risk, but it's comparable to normal background radiation exposure.
2-4 pCi/L: Moderate Risk
You're above the national average. The EPA suggests considering mitigation, especially if you plan to live in the home long-term. At 2.7 pCi/L, your lung cancer risk starts to exceed average outdoor exposure risk.
Recommended action: Conduct a long-term test to get an accurate annual average. If confirmed at 2.7+ pCi/L, strongly consider mitigation—especially if there are children in the home or if anyone smokes.
4-10 pCi/L: High Risk
The EPA recommends mitigation at this level. Living in a home with 4 pCi/L for a lifetime gives you roughly the same lung cancer risk as smoking half a pack of cigarettes per day. At 10 pCi/L, the risk is equivalent to smoking a full pack per day.
Recommended action: Mitigate as soon as reasonably possible. This level warrants hiring a certified radon mitigation professional. DIY fixes may help but professional systems are more reliable.
10+ pCi/L: Very High Risk
Immediate action required. At 20 pCi/L, your lung cancer risk is roughly 35-40 times higher than the national average. Some homes test above 100 pCi/L—these are emergency situations.
Recommended action: Contact a certified radon mitigation professional immediately. Consider reducing time spent in the highest-radon areas (usually basement) until a system is installed. Most mitigation systems can reduce levels by 90% or more.
Important Notes About Radon Levels:
- • Radon levels fluctuate daily and seasonally. Winter readings are often higher because houses are closed up.
- • A single test is a snapshot. Follow-up testing confirms that initial results weren't an anomaly.
- • Different rooms can have different levels. Test the lowest lived-in level first, but consider testing other floors too.
- • New construction or renovations can change radon levels. Always retest after major work.
- • There is no "safe" level—only risk reduction. Even 2 pCi/L carries some risk compared to outdoor air (0.4 pCi/L).
Radon Mitigation: Fixing the Problem
If your radon levels are 4 pCi/L or higher, the EPA recommends installing a radon mitigation system. These systems are highly effective—most reduce radon levels by 90% or more. A typical system installation takes 3-6 hours and costs $800-2,500 depending on your home's construction and location.
How Mitigation Systems Work
Active Soil Depressurization (Most Common)
This is the gold standard for radon mitigation. A contractor drills a hole through your basement floor into the soil beneath, inserts a PVC pipe, and runs it up through the house to exhaust above the roofline. A specialized fan in the attic or garage pulls radon-laden air from beneath the foundation and vents it safely outside—before it can enter your home.
System Components:
- • Suction pit beneath the foundation slab
- • 3-4 inch PVC vent pipe running to roof
- • Specialized radon fan (runs 24/7)
- • Warning device to alert if fan fails
- • Sealing of major foundation cracks
Other Mitigation Methods:
- Crawl Space Membrane: For homes with crawl spaces, a heavy plastic sheet covers the soil, with a vent pipe pulling radon from underneath
- Drain Tile Suction: If your home has perimeter drain tiles, these can be used as the collection point instead of drilling through the slab
- Block Wall Suction: For homes with hollow block foundation walls, suction can be applied to the wall cavities
- Heat Recovery Ventilator (HRV): Whole-house ventilation system that exchanges indoor air with outdoor air while recovering heat (less common, used when soil methods won't work)
Cost Breakdown:
- • Typical Installation: $800-2,500
- • Simple slab system: $800-1,500
- • Complex multi-suction system: $1,500-2,500
- • Crawl space system: $1,000-2,000
- • Annual electricity cost: $50-150 (fan runs continuously)
- • Maintenance: Minimal—fan replacement every 10-15 years ($200-400)
Prices vary significantly by region. Get 2-3 quotes from certified radon professionals.
DIY Mitigation: Proceed With Caution
Some homeowners attempt DIY radon reduction by sealing cracks, improving ventilation, or installing their own suction systems. While these methods can work, they're unreliable without proper testing and expertise.
The risk: Improper installation can actually increase radon levels by changing air pressure dynamics in your home. If you're at 8 pCi/L and DIY mitigation doesn't work, you've wasted time living in a high-radon environment. For levels above 4 pCi/L, hire a certified professional. It's worth the cost.
Find Certified Radon Professionals in Your Area
Every state has certification programs for radon testing and mitigation contractors. Always verify credentials before hiring. Look for:
- • State certification or license number
- • National Radon Proficiency Program (NRPP) or National Radon Safety Board (NRSB) certification
- • Proof of insurance and bonding
- • Written estimates and warranties (typically 5 years on system performance)
- • Post-mitigation testing included in quote
Common Radon Questions
Does radon mitigation lower home value?
No—actually the opposite. A properly installed radon mitigation system is seen as a selling point, not a defect. It shows you've proactively addressed a known issue. Homes without mitigation in high-radon areas are more likely to face buyer concerns and negotiation.
Can I test during summer, or must I wait for winter?
You can test any time of year. Winter tests often show higher results because houses are closed up, but that's actually when you're exposed to the highest levels. If you test in summer and get high results, you definitely have a problem. If summer results are moderate (2-4 pCi/L), consider a winter follow-up test.
Will opening windows reduce radon?
Opening windows temporarily reduces radon levels while they're open, but the gas returns as soon as you close them. This isn't a solution—you can't keep windows open year-round, and it doesn't address the source. The only permanent fix is a mitigation system.
My neighbor tested low. Does that mean my house is fine?
No. Radon levels can vary dramatically even between identical houses next door to each other. Soil composition, foundation cracks, ventilation patterns, and construction details all affect radon entry. Always test your own home.
Does a basement apartment or rental unit need separate testing?
Yes. Basement units typically have higher radon levels than upper floors. If you're a landlord, many states require radon disclosure or testing for rental properties. Even if not legally required, it's the right thing to do—and it protects you from liability.
Can radon enter through well water?
Yes, but it's less common. Radon dissolved in well water is released into indoor air when you shower, run the dishwasher, or do laundry. The EPA estimates that 10,000 pCi/L in water contributes about 1 pCi/L to indoor air. Water treatment systems (aeration or activated carbon) can remove radon from water.
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