Radon Levels by ZIP Code
Check your area's EPA radon zone and testing data. Free, instant, science-backed.
Franklin County, OH
EPA Zone 1 — Predicted indoor radon >4 pCi/L
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Understanding Radon Risk
Radon is a naturally occurring radioactive gas that seeps into homes from the ground. It's the #1 cause of lung cancer among non-smokers, responsible for about 21,000 deaths per year in the United States. You can't see, smell, or taste radon — testing is the only way to know.
What Is Radon Gas?
Radon (Rn-222) is a naturally occurring radioactive gas produced by the decay of uranium, which is found in nearly all soils and rock formations worldwide. Unlike most radioactive elements, radon is a gas at room temperature, allowing it to move freely through soil and enter buildings through openings in the foundation.
Radon is completely invisible — you cannot see, smell, or taste it. It has a half-life of 3.8 days, meaning it continuously regenerates from uranium deposits in the ground. This is why radon levels can never be permanently "cleared" — only managed through ventilation and mitigation systems.
The uranium decay chain: Uranium-238 in soil decays through radium into radon gas, which seeps upward into buildings.
Every home in the United States has some level of radon. The concentration depends on local geology (uranium content in soil), soil permeability, building construction, weather patterns, and ventilation. Two homes on the same street can have vastly different radon levels.
How Radon Enters Your Home
Indoor air pressure is typically lower than the pressure in the soil surrounding your foundation. This pressure difference acts like a vacuum, drawing radon gas upward through any available opening. Warm air rising inside your home (the "stack effect") and exhaust fans further increase this suction.
Foundation Cracks
Even hairline cracks in poured concrete or block foundations create pathways for radon to migrate from the soil into basements and lower levels.
Construction Joints
Gaps where walls meet the floor slab, and mortar joints in concrete block walls, are among the most common radon entry points.
Sump Pits & Floor Drains
Uncovered sump pits and floor drains connected to soil beneath the home provide a direct, open pathway for radon gas to enter.
Pipe & Utility Penetrations
Gaps around plumbing pipes, electrical conduits, and other utilities that penetrate the foundation slab allow soil gas infiltration.
Radon in Your Basement
Basements and ground-floor rooms typically have the highest radon concentrations because they are closest to the soil. However, radon does not stay in the basement — it migrates to upper floors through stairways, elevator shafts, HVAC ductwork, and gaps in flooring. Upper floors generally have lower levels, but testing should always occur on the lowest livable level of your home.
Can Apartments, Condos & New Homes Have Radon?
Yes. Any building in contact with the ground can have elevated radon, regardless of age or construction type. Ground-floor and basement apartments are most at risk, but radon has been found in upper-floor units through shared ventilation systems and utility chases. New construction is not immune — modern tight-sealed homes can actually trap more radon indoors. The EPA recommends that all homes, including new builds, be tested.
Health Effects & Symptoms of Radon Exposure
The World Health Organization classifies radon as a Group 1 carcinogen — the highest danger classification, in the same category as asbestos and tobacco smoke. Radon is the second leading cause of lung cancer in the United States, and the #1 cause of lung cancer among people who have never smoked.
Does Radon Cause Immediate Symptoms?
No. Radon exposure produces no immediate symptoms — no headaches, nausea, or fatigue. This is precisely what makes it so dangerous: you can be exposed for years without any indication. Symptoms of radon-related lung cancer (persistent cough, shortness of breath, chest pain, coughing up blood) typically appear only after prolonged exposure over 5 to 25 years.
Contrary to common belief, radon does not cause headaches, fatigue, or dizziness at typical indoor concentrations. If you experience these symptoms, other causes (carbon monoxide, mold, poor ventilation) should be investigated.
Radon & Smoking: A Dangerous Combination
The combination of radon exposure and smoking increases lung cancer risk dramatically. A smoker exposed to elevated radon has approximately 10 times the risk of a non-smoker with the same radon exposure. According to the EPA, a smoker living in a home with 4 pCi/L has a 1 in 40 lifetime risk of lung cancer, compared to 1 in 270 for a non-smoker. If you smoke and live in a high-radon area, testing and mitigation are especially critical.
Are Pets at Risk?
Yes. Dogs and cats breathe the same indoor air and can develop radon-related health problems. Studies have linked radon exposure to increased rates of lung cancer in dogs. Pets that spend significant time in basements or ground-level rooms may have higher exposure.
Radon Risk by State
Click a state to see county-by-county radon data. Colors show the dominant EPA radon zone.
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Safe & Acceptable Radon Levels
Radon is measured in picocuries per liter (pCi/L) in the United States, or becquerels per cubic meter (Bq/m³) internationally. Understanding the scale helps you interpret your test results and decide when to take action.
The U.S. EPA recommends fixing your home if radon levels are 4.0 pCi/L or higher. At this level, the risk of lung cancer becomes significant over long-term exposure.
The EPA recommends considering mitigation for levels between 2.0 and 4.0 pCi/L, especially if you plan to stay in your home long-term.
The World Health Organization sets a stricter reference level of 100 Bq/m³ (2.7 pCi/L), recommending national action plans to reduce levels below this threshold.
There is no known safe level of radon exposure. Even below 2.0 pCi/L, some risk exists. The average outdoor level is about 0.4 pCi/L, and the average indoor level in the US is 1.3 pCi/L.
Unit conversion: 1 pCi/L = 37 Bq/m³ | 4.0 pCi/L = 148 Bq/m³ | 100 Bq/m³ = 2.7 pCi/L
How to Test Your Home for Radon
Testing is the only way to know your home's radon level. You cannot predict radon based on your neighbor's results, your home's age, or your geographic zone. The EPA recommends testing all homes below the third floor, regardless of location.
Short-Term Test
2 – 7 days
- Charcoal canister or electret ion chamber
- Cost: $10 – $30 (DIY kit)
- Best for quick screening and real estate transactions
- Place on lowest livable level, closed-house conditions
Long-Term Test
90+ days
- Alpha track or electret detectors
- Cost: $20 – $40 (DIY kit)
- Most accurate — accounts for seasonal fluctuations
- Best for year-round average reading
Continuous Monitor
Ongoing
- Electronic monitors (Airthings, RadonEye, Ecosense)
- Cost: $150 – $300 one-time purchase
- Real-time readings with hourly and daily averages
- Best for ongoing monitoring and post-mitigation verification
DIY vs. Professional Testing
DIY test kits are scientifically accurate when instructions are followed correctly. Professional radon tests ($150–$250) use calibrated continuous monitors and are required for some real estate transactions. The EPA states that both approaches are valid for determining radon levels. If your short-term test shows 4 pCi/L or higher, follow up with either a second short-term test or a long-term test before committing to mitigation.
Reducing Radon in Your Home
If testing confirms elevated radon, effective solutions exist. Professional radon mitigation systems can reduce levels by up to 99%, and even simple improvements can help in moderate cases. The most common and effective approach is Active Soil Depressurization (ASD).
Active Soil Depressurization: A pipe and fan system draws radon from beneath the foundation and vents it safely above the roofline.
Sub-Slab Depressurization
The most common method. A pipe is inserted through the foundation slab into the gravel or soil beneath. A continuously running fan creates suction, pulling radon gas out before it can enter your home and venting it above the roof.
Effectiveness: up to 99% | Cost: $800 – $1,500Sub-Membrane Depressurization
Used for homes with dirt-floor crawl spaces. A durable plastic membrane is sealed over the earth floor, and a fan draws radon from beneath the membrane through a vent pipe to the exterior.
Effectiveness: 90–99% | Cost: $1,000 – $2,500Sealing & Improved Ventilation
Sealing foundation cracks, covering sump pits, and improving basement ventilation can help reduce moderate radon levels. However, sealing alone is not a reliable long-term solution according to EPA guidance and should supplement, not replace, active depressurization.
Effectiveness: variable | Cost: $200 – $500DIY Radon Reduction Tips
Before investing in professional mitigation, homeowners with moderate levels (2.0 – 4.0 pCi/L) can try these steps: seal visible cracks in the basement floor and walls with polyurethane caulk, cover exposed sump pits with airtight lids, ensure crawl spaces are properly sealed, and improve basement ventilation. These measures may reduce radon by 20–50%, but re-test after any changes to verify their effectiveness. If levels remain above 4.0 pCi/L, professional mitigation is strongly recommended.
What Does Mitigation Cost?
Most residential radon mitigation systems cost between $800 and $2,500, depending on your home's foundation type, size, and local labor rates. The fan typically lasts 10–15 years and costs $150–$300 to replace. Mitigation costs are often recoverable in home resale value, and some states offer tax credits or assistance programs for radon mitigation.
Radon When Buying or Selling a Home
Radon is a growing consideration in real estate transactions. Understanding your obligations and options can help you navigate the process smoothly, whether you are a buyer, seller, or real estate professional.
For Home Buyers
- Always request a radon test during the inspection period — even if the seller has previous test results
- A radon test typically takes 48+ hours using a continuous monitor
- If levels exceed 4.0 pCi/L, you can negotiate for the seller to install mitigation before closing, or request a price reduction to cover costs
- A failed radon test is not a deal-breaker — mitigation is straightforward and costs $800–$1,500
For Home Sellers
- Pre-test and mitigate before listing to avoid delays and buyer concerns
- Disclosure requirements vary by state — some states require sellers to disclose known radon levels
- A mitigation system can be a selling point, showing buyers the home has been proactively addressed
- Keep test results and mitigation receipts for buyer review
Radon Disclosure Laws
Several states (including Illinois, Colorado, Florida, Maine, and others) require sellers or landlords to disclose known radon test results or provide radon information pamphlets. Even in states without mandatory disclosure laws, failing to disclose known hazards can create legal liability. Check your state's radon program for specific requirements.
Radon in Water
Radon can dissolve in groundwater, particularly in private wells drilled into granite or other uranium-bearing rock. When radon-contaminated water is used for showering, washing dishes, or other household purposes, the gas is released into the indoor air. The EPA estimates that radon in water contributes about 1–2% of total indoor radon on average, but individual homes with very high water radon levels can see a more significant contribution.
Testing for radon in water requires a separate test from air testing — a standard radon test kit will not detect waterborne radon. Water treatment options include aeration systems (which bubble air through the water to release radon before it enters your home) and granular activated carbon filters (which absorb radon from the water). If you have a private well in a high-radon area, consider testing your water in addition to your indoor air.
Frequently Asked Questions
What is radon and why is it dangerous?
Radon is a colorless, odorless radioactive gas that forms naturally from the decay of uranium in soil and rock. It seeps into buildings through cracks in foundations. Prolonged exposure to elevated radon levels is the second leading cause of lung cancer in the US, responsible for about 21,000 deaths annually.
What are the EPA radon zones?
The EPA classifies every US county into three zones. Zone 1 (high risk) has predicted average indoor radon above 4 pCi/L. Zone 2 (moderate) is between 2-4 pCi/L. Zone 3 (low) is below 2 pCi/L. These predictions are based on geology, soil permeability, building construction, and indoor radon measurements.
What is the EPA action level for radon?
The EPA recommends taking action to reduce radon in your home if levels are at or above 4.0 pCi/L (picocuries per liter of air). The EPA also suggests considering action for levels between 2.0 and 4.0 pCi/L. There is no known safe level of radon exposure.
Should I test my home for radon?
Yes. The EPA recommends that all homes be tested for radon, regardless of geographic location or zone designation. Even homes in low-risk Zone 3 areas can have elevated radon. Short-term test kits are inexpensive and available at most hardware stores.
Can radon levels vary within the same ZIP code?
Yes, significantly. Radon levels depend on local soil composition, home construction type, foundation condition, and ventilation. Two homes on the same street can have very different radon levels. Our data shows county-level averages — individual home testing is essential.
How can I reduce radon in my home?
Radon mitigation systems use a vent pipe and fan to pull radon from beneath the house and vent it outside. These systems can reduce radon levels by up to 99%. A qualified radon mitigator can install a system typically for $800-$1,500.
Is it safe to live in a house with radon?
All homes have some level of radon. The question is whether the level is elevated. Homes with radon below 2.0 pCi/L are generally considered low risk. Between 2.0 and 4.0, the EPA suggests considering mitigation. Above 4.0 pCi/L, the EPA recommends taking action. With a properly installed mitigation system, you can reduce radon to safe levels and live comfortably in any home.
How long do you have to be exposed to radon for it to be harmful?
Radon-related lung cancer risk increases with both the concentration level and the duration of exposure. There is no sharp threshold — any exposure carries some risk. However, the primary concern is long-term exposure over years or decades. Short-term exposure (days or weeks) at typical residential levels poses very low risk. The EPA action level of 4.0 pCi/L is based on a lifetime exposure model.
Does radon only stay in the basement?
No. While radon concentrations are typically highest in basements and ground-level rooms because they are closest to the soil, radon migrates to upper floors through stairways, HVAC ductwork, utility chases, and gaps in flooring. Upper floors generally have lower levels, but the entire home can be affected.
Can radon affect apartments and condos?
Yes. Any building in contact with the ground can have radon. Ground-floor and basement apartments are most at risk. Upper-floor units can also be affected if radon travels through shared ventilation systems, elevator shafts, or utility penetrations. If you live in a multi-unit building, request radon testing from your building management.
Is radon testing required when buying a home?
Radon testing is not federally mandated, but many states recommend or require radon disclosure during real estate transactions. Most home inspectors offer radon testing as an add-on. The EPA recommends that all home buyers request a radon test during the inspection period. If levels exceed 4.0 pCi/L, you can negotiate with the seller for mitigation before closing.
What is the difference between EPA and WHO radon guidelines?
The EPA recommends action at 4.0 pCi/L (148 Bq/m³) and suggests considering action at 2.0-4.0 pCi/L. The World Health Organization has a stricter reference level of 100 Bq/m³ (2.7 pCi/L). Both organizations agree that there is no known safe level of radon exposure. The WHO guideline reflects more recent research on radon health effects at lower concentrations.