You can’t see, smell, or taste radon, so the only way to know if it’s in your home is to test for it. Testing is simple, inexpensive, and something any homeowner can do without professional help. The EPA recommends that every home be tested, regardless of location or age, because radon levels vary dramatically even between neighboring houses.
Why Radon Matters
Radon is a radioactive gas that forms naturally as uranium in soil and rock breaks down. It seeps into homes through cracks in foundations, gaps around pipes, and other openings where the building meets the ground. Once inside, it gets trapped and accumulates to concentrations far higher than what you’d encounter outdoors.
Long-term exposure to elevated radon is the leading cause of lung cancer among people who have never smoked. The CDC estimates radon causes roughly 2,900 lung cancers per year in nonsmokers alone, and the total across all groups is significantly higher. The risk compounds dramatically for smokers: a smoker living in a high-radon home faces a far greater chance of lung cancer than either risk factor would produce on its own. Because radon exposure produces no immediate symptoms, testing is the only early warning you’ll get.
Where Radon Risk Is Highest
The EPA divides the country into three radon zones based on geology and existing test data. Zone 1 (highest potential) covers areas where average indoor levels may exceed 4 pCi/L, the concentration at which the EPA says homes should be fixed. Zone 2 represents moderate potential, with average levels between 2 and 4 pCi/L. Zone 3 is the lowest risk category, with averages below 2 pCi/L. You can look up your county on the EPA’s radon zone map.
But here’s the important part: these zones reflect averages, not guarantees. Homes in Zone 3 can test high, and homes in Zone 1 can test low. Soil composition, foundation type, ventilation habits, and even weather patterns all influence what ends up in your air. Your neighbor’s result tells you very little about your own home. The only reliable answer comes from testing your specific house.
Short-Term vs. Long-Term Testing
Radon tests fall into two categories, and which one you need depends on your situation.
Short-term tests run for two to ten days and give you a quick snapshot. They’re the standard choice during real estate transactions and work well as an initial screening. Most guidance recommends a minimum of four days for a reliable reading. These tests are cheap (often under $20 for a mail-in kit) and widely available at hardware stores and online. The trade-off is accuracy: short-term results can miss seasonal swings. Radon concentrations fluctuate with weather, soil moisture, and how much you open your windows, so a four-day test in July may look quite different from one in January.
Long-term tests run for three months or more and capture a much more reliable picture of your average exposure. They smooth out the day-to-day and seasonal fluctuations that can throw off a short reading. If you’re not in a rush, a long-term test gives you the most trustworthy number to base decisions on. Research consistently finds that longer testing periods, three months at minimum, are crucial for reliable results in areas with potential for elevated radon.
A practical approach: start with a short-term test. If the result comes back at or above 4 pCi/L, follow up with either a second short-term test or a long-term test to confirm before investing in mitigation.
Types of Test Devices
Most homeowners will use a passive test kit, meaning it doesn’t need electricity or batteries. The two most common types are charcoal canisters and alpha track detectors. Charcoal canisters absorb radon over a few days and are then mailed to a lab for analysis. Alpha track detectors work similarly but are designed for longer exposure periods. Both are easy to handle and install, though they can be sensitive to temperature, humidity, and airflow in the room.
Electronic continuous monitors are the active alternative. They plug into a wall outlet and measure radon levels hour by hour, letting you see how concentrations change over time. They’re more expensive (several hundred dollars to purchase, or available for rent) and generally need periodic calibration, but they give you real-time data instead of a single averaged number. Professional radon inspectors typically use these during home inspections.
How to Place Your Test Kit
Where and how you set up the test matters as much as which test you choose. Poor placement can give you a misleadingly low or high reading.
- Choose the right floor. Place the kit in the lowest level of your home where people actually spend time. That’s usually a finished basement, a ground-floor living room, or a playroom. An unfinished crawl space doesn’t count.
- Set it on a stable surface. Use a table, shelf, or countertop at least 20 inches above the floor. Don’t put it directly on the ground.
- Keep it away from openings. Position the kit at least 3 feet from any exterior door or window, and at least 1 foot from any exterior wall. Keep it 4 inches away from other objects.
- Avoid drafts and moisture. Stay away from kitchens, bathrooms, laundry rooms, and HVAC vents. Air movement and humidity can interfere with the reading.
Closed-House Conditions
For a short-term test to produce an accurate result, you need to maintain what’s called “closed-house conditions.” This means keeping all exterior doors and windows shut for at least 12 hours before you open the test kit, and keeping them closed for the entire testing period. You can still enter and exit through doors normally, and you should run your heating or air conditioning as usual. What you shouldn’t do is open windows for ventilation, run whole-house fans, or use a fireplace during the test. These all pull outdoor air in and can artificially lower your reading.
What Your Results Mean
Radon is measured in picocuries per liter of air (pCi/L). Here’s how to interpret your number:
- 4 pCi/L or higher: The EPA recommends fixing your home. This is the official action level.
- 2 to 4 pCi/L: The EPA recommends considering mitigation. There is no known safe level of radon exposure, so reducing concentrations in this range still lowers your risk.
- Below 2 pCi/L: Generally considered low risk, though some radon is present in virtually every home. The average outdoor concentration is about 0.4 pCi/L.
If your first short-term test comes back at 4 pCi/L or above, confirm the result before moving to mitigation. A second short-term test or a long-term test will tell you whether that initial number reflects your home’s typical level or just a temporary spike.
Don’t Forget Your Water
If your home uses a private well, radon can also enter through your water supply. When you shower, wash dishes, or run the tap, dissolved radon escapes into the air. The EPA recommends testing private well water for radon, though there is currently no federally enforced drinking water standard for it. Municipal water systems that draw from surface sources like reservoirs generally have very low radon levels, so this is primarily a concern for well users.
If your well water tests high, point-of-entry treatment systems can remove radon before it reaches your faucets. The two main options are aeration devices, which bubble air through the water to strip out the gas, and granular activated carbon filters. Both are installed where the water line enters your home.
What Fixing a Radon Problem Looks Like
The most common and effective solution is called active soil depressurization. A contractor installs a PVC pipe through your basement floor or into your crawl space, connected to a fan that continuously pulls radon-laden air from beneath your foundation and vents it above your roofline. The system runs quietly, uses about as much electricity as a light bulb, and typically costs between $1,000 and $3,000 for a standard single-family home. Most installations take less than a day.
After installation, you should test again to confirm that levels have dropped below 4 pCi/L, and ideally below 2. Retesting every two years or so is a good habit, since foundation settling, soil changes, and system wear can affect performance over time.
Finding a Qualified Contractor
If your results call for mitigation, you’ll want a contractor with proper certification. The EPA points homeowners to two national proficiency programs: the National Radon Proficiency Program (NRPP) and the National Radon Safety Board (NRSB). Both maintain searchable directories of certified professionals. Some states also have their own licensing or certification requirements for radon service providers, so check with your state radon contact through the EPA’s website to find out what credentials are required where you live. Getting quotes from two or three certified contractors before committing is standard practice.