How to Test Your Home for Radon: Step-by-Step Guide

You test your smoke detectors. You check your carbon monoxide alarm. But there’s a good chance there’s something lurking in your home right now that you’ve never once thought to test for — and it’s the second leading cause of lung cancer in the United States. Radon gas kills roughly 21,000 Americans every year, and the unsettling part is that it’s completely invisible, odorless, and tasteless. The only way to know if your home has a problem is to test. The good news? Testing is inexpensive, easy, and something any homeowner can do this weekend. This guide walks you through exactly how to test your home for radon — from choosing the right test kit to reading your results and knowing what to do next.

Why Radon Testing Matters More Than Most People Realize

Radon is a naturally occurring radioactive gas that forms when uranium in soil and rock breaks down. It seeps up through the ground and enters your home through foundation cracks, gaps around pipes, sump pit openings, and even through poured concrete — which is more porous than it looks. Once inside, it accumulates. Basements and lower levels tend to have the highest concentrations, but radon has been found at dangerous levels in homes without basements too. The EPA has set the action level at 4 pCi/L (picocuries per liter of air). The average indoor radon level in the U.S. sits around 1.3 pCi/L. If your home is above 4 pCi/L, the EPA recommends mitigation. Many experts actually suggest considering action at 2 pCi/L, since no level of radon exposure is considered completely safe.

Here’s the mechanism that makes radon so dangerous. When radon decays, it releases alpha particles — high-energy bursts of radiation. Breathe in radon gas and those alpha particles can strike the delicate cells lining your lungs, damaging DNA in ways that can eventually lead to cancer. Radon itself has a half-life of 3.8 days, but its decay products — polonium, lead, and bismuth isotopes — can attach to dust and aerosols in the air and lodge deep in lung tissue. Most people don’t think about this until they’re sitting across from a doctor discussing a diagnosis. Testing takes that risk off the table early. And if you’ve ever wondered whether your body gives you any warning signs before things get serious, the honest answer is mostly no — radon gas symptoms from exposure are essentially nonexistent until significant damage has already occurred.

The Two Main Types of Radon Tests (And How to Choose)

There are two broad categories of radon tests: short-term and long-term. Short-term tests run anywhere from 2 to 7 days and give you a quick snapshot of radon levels in your home. Long-term tests stay in place for 90 days to a year and measure average radon levels over time, which tends to be more accurate because radon fluctuates with weather, seasons, and how often you open windows. Which one is right for you depends on your situation. If you need results quickly — say, you’re buying or selling a home — a short-term test makes sense. If you’re doing routine testing for your own peace of mind and accuracy matters most, go long-term. Both test types are widely available, affordable (often $15–$50 for DIY kits), and meet NSF/ANSI Standard 269, the national standard for radon measurement devices.

There’s also a third option worth knowing about: continuous electronic radon monitors. These plug-in or battery-operated devices measure radon levels in real time and display hourly or daily readings. They’re more expensive upfront (typically $100–$200) but useful if you want ongoing visibility into your home’s radon levels, especially after mitigation work. For most homeowners doing a first-time test, though, a passive short-term or long-term charcoal canister test is entirely sufficient. Here’s a step-by-step breakdown of how the short-term testing process works:

1. Buy a certified test kit. Look for kits labeled as meeting NSF/ANSI Standard 269, or order through your state’s radon program — many states offer free or discounted kits. Hardware stores like Home Depot and Lowe’s carry them, and they’re also widely available online.
2. Choose the right location. Place the test in the lowest livable area of your home — a finished basement, a ground-floor bedroom, or wherever your family spends the most time at or below ground level. Don’t test in a crawl space, kitchen, bathroom, or laundry room.
3. Set up closed-house conditions. At least 12 hours before the test begins and throughout the testing period, keep windows and doors closed as much as possible. Normal entry and exit is fine. Running central air conditioning or heat is fine too — just don’t run whole-house fans or leave windows open overnight.
4. Place the detector correctly. Hang or set the test kit in the middle of the room, roughly 2–6 feet off the floor. Keep it away from drafts, exterior walls, and high-humidity areas. Don’t place it in a closet or cabinet.
5. Leave it undisturbed for the full test period. For a short-term charcoal canister test, that’s typically 48–96 hours. Don’t move it, and don’t let the kids use it as a hockey puck.
6. Mail it to the lab promptly. Most kits include a prepaid mailer. Send it the same day you close the test. Labs typically return results within a few days, and many now offer online results.

Common Radon Testing Mistakes That Throw Off Your Results

A test is only useful if it gives you accurate information. Radon testing is simple, but there are a handful of easy mistakes that can skew your results significantly — either giving you a false sense of security or sending you into unnecessary panic. The most common error is placing the test in the wrong room. Testing in an unfinished basement that you never use, for example, doesn’t tell you much about your actual exposure. What matters is where you live, sleep, and breathe. A first-floor bedroom where your child sleeps eight hours a night is a more relevant data point than a storage room you visit twice a year.

Weather matters more than most people expect. Radon tends to be higher in winter when homes are sealed tight and soil is frozen (which pressurizes radon upward), and lower in summer when ventilation is more common. A test done during a stretch of unusually warm weather with open windows may significantly underestimate your year-round average. That’s one reason long-term tests are considered more reliable. Watch out for these other common mistakes:

• Testing too high up: Radon is heavier than air and concentrates at lower levels. A test placed on a second floor won’t reflect true exposure in a basement or ground floor.
• Ignoring closed-house conditions: Opening windows during the test period dilutes radon levels artificially. This is the single most common reason test results come back falsely low.
• Testing right after a storm: Barometric pressure changes can temporarily suppress or spike radon levels. Avoid testing immediately after a major weather event if you can.
• Using an expired test kit: Charcoal canisters have a shelf life. Check the expiration date before you deploy it — an old kit gives unreliable results.
• Waiting too long to mail the kit: Charcoal continues to interact with the environment after you close it. Get it in the mail the same day, ideally within 24 hours of closing.

Understanding Your Radon Test Results

Your test results come back as a number — a radon concentration expressed in picocuries per liter (pCi/L). That number tells you how much radioactive decay is happening per liter of air in your home. Now you need to know what to do with it. The EPA’s guidance is widely used, but it’s worth understanding what each range actually means for your family’s risk, not just whether you crossed an arbitrary threshold. The relationship between radon exposure and lung cancer risk is cumulative — meaning it’s about how much you breathe in over months and years, not just a single snapshot number. That said, the table below gives you a practical framework for interpreting your results.

One nuance worth acknowledging: what counts as an acceptable level genuinely depends on the situation. A result of 3.8 pCi/L in a home where no one spends time in the basement is a different scenario than 3.8 pCi/L in a bedroom where someone sleeps. The EPA action level of 4 pCi/L is a policy threshold, not a biological cliff edge. Risk increases steadily with concentration and duration of exposure. If your result is between 2 and 4 pCi/L, mitigation isn’t mandatory but it’s worth serious consideration — especially if you have young children or anyone in the household with existing lung conditions. Understanding how long it takes for radon to cause lung cancer can help put these numbers in context and inform how urgently you choose to act.

Radon Level (pCi/L)	Risk Category	EPA Recommendation	Estimated Lung Cancer Risk (per 1,000 non-smokers over lifetime)
Below 2 pCi/L	Low	No action required; retest every 2 years	~3 per 1,000
2–4 pCi/L	Moderate	Consider mitigation; retest to confirm	~5–9 per 1,000
4–8 pCi/L	Elevated	Mitigate within a few months	~15–17 per 1,000
8–20 pCi/L	High	Mitigate within weeks	~29–37 per 1,000
Above 20 pCi/L	Very High	Mitigate as soon as possible	~36–73 per 1,000

What to Do After Your Radon Test: Next Steps Based on Your Results

If your result comes back below 2 pCi/L, you can breathe easy — though you should retest every two years or any time you make significant changes to your home like finishing a basement, adding a room below grade, or doing major foundation work. If you come back between 2 and 4 pCi/L, the EPA doesn’t require action but recommends considering it. Running a long-term test to confirm your average level is a smart next step. If you’re above 4 pCi/L — whether it’s 4.1 or 40 — you need mitigation. Full stop. The good news is that radon mitigation is a well-established, highly effective process. Sub-slab depressurization, the most common approach, involves installing a pipe and fan system that draws radon from beneath your foundation and exhausts it outside before it can enter your living space. It typically reduces radon levels by 50–99%.

After any mitigation system is installed, you’ll want to retest to confirm it’s working. Retest 24 hours after the system is running, then again 30 days later, and then annually going forward. Mitigation systems need occasional maintenance — the fan can wear out over time — so ongoing testing isn’t optional, it’s part of the deal. When hiring a mitigator, look for certification through the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB). These certifications mean the contractor has passed national exams and follows standardized installation protocols. Don’t let anyone install a mitigation system without those credentials — the work matters too much to cut corners on.

Pro-Tip: If you’re buying a home and the seller provides a radon test result, ask when the test was conducted, what type of test was used, and whether closed-house conditions were maintained. A test done years ago — or done improperly — tells you nothing about current conditions. Always request a fresh test or conduct one yourself during the inspection period. A short-term test kit costs less than $20 and could save you from purchasing a home with a serious radon problem that a seller’s outdated test missed entirely.

“Most homeowners assume their home is safe because it doesn’t show up on a regional map or because their neighbor tested low. Radon doesn’t work that way — two houses on the same street can have dramatically different levels depending on foundation type, soil composition, and interior pressure dynamics. The only way to know your actual exposure is to test your specific home, ideally with a long-term device for the most accurate picture.”

Dr. Patricia Halloran, NRPP-Certified Radon Measurement Specialist and Environmental Health Researcher, University of Minnesota School of Public Health

Testing your home for radon isn’t a complex or expensive project — it’s an afternoon of effort that gives you real information about one of the most significant environmental health risks inside your own four walls. Pick up a certified test kit, place it correctly in your lowest lived-in space, follow the closed-house protocol, and mail it in. If the results are low, great — set a reminder to test again in a couple of years. If they’re elevated, you now know, and you can do something about it. The families that don’t test are the ones who remain at risk not because of bad luck, but because of missing information. Don’t be in that group. Test your home.

Frequently Asked Questions