Radon Testing
A complete guide to short-term and long-term radon testing — what each method costs, when to use it, and how to interpret your results so you can protect your family.
Fast Facts: Radon Testing at a Glance
- EPA action level: 4.0 pCi/L — take action at or above this threshold
- DIY test kit cost: $10–$50 (includes lab analysis)
- Professional testing cost: $125–$400 (required for most real estate transactions)
- Short-term test: 2–7 days (some devices up to 90 days)
- Long-term test: 90 days to 1 year — the EPA gold standard for accuracy
- How often to test: Every 2 years minimum, plus after any renovation
- Homes at risk: ~1 in 15 U.S. homes has elevated radon levels
Sources: U.S. EPA, U.S. Surgeon General, CDC, American Lung Association
Why Testing for Radon Is Non-Negotiable
Radon is a naturally occurring radioactive gas that seeps into homes from the soil below. It is colorless, odorless, and tasteless — completely undetectable by human senses. The only way to know if your home has dangerous radon levels is to test for it.
That matters because radon is not a minor environmental nuisance. It is the second leading cause of lung cancer in the United States and the leading cause of lung cancer among people who have never smoked.
Source: U.S. EPA — Assessment of Risks from Radon in Homes
The EPA and the U.S. Surgeon General recommend testing all homes below the third floor for radon. Testing is simple, inexpensive, and takes only a few minutes to set up. There is no reason not to do it.
Source: U.S. EPA — National Residential Radon Survey
Who Should Test for Radon?
The short answer: everyone with a home, workplace, or building they are responsible for. Here are the specific groups who should prioritize testing:
Short-Term vs. Long-Term Radon Tests Compared
Radon tests fall into two categories based on duration. Each has distinct advantages depending on your situation and urgency level.
| Feature | Short-Term Test | Long-Term Test |
|---|---|---|
| Duration | 2–7 days (some devices up to 90 days) | 90 days to 1 year |
| Accuracy | Moderate — captures a snapshot, not a trend | High — reflects true annual average EPA Gold Standard |
| Common Devices | Charcoal canisters, electret ion chambers, continuous radon monitors (CRM) | Alpha track detectors, electret detectors, digital CRMs |
| Cost (DIY) | $10–$30 | $25–$50 |
| Cost (Professional) | $125–$400 | $150–$350 |
| Best Use Case | Initial screening, real estate transactions, post-mitigation verification | Establishing a true baseline, confirming elevated short-term results, ongoing monitoring |
| Closed-House Conditions | Required — 12 hours before and during test (especially for tests < 1 week) | Not strictly required for full duration (natural conditions are acceptable) |
| EPA Recommendation | Start here; if ≥ 4 pCi/L, follow up with a second test | Most accurate measure of actual year-round exposure |
The EPA recommends starting with a short-term test. If results are 4 pCi/L or higher, follow up with either a second short-term test or a long-term test to confirm. For real estate transactions, two simultaneous short-term tests are the standard protocol.
DIY Testing Kits vs. Hiring a Certified Radon Tester
You have two options when it comes to testing: purchase an inexpensive kit and do it yourself, or hire a certified professional with calibrated equipment. The right choice depends on your goals.
| Feature | DIY Test Kit | Professional Testing |
|---|---|---|
| Estimated Cost | $10–$50 Budget | $125–$400 Recommended |
| How It Works | Place passive device (charcoal canister or alpha track) in lowest livable level; mail to lab for analysis | Certified tester deploys continuous radon monitor (CRM); records hourly data for 48+ hours; provides detailed report |
| Accuracy | Moderate — susceptible to user error and environmental interference | High — calibrated instruments with hourly data and tamper detection |
| Turnaround | 1–2 weeks (includes lab processing) | 48 hours to a few days (results often same-day) |
| Pros | Very affordable; available at hardware stores and online; some states offer free kits; good for initial screening | Highest accuracy and reliability; detects test interference; legally defensible results; chain-of-custody documentation; required for real estate in most states |
| Cons | Not accepted for most real estate transactions; susceptible to placement and timing errors; no tamper detection; single data point (no hourly trends) | Higher cost; must schedule with a professional; availability varies by area |
| Ideal For | Peace of mind, initial screening, routine check-ups, budget-conscious homeowners | Real estate transactions, post-mitigation verification, legal documentation, high-accuracy needs |
For routine screening, a DIY kit is perfectly fine as a first step. If results come back at or above 4 pCi/L, follow up with professional testing to confirm. For any real estate transaction, professional testing is almost always required — and well worth the investment.
Source: U.S. EPA — State Radon Programs
How to Test Your Home for Radon: Step-by-Step
Whether you are using a DIY kit or preparing for a professional test, the core protocol is the same. Here is the EPA-recommended process:
Choose Your Test Type
Pick a short-term or long-term test based on your needs. For a quick screening, a 2–7 day charcoal canister kit works well. For real estate, hire a certified professional with a continuous monitor.
Establish Closed-House Conditions
Close all windows and exterior doors at least 12 hours before starting the test. Keep them closed for the entire test duration. Operate heating and cooling systems normally, but avoid running whole-house fans.
Place the Test Device Correctly
Deploy the test in the lowest regularly occupied level of your home — typically a basement or ground floor. Place it in a lived-in room (living room, bedroom, den), at least 20 inches off the floor. Avoid kitchens, bathrooms, and areas near exterior doors, windows, sump pumps, or heating vents.
Leave the Test Undisturbed
Do not move, cover, or disturb the device during the test period. Maintain closed-house conditions throughout. Live normally in the home — just keep exterior openings sealed.
Send to Lab or Review Results
For DIY kits, seal and mail to the lab immediately after the test period ends. Results typically arrive within 1–2 weeks. For professional CRMs, your tester retrieves the device and provides a detailed hourly report.
Interpret Results & Take Action
If results are below 2 pCi/L, no immediate action is needed. Between 2–4 pCi/L, consider mitigation. At 4 pCi/L or above, the EPA recommends taking action to reduce radon. Follow up with a second test to confirm.
Radon Testing for Real Estate Transactions
Real estate radon testing follows stricter protocols than standard home testing. The EPA recommends that all homes be tested for radon at point of sale, regardless of geographic location or radon zone.
In most states, a real estate radon test must be performed by a certified radon measurement professional using a continuous radon monitor (CRM). The professional deploys the device under tamper-evident conditions, ensures the 12-hour closed-house pre-test period is maintained, and provides a certified report suitable for legal documentation.
Real estate radon testing typically costs $150–$400, depending on the market and how many test locations are needed. The test usually runs for a minimum of 48 hours. For homes with multiple foundation types (e.g., a basement plus a crawl space), a separate test in each area is required.
The FHA home inspection form (HUD-92564-CN) includes a specific section on radon testing, and it must be provided to all FHA-insured borrowers. If radon mitigation is needed, it can be financed through a HUD 203(k) mortgage loan.
How to Read & Interpret Your Radon Test Results
Radon levels are measured in picocuries per liter of air (pCi/L). Here is what your results mean and what action to take at each level:
| Your Result | Risk Level | Recommended Action |
|---|---|---|
| Below 2 pCi/L | Low | No immediate action required. Re-test every 2 years or after any renovation. |
| 2–4 pCi/L | Moderate | Consider mitigation. The WHO recommends action above 2.7 pCi/L. Re-test to confirm. |
| 4 pCi/L or above | Elevated — Action Required | EPA recommends mitigation. Confirm with a follow-up test (short-term or long-term). Contact a certified radon contractor. |
| 10+ pCi/L | High | Prioritize mitigation immediately. Consider interim measures (increased ventilation) while system is installed. |
For context, the average indoor radon level in U.S. homes is approximately 1.3 pCi/L. The average outdoor level is about 0.4 pCi/L. Any amount of radon exposure carries some risk, but the EPA considers 4 pCi/L the threshold where the cost of mitigation becomes clearly justified by the health benefit.
If your initial short-term test returns a result of 4 pCi/L or higher, the EPA recommends confirming with either a second short-term test or a long-term test before committing to mitigation. However, if levels are significantly elevated (10+ pCi/L), take immediate action.
How Often Should You Test for Radon?
The EPA recommends testing your home at least every two years, even if previous results were low. Radon levels can change over time due to shifts in soil conditions, foundation settling, changes in home ventilation, and seasonal weather patterns.
You should also re-test if any of the following occur: you complete a major renovation or structural change to your home; you begin spending significant time on a previously unused level (e.g., finishing a basement); you install or modify a radon mitigation system; or you notice new cracks in your foundation.
If you already have a radon mitigation system in place, test within 30 days of activation to confirm the system is working, then continue testing on the standard two-year schedule.
How Accurate Are Home Radon Test Kits?
DIY charcoal canister kits provide a reasonable screening-level estimate, but they are not as precise as professional testing. The main accuracy limitations include sensitivity to humidity and temperature, potential for user error during placement and retrieval, and the fact that a 2–7 day snapshot may not represent year-round conditions.
Professional continuous radon monitors (CRMs) are significantly more accurate. They record hourly data, detect unusual fluctuations that might indicate test interference, and produce a detailed time-series report. CRMs are the standard for real estate testing and post-mitigation verification.
Long-term alpha track detectors (90+ days) offer the best balance of affordability and accuracy for homeowners who are not in a rush. Because they average radon exposure over an extended period, they smooth out the daily and seasonal fluctuations that can make short-term results misleading.
Consumer-grade digital monitors fall between DIY kits and professional CRMs in accuracy. They are excellent for ongoing monitoring but most are not certified for real estate use in states that require it.
When Is the Best Time of Year to Test for Radon?
Radon levels in most homes are highest during the colder months. Winter conditions — sealed windows, closed doors, and heating systems that create a "stack effect" — pull soil gas into the home more aggressively. Testing during winter typically captures your worst-case exposure scenario.
That said, the EPA recommends testing regardless of season. Any test is better than no test. If you run a short-term test in summer and the results are elevated, winter levels are almost certainly higher.
For the most comprehensive picture, deploy a long-term test that spans at least one full heating and cooling cycle (ideally winter through summer). This gives you a true annual average.
Check Radon Testing Data Near You
Radon testing urgency depends heavily on where you live. Homes built over granite, shale, and phosphate-bearing soils tend to have significantly higher radon levels than homes on sandy or clay-heavy soils. Local weather patterns, water tables, and building practices all play a role too.
RadonResources.com maintains a large database of user-submitted radon test results, combined with USGS geological survey data and EPA zone classifications — broken down to the state, metro, and city level.
Before you test, check your area's historical data. Browse service areas by state, explore city and metro pages, and request a free quote to connect with certified testers and contractors near you.
Explore Radon Data by State
Frequently Asked Questions
How often should I test my home for radon?
The EPA recommends testing at least every two years. You should also re-test after any renovation, structural change, or change in which level of your home you occupy most. If you have a mitigation system, test within 30 days of activation and then every two years.
How accurate are home radon test kits?
DIY charcoal canister kits provide a reasonable snapshot but are susceptible to user error and environmental factors. Professional continuous radon monitors (CRMs) offer the highest short-term accuracy with hourly readings and tamper detection. For the best long-term accuracy, the EPA considers 90+ day alpha track detectors the gold standard.
What is the EPA action level for radon?
The EPA action level is 4.0 pCi/L (picocuries per liter). Homes at or above this level should take action to reduce radon. The EPA also recommends considering mitigation for levels between 2 and 4 pCi/L. The World Health Organization recommends a stricter threshold of 2.7 pCi/L (100 Bq/m³).
Do I need a professional radon test for a real estate transaction?
In most states, yes. Real estate radon tests must be conducted by a certified measurement professional using a continuous radon monitor under strict chain-of-custody protocols. DIY test kits are generally not accepted. Professional real estate testing typically costs $150–$400 and runs for a minimum of 48 hours.
When is the best time of year to test for radon?
Radon levels tend to peak during colder months when homes are sealed tightly. Winter testing often captures worst-case conditions. However, the EPA recommends testing regardless of season — any test is better than no test. For the most accurate annual average, use a long-term test spanning multiple seasons.
How long does a radon test take?
Short-term tests take 2 to 7 days (some devices up to 90 days). Long-term tests run for 90 days to one full year and provide the most accurate picture of annual exposure. Professional real estate tests using continuous monitors typically run 48 hours minimum.
Can I test for radon myself?
Yes — DIY radon test kits are widely available at hardware stores, home improvement centers, and online for $10–$50. Many state radon programs also offer free kits. However, for real estate transactions and official documentation, professional testing is required in most states.
Where should I place a radon test in my home?
Place the test in the lowest regularly occupied level of your home — typically a basement or ground-floor living area. Position it at least 20 inches above the floor in a room where you spend time. Avoid kitchens, bathrooms, laundry rooms, and areas near windows, sump pumps, exterior doors, or HVAC vents.