Radon testing is the single most important thing a homeowner can do about radon—because radon has no smell, no color, and no immediate symptoms. You cannot “sense” it. You can’t reliably predict it from your neighbors’ results or from a map. The only way to know your home’s radon level is to test. (Source: EPA – https://www.epa.gov/radon; Source: CDC – https://www.cdc.gov/radon/about/index.html)
This guide is designed as a dominant pillar article for RadonRN.com. It walks you through exactly how to test, how to choose the right test type, where to place it, what to avoid, how to interpret results, and what to do next. You’ll also find a large FAQ-style section for special situations like basements, crawlspaces, real estate testing, and retesting schedules.
Table of Contents
- Why radon testing matters
- Radon basics: units and the EPA action level
- Short-term vs long-term tests (which should you use?)
- Choosing a radon test method (charcoal, alpha track, digital monitors)
- Step-by-step: how to test your home for radon
- Where to place the test (the #1 place people mess up)
- Closed-house conditions: what they are and when they matter
- Common mistakes that can ruin a radon test
- How to interpret your results
- What to do if your radon is high (next steps)
- Retesting: how often to test and when to re-test
- Testing in special situations (crawlspaces, apartments, new homes, schools)
- Radon testing during real estate transactions
- Professional testing vs DIY: what’s the difference?
- Sources and further reading
1) Why radon testing matters
Radon is a radioactive gas that forms naturally from uranium in soil and rock. Outdoors, it dilutes quickly. Indoors, it can build up—especially in basements and lower levels—where it increases lung cancer risk over long-term exposure. Because you can’t see or smell radon, a home can look perfectly healthy and still have elevated radon. Testing is the only way to know. (Source: CDC – https://www.cdc.gov/radon/about/index.html; Source: EPA – https://www.epa.gov/radon)
It’s also important to understand that radon is a “house-specific” problem. Two homes on the same street can test very differently because radon levels depend on soil gas pathways, the foundation, ventilation patterns, and pressure differences inside the building. That’s why broad radon maps can’t tell you your exact home level. (Source: EPA – https://www.epa.gov/radon/epa-map-radon-zones)
2) Radon basics: units and the EPA action level
In the United States, radon is typically measured in pCi/L (picocuries per liter). The EPA recommends taking action (mitigation) when the radon level is 4.0 pCi/L or higher. EPA also notes there is no known safe level of radon exposure and encourages homeowners to consider reducing levels between 2.0 and 4.0 pCi/L as well. (Source: EPA – https://www.epa.gov/radon/what-epas-action-level-radon-and-what-does-it-mean)
Many other countries use Bq/m³ (becquerels per cubic meter). A commonly used conversion is 1 pCi/L ≈ 37 Bq/m³, which is why EPA’s 4.0 pCi/L action level is often shown as roughly 150 Bq/m³. (Source: EPA – https://www.epa.gov/radon/what-epas-action-level-radon-and-what-does-it-mean)
3) Short-term vs long-term tests (which should you use?)
Radon levels change over time due to weather, ventilation, HVAC operation, and seasonal patterns. That’s why there are two main categories of testing: short-term and long-term. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Short-term radon tests
Short-term tests typically run 2–7 days and are used when you want quick information (for example, during a home sale or when you’re screening a home for the first time). They can be accurate, but they represent a snapshot, not necessarily your year-round average. EPA provides guidance on follow-up testing based on your result. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Long-term radon tests
Long-term tests run 90 days to 1 year. Because they average over many weather and living conditions, they typically provide a more representative estimate of your annual radon level. If you’re not in a hurry, this is often the most “confidence-building” approach. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
So which should you choose?
If you want the best representation of long-term exposure and you have time, choose a long-term test. If you need quick results or you’re testing as part of a transaction timeline, choose a short-term test and follow EPA’s recommendations for confirming results when needed. (Source: EPA – https://www.epa.gov/radon)
4) Choosing a radon test method (charcoal, alpha track, digital monitors)
There are several common radon test technologies. The “best” one depends on how quickly you need results and how much confidence you want in a long-term average.
Charcoal tests (short-term)
Charcoal adsorption kits are widely used short-term tests. Radon is absorbed onto charcoal during the test window, and the kit is mailed to a lab for analysis. They’re affordable and common for first-time testing. EPA recognizes charcoal tests as one of the common short-term methods. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Alpha track detectors (long-term)
Alpha track detectors are common long-term tests. They record damage tracks from alpha radiation over time, which can be counted after the exposure period. This method is well-suited to averaging over seasonal variation. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Electret ion chambers (short or long-term)
Electret tests can be used in both short-term and long-term formats. They measure ionization caused by radiation exposure over the test period. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Digital radon monitors (continuous monitors)
Continuous radon monitors (CRMs) provide readings over time—sometimes hour by hour. They can be helpful to observe patterns (like higher radon overnight or during HVAC cycles). For official decisions (especially in real estate), it’s important to follow recognized protocols and use appropriate devices. (Source: EPA – https://www.epa.gov/radon)
Important note: “Consumer digital monitors” can be useful for tracking trends, but for your first diagnosis of radon level, many homeowners still prefer a lab-analyzed kit or a professional test to establish a baseline confidence. EPA provides general testing guidance and encourages following the instructions of the device used. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
5) Step-by-step: how to test your home for radon
Radon testing is simple, but the details matter. Follow these steps closely for a reliable result.
Step 1: Decide where you want the “truth” to reflect
Test the lowest level of the home that you live in or spend time in. If you never use the basement, but you plan to finish it or use it as an office, test there anyway—because your lifestyle is changing. EPA guidance emphasizes testing the lowest lived-in level. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Step 2: Choose your test type (short-term vs long-term)
If you want quick screening, use a short-term kit. If you want a stable annual average, use a long-term kit. If your short-term result is near decision thresholds, EPA provides guidance on follow-up tests. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Step 3: Prepare the home (especially for short-term tests)
For many short-term tests, you’ll want to maintain closed-house conditions (more details below). Keep windows closed, keep normal heating/cooling running, and avoid unusual ventilation patterns. (Source: EPA home buying radon guidance PDF – https://www.epa.gov/system/files/documents/2024-11/2024-buying-a-new-home-how-to-protect-your-family-from-radon_0.pdf)
Step 4: Place the kit correctly
Place the device in the recommended location: away from drafts, exterior doors, windows, direct sunlight, high heat, and high humidity. Don’t place it on bare concrete unless the instructions allow it—use a table or shelf. Keep it out of reach of children and pets. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Step 5: Run the test for the full required time
Short-term kits are often 2–7 days; long-term tests are 90+ days. Do not shorten the test window. Radon fluctuates, and short tests become less reliable if you don’t follow the intended time period. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Step 6: Seal and send (if it’s a mail-in kit)
For charcoal kits, timing matters. Follow the instructions for sealing the kit, recording start/end times, and mailing it promptly to avoid delays that can affect lab analysis. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Step 7: Record results and decide next steps
When your result arrives, compare it to EPA guidance. If high, plan for confirmatory testing (if needed) and mitigation. If low, plan future retesting at a reasonable interval or after changes to the home. EPA provides decision logic in its radon guidance. (Source: EPA – https://www.epa.gov/radon)
6) Where to place the test (the #1 place people mess up)
Placement is the biggest quality variable in DIY radon testing. Even a good kit can give a misleading result if it’s placed in a location that doesn’t represent normal breathing air.
The golden rule: test the lowest lived-in level
If you spend time in the basement (finished basement, office, bedroom, gym), test there. If the basement is unfinished and you never go down there, you can test the lowest level you actually live in—but many homeowners still test the basement to understand the home’s radon “source level,” especially if the basement may be used later. EPA’s guidance centers on the lowest lived-in level. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Where NOT to place a radon test
- Right next to a window or exterior door
- Directly under an HVAC supply vent or return
- Bathrooms, kitchens, laundry rooms (high humidity and unusual airflow)
- Near fireplaces or wood stoves
- In direct sunlight or near heat sources
These locations can distort readings due to drafts, humidity, or non-representative air mixing. EPA’s general testing instructions emphasize avoiding drafts and unusual airflow zones. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
7) Closed-house conditions: what they are and when they matter
“Closed-house conditions” are most commonly referenced for short-term tests, especially during real estate transactions. The idea is to run the test under conditions that reflect typical closed-up living—so the result doesn’t get artificially lowered by wide-open windows and unusual ventilation. (Source: EPA home buying radon guidance PDF – https://www.epa.gov/system/files/documents/2024-11/2024-buying-a-new-home-how-to-protect-your-family-from-radon_0.pdf)
EPA guidance commonly describes keeping windows closed and limiting the opening of exterior doors to normal entry/exit during the test, with closed-house conditions started before the test begins (often at least 12 hours, depending on protocol and context). (Source: EPA home buying radon guidance PDF – https://www.epa.gov/system/files/documents/2024-11/2024-buying-a-new-home-how-to-protect-your-family-from-radon_0.pdf)
For long-term tests: closed-house conditions matter less, because the test averages over normal living behavior across seasons. The bigger goal is simply “normal living,” not a specific closed-house snapshot. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
8) Common mistakes that can ruin a radon test
Most “bad radon tests” don’t happen because the kit is defective. They happen because the test environment wasn’t controlled well enough to reflect normal indoor air.
Top mistakes to avoid
- Placing the kit in a drafty location (window sill, near doors, near vents)
- Running the test in a bathroom or kitchen (humidity, fans, rapid air changes)
- Moving the kit during the test (changes the exposure environment)
- Not following the time window (ending early or forgetting to start promptly)
- Opening windows constantly during a short-term test (artificially lowers indoor radon)
- Delaying shipment for charcoal kits (lab analysis depends on timing)
EPA’s guidance documents emphasize following device instructions and avoiding drafts and unusual airflow patterns to get reliable results. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
9) How to interpret your results
Interpreting radon results is straightforward once you understand two things: radon varies, and decisions depend on both the number and the test type.
If your result is below 2.0 pCi/L
This is generally considered a “low” result in the sense that it’s below the level where EPA suggests considering action. But “low” does not mean “zero risk,” because EPA states there is no known safe level. The main next step is to plan retesting over time and after significant home changes. (Source: EPA action level – https://www.epa.gov/radon/what-epas-action-level-radon-and-what-does-it-mean)
If your result is between 2.0 and 4.0 pCi/L
EPA encourages homeowners to consider mitigation in this range. Many homes can be reduced below 2.0 pCi/L with common mitigation techniques. If your number is near 4.0 and the test was short-term, a follow-up test can help you understand your typical level before making decisions. (Source: EPA action level – https://www.epa.gov/radon/what-epas-action-level-radon-and-what-does-it-mean)
If your result is 4.0 pCi/L or higher
EPA recommends fixing your home at or above 4.0 pCi/L. If the result came from a short-term test, EPA guidance often involves confirming with a second short-term test or moving to a long-term test (if time allows) depending on the situation. (Source: EPA Citizen’s Guide PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
If your result is very high (example: 20 pCi/L or more)
EPA materials discuss that high readings warrant faster action. In practical terms, the higher the number, the more urgent it is to confirm and mitigate. If you get an unusually high short-term result, consider running a second short-term test immediately (following instructions closely) and contacting a qualified radon mitigation professional. (Source: EPA – https://www.epa.gov/radon)
10) What to do if your radon is high (next steps)
If your radon level is elevated, don’t panic. Radon is common, and mitigation is a mature, well-understood home improvement.
Step 1: Confirm (if needed)
If you used a short-term test and got a result near a decision boundary, confirm with a follow-up test per EPA guidance. If you used a long-term test, you already have a stronger estimate of your annual average. (Source: EPA Citizen’s Guide PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Step 2: Understand the most common mitigation approach
The most common mitigation method is sub-slab depressurization (or related soil suction methods), which uses a vent pipe and fan to draw radon from beneath the home and vent it safely above the roofline. EPA explains that mitigation can reduce radon in most homes with today’s technology and provides consumer guidance on radon reduction approaches. (Source: EPA Consumer’s Guide to Radon Reduction PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
Step 3: Test again after mitigation
Post-mitigation testing is essential. A mitigation system should be verified with a test to confirm that radon levels dropped as intended. (Source: EPA – https://www.epa.gov/radon)
11) Retesting: how often to test and when to re-test
Even after you have a result, radon testing isn’t necessarily “one and done.” Homes change, HVAC patterns change, seasons change, and mitigation fans eventually wear out. EPA provides retesting guidance and encourages retesting after major changes. (Source: EPA – https://www.epa.gov/radon/how-often-should-i-testretest-my-home-radon)
Retest if:
- You install a radon mitigation system (to confirm performance)
- You remodel or finish a basement
- You change HVAC systems or make major ventilation changes
- You do foundation repairs that could open/close soil gas pathways
- You haven’t tested in several years and want an updated baseline
12) Testing in special situations (crawlspaces, apartments, new homes, schools)
Crawlspaces
Crawlspaces can be radon entry pathways because they often have exposed soil or venting patterns that change seasonally. Testing should still focus on the lowest lived-in level above the crawlspace, following standard placement rules. If a crawlspace is part of a real estate or diagnostic process, a professional may use specific protocols. (Source: EPA “A Citizen’s Guide to Radon” PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Apartments and multi-unit buildings
Radon risk is often higher on lower levels (garden units, first-floor units over basements), but building design and air movement can distribute radon in complex ways. If you rent, you may need to coordinate with building management about testing and mitigation. (Source: EPA – https://www.epa.gov/radon)
New homes
New construction can have elevated radon just like older homes. Radon potential depends on the site and the building’s interaction with soil gas—not the age of the home. EPA discusses radon-resistant construction approaches and still recommends testing. (Source: EPA – https://www.epa.gov/radon/radon-resistant-construction-basics-and-techniques)
Schools and workplaces
EPA recommends testing schools for radon and provides guidance specific to school environments. These are high-occupancy buildings, and testing is a practical prevention step. (Source: EPA – https://www.epa.gov/radon/radon-schools)
13) Radon testing during real estate transactions
Real estate radon testing often uses short-term tests because of timeline constraints. The goal is to run the test under controlled conditions that represent normal closed-house living (to avoid artificially low results). EPA provides a home-buying radon guidance document that discusses testing and protection strategies. (Source: EPA home buying guidance PDF – https://www.epa.gov/system/files/documents/2024-11/2024-buying-a-new-home-how-to-protect-your-family-from-radon_0.pdf)
If a test comes back high during a transaction, the most common resolution is either mitigation before closing, a credit/escrow, or another negotiated solution. From a science standpoint, the key is to ensure the test followed appropriate placement and condition protocols so the result is meaningful. (Source: EPA – https://www.epa.gov/radon)
14) Professional testing vs DIY: what’s the difference?
DIY testing can be excellent if you follow instructions carefully. The advantages are cost and convenience. The main risks are placement errors and poor control of test conditions.
Professional testing may involve calibrated continuous monitors, adherence to formal protocols, and chain-of-custody reporting—particularly useful for real estate, workplace, or compliance settings. If you suspect unusual airflow patterns, have a complex foundation, or want maximum confidence quickly, professional testing can be worthwhile. (Source: EPA – https://www.epa.gov/radon)
Practical approach: Many homeowners do an initial DIY test. If the result is elevated, they either do a confirmatory DIY test or call a professional depending on urgency and confidence needs. EPA’s decision guidance supports confirmatory testing logic based on results and test type. (Source: EPA Citizen’s Guide PDF – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Sources and further reading
- EPA Radon Hub: https://www.epa.gov/radon
- EPA – What is the EPA action level? https://www.epa.gov/radon/what-epas-action-level-radon-and-what-does-it-mean
- EPA – A Citizen’s Guide to Radon (PDF): https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf
- EPA – Consumer’s Guide to Radon Reduction (PDF): https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf
- EPA – How often should I test/retest? https://www.epa.gov/radon/how-often-should-i-testretest-my-home-radon
- EPA – Radon in schools: https://www.epa.gov/radon/radon-schools
- EPA – Radon-resistant construction: https://www.epa.gov/radon/radon-resistant-construction-basics-and-techniques
- CDC – Radon overview: https://www.cdc.gov/radon/about/index.html
- EPA – Home buying and radon (PDF): https://www.epa.gov/system/files/documents/2024-11/2024-buying-a-new-home-how-to-protect-your-family-from-radon_0.pdf
Bottom line
If you take only one thing from this article, take this: testing is the only way to know. Once you have a number, you can make a rational decision—confirm if needed, mitigate if recommended, and retest over time. Radon isn’t something you guess. It’s something you measure. (Source: EPA – https://www.epa.gov/radon)