Radon Test Results: How to Read Them and What to Do
A radon test comes back as a single number, and that number drives a real decision about your home. Reading radon test results correctly means understanding the unit, the action thresholds, and the difference between a snapshot and a true average. This guide summarizes EPA and Colorado state guidance current as of 2026; consult a certified radon professional for decisions about your specific home. The goal here is to make the report make sense so the next step is obvious rather than confusing.
How to read your radon test results
Radon results are reported in picocuries per liter of air, written pCi/L. The single number is the average concentration measured over the test period. The EPA uses 4.0 pCi/L as the action level: at or above it, mitigation is recommended. Between 2 and 4 pCi/L, the EPA suggests considering action, because risk does not drop to zero below 4. Below 2 pCi/L is generally considered low, though no level is entirely risk-free.
Context helps the number land. The average outdoor level is about 0.4 pCi/L and the national indoor average is roughly 1.3 pCi/L. A Front Range basement reading of 6 or 8 pCi/L is high but not unusual for Colorado, given the region’s uranium-rich soils. The wider framework sits in the Colorado radon testing guide, and homeowners trying to gauge a basement-specific number can compare against safe radon levels in a basement.
Short-term versus long-term results
The kind of test shapes how much weight to give the result. The two formats answer slightly different questions.
Short-term test results
A short-term test runs two to seven days and gives a quick snapshot. It is the standard during a real-estate transaction because of the timeline. The trade-off is that radon swings with weather, season, and how the home is operated, so a single short-term result can run high or low compared to the year-round average. A storm or a closed-up cold snap can skew it.
Long-term test results
A long-term test runs more than 90 days and reflects the true average more reliably. For a homeowner deciding about their own residence rather than meeting a closing deadline, a long-term test gives the most trustworthy picture. In Colorado, where winter sealing pushes levels up, a long-term or repeated test is especially valuable.
What to do after a high or borderline result
The right response depends on the number and the test type. A result at or above 4.0 pCi/L from a short-term test should be confirmed, because mitigation is a significant step and you want certainty. Confirm with a long-term test or a second short-term test before committing. A result clearly in the high single digits or teens is consistent enough that proceeding to mitigation is reasonable.
A borderline result between 2 and 4 pCi/L is a judgment call. The EPA’s “consider action” framing means weighing the cost of mitigation against the modest but real risk reduction. Many Front Range homeowners choose to mitigate in this range given Colorado’s overall radon prevalence. Whatever the decision, the Colorado Department of Public Health and Environment recommends re-testing every few years and after major renovations, because levels can change. Homeowners moving toward a fix can review the guide on how to mitigate radon.
Reading a professional lab report
A lab-analyzed result, whether from a charcoal canister or an alpha-track detector, arrives as a report with more than just the headline number. Knowing how to read the supporting details helps you judge its reliability.
The key fields
Look for the test start and end dates, which confirm the exposure duration and tell you whether the protocol was followed; a short-term charcoal test left out too long or too briefly can skew the result. The report states the measured concentration in pCi/L, and many include the device serial number and the lab’s certification. A reputable report also notes the placement location and any closed-house conditions, which matter for interpreting whether the test reflected realistic living conditions.
Continuous monitor reports
A continuous radon monitor produces a richer report, often graphing hour-by-hour fluctuations alongside the average. This detail reveals whether the level was steady or spiked, and it can flag tampering, such as a window opened mid-test, which shows as a sudden drop. For a homeowner, the average still drives the decision, but the graph adds confidence that the number is genuine rather than an artifact of weather or interference.
How Colorado conditions shape your reading
A Front Range result should be read with the local context in mind. Because Colorado’s geology generates abundant radon and its cold winters keep homes sealed, a reading that might look surprisingly high elsewhere is unremarkable here. A basement testing at 5, 8, or even into the low teens of pCi/L is a routine finding across Denver-metro and foothill counties, not an anomaly.
This regional baseline cuts two ways. It means a homeowner should not panic at a high number, since it is common and fixable, but it also means a low summer reading should not breed complacency, because the winter level in the same home may be considerably higher. The seasonal swing is large enough in Colorado that public health guidance leans toward longer-term testing or winter testing for a representative picture. Buyers comparing a transaction-driven short-term result against the home’s likely year-round reality benefit from understanding this seasonal gap rather than treating one number as the whole story.
Why results change and when to re-test
Radon is not static. The same home can produce different results across seasons because temperature, barometric pressure, soil moisture, and how the home is ventilated all influence how much soil gas enters. A summer test with windows open will often read lower than a sealed-up winter test. This variability is exactly why confirmation matters before acting on a single short-term number.
Re-testing is recommended every two years, after installing or servicing a mitigation system to verify it worked, and after major structural changes such as a foundation repair or a finished basement. The American Lung Association stresses that ongoing awareness, not a single test, is what keeps a household protected. A result is a moment in time; smart radon management treats it as the start of a habit rather than a one-time verdict.
Comparing results across tests
Homeowners sometimes accumulate several radon results over time, from a transaction test, a follow-up, and periodic re-tests, and reconciling them can be confusing. The key is to recognize that each number reflects the conditions during its specific window, so differences between tests usually signal changing conditions rather than a faulty test. A summer short-term result of 2 pCi/L and a winter long-term result of 5 pCi/L in the same home are not contradictory; they capture the seasonal swing that Colorado homes routinely show.
When results disagree, weight them by reliability. A long-term test that spans a heating season carries more weight for understanding the home’s true average than a single short-term test taken in mild weather. A continuous monitor’s averaged result, backed by its hour-by-hour graph, is also high-confidence. If a transaction short-term test came back borderline and a later long-term test reads clearly elevated, the long-term result is the better basis for deciding on mitigation. Rather than treating conflicting numbers as a problem, a homeowner can read the pattern across tests as a fuller portrait of how radon behaves in the home through the year.
From result to decision: a practical framework
A radon result is only useful if it leads to a clear decision, and a simple framework keeps the choice grounded. A confirmed average at or above 4.0 pCi/L points to mitigation; the EPA recommends fixing the home, and the proven active soil depressurization system reliably brings levels down. A result clearly in the high single digits or teens is consistent enough that proceeding to mitigation is reasonable, while a single high short-term spike warrants a confirming test first.
A borderline result between 2 and 4 pCi/L is the judgment zone. The EPA’s “consider action” guidance means weighing the modest cost of mitigation against a real but smaller risk reduction. Many Front Range homeowners choose to mitigate in this range given Colorado’s overall radon prevalence and the affordability of a system. Below 2 pCi/L, the level is generally considered low, though periodic re-testing remains wise because no level is entirely risk-free and conditions change. Homeowners moving toward a fix can review the practical steps in the guide on how to mitigate radon, which connects a result to the work that lowers it.
Acting on results to protect your household
The ultimate purpose of a radon test is protecting the people who live in the home, and the result matters only insofar as it drives that protection. A high reading left in a drawer does nothing; the same reading acted upon, through confirmation and then mitigation, removes a leading environmental cause of lung cancer from the household’s exposure. Because the risk is cumulative over years, the sooner an elevated level is addressed, the more total exposure is avoided.
For Colorado families, where elevated results are common, building radon awareness into homeownership pays off. Test when buying, re-test every couple of years and after major renovations, verify any mitigation system with a post-installation test, and treat the numbers as ongoing information rather than a one-time verdict. The American Lung Association emphasizes that this habit of testing and acting, not a single measurement, is what genuinely keeps a household safe. A radon result is the start of that protection, and reading it correctly is the first step toward acting on it well.
Radon results in a real-estate transaction
Test results carry particular weight during a home sale, and Colorado buyers and sellers should know how they function. Because the inspection contingency runs on a tight clock, transaction testing is almost always a short-term test, often a two-to-seven-day measurement under closed-house conditions. The resulting number becomes a negotiation point: a result at or above the action level commonly leads a buyer to request that the seller install a mitigation system before closing, provide a credit toward one, or adjust the price.
Sellers benefit from understanding that a documented mitigation system, verified by a post-installation test, reassures buyers and can smooth the sale rather than triggering last-minute renegotiation. Buyers should ask whether a home already has a system and request its test history, since a verified low result after mitigation is exactly the outcome they want. In a region where elevated readings are routine, treating radon results as an expected part of the transaction, rather than a surprise, keeps both parties calm and focused on the straightforward fix that an elevated result calls for.
Keeping a record of your radon results
Radon results are most useful when retained and compared over time, so keeping a simple record pays off. Save each test report with its dates, location, and measured level, whether from a charcoal kit, an alpha-track detector, or a continuous monitor. Over years, this record reveals how the home’s radon behaves across seasons and after changes such as a basement finish, a foundation repair, or a new furnace.
The record also supports decisions and disclosures. A homeowner who later sells can document a verified low level or a mitigation system’s performance, and one who mitigates can prove the before-and-after reduction. For families focused on long-term health, the record confirms that cumulative exposure has been kept low through consistent testing and any needed action. Because radon levels shift with conditions and home modifications, treating results as an ongoing log rather than isolated snapshots gives the truest picture. Pairing that record-keeping with regular re-testing, every couple of years and after major changes, is the habit that keeps a household genuinely protected against the slow, cumulative risk radon presents over time.
References
- A Citizen’s Guide to Radon — EPA
- Radon in Colorado — Colorado Department of Public Health and Environment
- Radon and Lung Health — American Lung Association
If your radon test results came back high or borderline, contact us here to connect with a certified Front Range radon professional for confirmation testing and mitigation.