Test for Radon: What Homeowners Need to Know
Radon is invisible and odorless, so the only way to know whether a home has a problem is to measure it directly. Learning how to test for radon — what kits exist, where to place them, and how to read results — lets any homeowner take a meaningful step toward safer indoor air for a modest cost. This guide summarizes EPA and Colorado state health guidance current as of 2026 and is informational only; consult a physician about health concerns and a certified professional for testing or mitigation decisions.
How do you test for radon?
You test for radon using either a do-it-yourself test kit or a professional measurement service. DIY kits are inexpensive, widely available, and accurate when used correctly: you place the device in the lowest occupied level of the home, leave it for the specified period, and send it to a lab or read it electronically. Professional testing uses calibrated continuous monitors and is common during real estate transactions.
Both approaches measure radon concentration in picocuries per liter (pCi/L). The EPA recommends testing every home, and the test is the foundation of every later decision. For local context, our guide to radon testing in Colorado explains why Front Range homes are strong candidates for testing.
Short-term versus long-term tests
The two main test durations answer slightly different questions.
Short-term tests
Short-term tests run from two to about ninety days and give a quick snapshot. They are ideal when speed matters — for example, during a home purchase. Because radon fluctuates with weather and season, a short test is a screening tool rather than a definitive annual figure.
Long-term tests
Long-term tests run more than ninety days and capture seasonal variation, producing a more representative average of year-round exposure. They take patience but give the truest picture of what a household actually breathes.
A common strategy is to start with a short-term test and, if the result is borderline or elevated, follow with a long-term test or a second short-term test to confirm. Our explainer on how often you should test for radon covers retesting timing.
How much does radon testing cost?
Radon testing is one of the most affordable home-safety steps available. Passive DIY kits — charcoal canisters and alpha-track detectors — typically cost a modest amount including the lab analysis fee, and some state programs offer them at reduced cost to encourage testing. Continuous electronic monitors cost more up front but provide ongoing readings without recurring lab fees.
Professional testing, common during real estate transactions, costs more than a DIY kit because it includes a calibrated continuous monitor, the inspector’s time, and a documented, tamper-resistant result. Even so, the expense is small relative to a home purchase or the value of the protection it provides. Given how inexpensive testing is against the seriousness of the risk, cost is rarely a good reason to skip it. For Front Range homeowners over Colorado’s radon-rich geology, the modest price buys meaningful peace of mind.
Types of radon test devices
Several device types are available, each with trade-offs.
Charcoal canisters and alpha-track detectors
These passive devices are placed for the test period and mailed to a lab for analysis. Charcoal canisters suit short-term testing; alpha-track detectors suit longer durations. Both are affordable.
Electronic and continuous radon monitors
Digital monitors display readings continuously and can track trends over time. They cost more up front but offer ongoing visibility. Homeowners can read about these in our overview of electronic radon detectors.
For a one-time check, a passive lab kit is economical. For ongoing monitoring, a continuous monitor adds peace of mind.
Where and how to place the test
Placement determines accuracy. Put the device in the lowest level of the home that is regularly occupied — a basement living area, or the lowest floor if the basement is unused. Place it away from drafts, exterior walls, windows, and high humidity, at a height of roughly two to six feet, on a surface where it will not be disturbed.
Maintain closed-house conditions during a short-term test: keep windows and exterior doors shut except for normal entry and exit, and avoid running whole-house fans that bring in outside air. Following the kit’s instructions precisely is what makes the reading trustworthy. Closed-house conditions should generally begin twelve hours before the test starts and continue throughout, so the measurement reflects how radon accumulates in normal lived-in conditions rather than a temporarily ventilated home. Normal use of the heating or air-conditioning system is fine; it is fresh-air ventilation that skews a short-term result low.
Reading your results
Results come back in pCi/L. The EPA action level is 4.0 pCi/L: at or above that, mitigation is recommended. Between 2 and 4 pCi/L, the EPA suggests considering mitigation, since no level is entirely without risk. Below 2 pCi/L, levels are relatively low, though periodic retesting is still wise.
A single short-term result above the action level warrants confirmation before spending on mitigation, ideally with a follow-up test. Levels also vary seasonally, so a winter reading may differ from a summer one. Our guide on what radon level is dangerous puts the numbers in context.
Testing during a home purchase
Radon testing is common during real estate transactions, and in high-radon areas like the Front Range, buyers frequently request it. Because transactions move fast, a short-term professional test with a continuous monitor is typical. Buyers should ensure the test follows closed-house conditions and that the testing party is independent where possible.
A high result during a purchase is not a deal-breaker — mitigation is effective and often negotiated into the sale. Knowing the level before closing simply gives the buyer information and leverage.
Common testing mistakes to avoid
Most inaccurate radon results come from preventable errors. Placing the device in the wrong spot — near a window, in a draft, in a bathroom, or in an unoccupied attic — skews the reading. Failing to maintain closed-house conditions during a short-term test lets outside air dilute the result and understate the true level. Disturbing or moving the device mid-test invalidates it.
Other frequent mistakes include testing during unusual weather such as a major storm, which can temporarily spike levels, and ignoring the kit’s expiration date or mailing deadline, since charcoal canisters lose accuracy if analyzed too late. Reading the instructions carefully and following them exactly is the single best way to get a result you can trust. When in doubt, a continuous monitor or a professional test removes much of the room for error.
DIY kits versus professional testing
For a homeowner simply checking their own residence, an inexpensive DIY kit from a hardware store or state health program is accurate when used correctly and is the right starting point. The Colorado health department periodically offers low-cost or discounted kits to encourage testing, which Front Range residents can take advantage of.
Professional testing makes more sense in specific situations: during a real estate transaction where an independent, tamper-resistant result matters, when confirming an elevated DIY reading before paying for mitigation, or when a continuous monitor’s detailed data is wanted. Professionals use calibrated continuous radon monitors and follow protocols that resist tampering, which is why they are standard in home sales. The choice comes down to purpose — personal awareness favors a DIY kit, while a transaction or a mitigation decision favors a professional measurement.
What to do after testing
If results sit below the action level, retest periodically, after major renovations, and if living patterns change (such as finishing a basement). If results meet or exceed 4.0 pCi/L, the next step is mitigation by a qualified contractor. Sub-slab depressurization, the standard system, reliably lowers levels. Our overview of how radon mitigation works explains the proven approach.
Testing is the inexpensive first step that makes every later decision informed. Given Colorado’s elevated radon profile, Front Range homeowners have strong reason to test now rather than wait.
How often to retest
A single test is a starting point, not a permanent answer, because radon levels can change over time. The EPA recommends retesting periodically — generally every few years — and at specific trigger points. A home should be retested after major renovations that alter the foundation or air flow, after finishing a basement, after installing or servicing a heating or ventilation system, and after any structural changes that could open new entry paths.
Homes with a mitigation system installed should be retested after installation to confirm it worked, and periodically afterward to verify it keeps working. Seasonal variation also argues for repeat testing; a home that tested low in summer may read higher in winter. Treating radon testing as an occasional habit rather than a one-time event keeps a household’s information current. Our guide on how often to test for radon covers these intervals in more depth.
Interpreting borderline results
Results near the action level can leave homeowners unsure how to respond. A reading right at or just below 4.0 pCi/L deserves a confirmation test before any decision, since short-term readings fluctuate with weather and season. Two short-term tests, or a longer-term test, give a more reliable picture than a single snapshot.
The EPA notes that risk exists below 4.0 pCi/L too, and suggests considering mitigation between 2 and 4 pCi/L, especially for households with long occupancy or members at higher risk. Below 2 pCi/L, levels are relatively low, though periodic retesting remains sensible. The action level is a guideline for when mitigation is clearly recommended, not a sharp line between safe and dangerous. Confirming a borderline result and weighing personal circumstances leads to a sounder decision than reacting to one number.
References
- How to Test Your Home for Radon — U.S. Environmental Protection Agency
- Test Your Home for Radon — Colorado Department of Public Health and Environment
- Radon Testing and Lung Health — American Lung Association
If you would like help testing your Front Range home or interpreting a radon reading before a purchase, you can get in touch with a vetted local inspector through our contact page. A reliable test is the first step toward cleaner indoor air.