Radon House Test: How to Test Your House for Radon
Testing a house for radon is one of the simplest, lowest-cost protective steps a homeowner can take, and yet it is the only way to detect a gas that causes thousands of lung cancer deaths a year. A radon house test puts a number on the invisible: how much radon is accumulating in the air people breathe at home. The process is approachable enough for any homeowner to do with a kit, and exact enough to drive a real mitigation decision when the result is high. This guide walks through the kit types, placement, duration, interpreting the result, and when to act. It summarizes EPA and Colorado state guidance current as of 2026; consult a certified radon professional for testing decisions and your physician for any health concerns.
How do you test your house for radon?
You test by placing a radon measurement device in the lowest livable level of the home, leaving it undisturbed for the prescribed time under controlled conditions, then either reading the device or sending it to a lab for analysis. The result comes back in picocuries per liter (pCi/L), the standard radon unit, and that number tells you whether action is needed.
Two paths exist: a do-it-yourself kit or a professional measurement. DIY kits are inexpensive and reliable when used correctly, while professional testing adds calibrated equipment and a documented report that carries weight during a home sale. Colorado’s Front Range has high radon prevalence, so testing is a sensible default for any home in the region, a point the broader radon testing resources develop in detail.
Kit types: which one to use
Several device types serve different needs, and choosing the right one starts with how quickly and how definitively you need an answer.
Charcoal canister (short-term)
Activated charcoal canisters absorb radon over a 2-to-7-day exposure, then go to a lab that measures the captured radon. They are inexpensive, widely sold, and good for a quick first screen. Because they are sensitive to humidity and only capture a short window, they give a snapshot rather than a yearly average.
Alpha-track detector (long-term)
Alpha-track detectors record radon over more than 90 days, producing a result closer to the home’s year-round average. Because radon fluctuates with weather and season, this long-term reading is more representative of true exposure, which is why the EPA recommends it for a definitive assessment.
Electronic continuous radon monitor
Continuous monitors are digital devices that log radon hourly and display a running result. Some are consumer models that stay in the home indefinitely; professional-grade monitors used in real estate transactions are calibrated and tamper-resistant. They give the richest data and the fastest feedback. The various DIY options are compared in the guide to the at-home radon test.
Where to place the test device
Placement strongly affects accuracy. Put the device in the lowest level of the home that is or could be regularly occupied, typically a basement or a ground-floor living space, since that is where radon enters first and concentrates. Set it at breathing height, roughly 2 to 6 feet off the floor, on a table or shelf.
Keep the device at least a few feet from exterior walls, windows, and doors, and away from drafts, heat sources, and high-humidity areas like bathrooms or near a sump pump. Do not place it in a kitchen or laundry where moisture and air movement skew results. Avoid disturbing or moving the device during the test. Proper placement is the difference between a result you can trust and one that misleads, and it applies whether you use a DIY kit or hire a pro, as the radon measurement guide reinforces.
How long to test and under what conditions
Duration depends on the device. Short-term charcoal tests run 2 to 7 days, long-term alpha-track tests run more than 90 days, and continuous monitors can report after 48 hours and keep updating. For a first screen, a short-term test is the usual starting point; for a definitive read of an occupied home, a long-term test is preferred.
Closed-house conditions are essential for short-term testing. Keep windows and exterior doors shut except for normal entry and exit, beginning at least 12 hours before the test starts and continuing throughout. Run heating and air conditioning normally, but avoid whole-house fans or window fans that move outside air through the home. These conditions ensure the test measures radon as it would actually accumulate, not a diluted reading from open windows.
Interpreting your pCi/L result
The result arrives in picocuries per liter. The EPA recommends taking action to reduce radon at 4.0 pCi/L or higher and suggests considering action between 2.0 and 4.0 pCi/L, since no level is entirely without risk. Outdoor air averages about 0.4 pCi/L, so the practical goal of any fix is to get indoor levels as close to outdoor levels as feasible.
A single short-term result is a snapshot of a fluctuating quantity. If a short-term test comes back near or above 4.0, the EPA advises confirming it with a second short-term test or a long-term test before committing to mitigation. A clearly high reading, such as 8 or 10 pCi/L, is strong enough that mitigation is warranted without much hesitation. Reading the number against these benchmarks, rather than reacting to a single figure in isolation, leads to sound decisions.
When to mitigate after testing
Mitigation is warranted when a confirmed result reaches 4.0 pCi/L or higher, and worth considering between 2.0 and 4.0. The standard solution is an active soil depressurization system that draws radon from beneath the foundation and vents it above the roof, explained in the guide to how to mitigate radon. A certified installer designs the system to the home, and a post-mitigation test confirms it worked.
Even after mitigation, periodic retesting matters, since fans can fail and conditions change. The EPA suggests retesting every couple of years and after any major renovation. For a home that tests low, retesting every few years still makes sense, because changes to the foundation or surrounding soil can shift levels over time. Testing is not a one-time event but a periodic habit that keeps a household informed.
Common mistakes that ruin a result
Most invalid radon tests come from a handful of avoidable errors, and knowing them is half the battle. The frequent one is breaking closed-house conditions, opening windows for fresh air, running a whole-house fan, or leaving a door propped during the test, all of which dilute the reading and can hide a genuine problem. Another is poor placement: setting the device on the floor, against an exterior wall, in a draft from a supply register, or in a humid bathroom or laundry, any of which skews the number.
Disturbing the device mid-test is a third pitfall; moving it, covering it, or relocating it partway invalidates the measurement. With charcoal canisters, delay matters, because the device keeps absorbing and then off-gassing radon, so mailing it to the lab promptly after the exposure window is part of doing the test right. Testing during a major storm or extreme wind can also distort short-term results, since rapid pressure changes alter how soil gas enters. Following the device instructions exactly, and resisting the urge to “help” the test along, is what separates a number you can act on from one that misleads.
Confirming a result and choosing your next test
A single short-term test is a starting point, not a final answer, and the EPA’s own guidance builds in a confirmation step. When a short-term result lands near or above 4.0 pCi/L, the recommended move is a second test before committing to mitigation: either another short-term test for a fast answer or a long-term test for a more representative one. If both short-term tests agree, the case is settled; if they diverge, a long-term alpha-track test averaging over more than 90 days resolves which reading reflects reality.
The choice of follow-up depends on urgency. A buyer under a contract deadline does not have 90 days, so a second short-term test, ideally with a continuous monitor, gives a defensible answer inside the inspection window. An existing owner with no deadline can run a long-term test that captures seasonal swings, particularly valuable in a cold climate where winter readings tend to run higher than summer ones. Either way, two data points beat one, and a clearly high reading such as 8 or 10 pCi/L is convincing enough on its own that further delay only postpones a fix that is plainly warranted.
Front Range context: why testing is a default here
Colorado’s geology makes radon a routine concern rather than a remote possibility. Much of the state, including the Front Range counties of Denver, Boulder, Douglas, El Paso, and Jefferson, sits in the EPA’s highest-risk zone, where predicted average indoor levels exceed the action threshold, and the Colorado Department of Public Health and Environment reports that a large share of tested homes come back at or above 4.0 pCi/L. Uranium-bearing soils and rock, combined with the basement-and-slab construction common across the region, give radon both a source and a path indoors.
For a Front Range household, that prevalence flips the default: testing is the expected step, not an optional one, and a home that has never been tested is simply an unknown rather than a safe assumption. The same logic applies to a home with a mitigation system, which should be verified periodically to confirm it still performs. Whether testing for the first time or rechecking after a fix, the procedure described here, careful placement, closed-house conditions, and a confirming second test when results are borderline, is what produces a number a Colorado family can trust and act on. The broader radon testing resources place that habit in the wider context of protecting a home and its occupants.
DIY kit versus professional measurement: which to choose
The choice between a self-administered kit and a professional test comes down to purpose. For a homeowner simply checking a long-occupied home out of prudence, a quality DIY kit, charcoal for a quick screen or alpha-track for a year-round average, analyzed by a reputable lab is inexpensive and reliable when the placement and closed-house rules are followed. The cost is low, the process is approachable, and the result is perfectly adequate to decide whether mitigation is warranted.
Professional measurement earns its higher cost when the stakes or the scrutiny rise. During a real estate transaction, a calibrated continuous monitor placed by a trained professional produces a fast, tamper-resistant, documented result that holds up if it drives a negotiation, and it removes any question about whether the homeowner followed the protocol. Professional testing also helps when a homeowner is unsure about placement, wants a documented baseline before or after mitigation, or simply prefers an expert to handle it. Both paths measure the same gas against the same benchmarks; the kit suits routine self-checks, while the professional test suits transactions and decisions that others will rely on.
Building radon testing into a home maintenance routine
Testing is most valuable as a recurring habit rather than a single event, because radon is not a fixed property of a house. Soil shifts, foundations crack further with age, and changes to heating, ventilation, or the surrounding landscape can all move levels over time. The EPA’s guidance to retest every couple of years, and after any major renovation or foundation work, applies to homes that previously tested low as much as to those with a mitigation system to verify.
Folding radon into the same rhythm as other periodic home tasks, checking smoke and carbon-monoxide alarms, servicing the furnace, makes it routine rather than something remembered only at a sale. A homeowner with a mitigation system adds a glance at the manometer to confirm the fan still pulls suction, plus a periodic re-test. One who has never tested simply starts, since an untested home is an unknown rather than a safe one. Treating radon as an ongoing measurement, calibrated to a region’s risk, is what keeps a household informed across the years it occupies the home.
Front Range homeowners who want a professionally documented radon test, or help interpreting a result, can reach out through our contact page to connect with a vetted local provider.
References
- EPA citizen’s guide to radon testing — U.S. Environmental Protection Agency
- Colorado radon testing guidance — Colorado Department of Public Health and Environment
- Radon and lung health overview — American Lung Association