Short answer
Yes, a radon test from a qualified laboratory gives a reliable reading when it is used as its instructions say. Most wrong results come from how the test was run, not the device: improper testing may give an inaccurate result, and one short test only captures a few days of a level that changes.
Next step: pick the right test for your home. Which test to use
Reliable devices are sold in hardware stores and by mail, and qualified testers use them too. What makes the number trustworthy is a qualified laboratory,
Results close to the
What to do next: use a device from a qualified laboratory, follow the testing checklist, and confirm any high short-term result with a second test.
At a glance · 1 min read
Radon cannot be seen or smelled, so a device has to measure it, and reliable devices are easy to find: from qualified testers and companies, by phone or mail order, and in hardware stores and other retail outlets. Whether the number is right depends less on the device than on two other things: the laboratory behind it, and how the test was run.
| Factor | What it takes |
|---|---|
| The laboratory | A device from a qualified laboratory, used as its instructions say |
| Test length | At least 48 hours; some devices need longer |
| Closed house | Windows and outside doors shut from at least 12 hours before a 2 to 4 day test, and for the whole test |
| Placement | The lowest level that could be used regularly, at least 20 inches above the floor, away from drafts, high heat, high humidity and exterior walls |
| Rooms to avoid | Kitchens, bathrooms, laundry rooms, furnace rooms, closets, stairways, hallways and crawl spaces |
| Hands off | The device is not disturbed at any time during the test |
| After the test | The device goes back to the laboratory promptly, with the start and stop times and the location filled in |
Skip one of these and the reading can be off: improper testing may give an inaccurate result and mean another test. If a seller or tester cannot confirm every item was done, the answer is another test.
At a glance · 1 min read
Radon devices come in two families. Passive devices need no power: they sit in the home for a set time and are then sent to a laboratory for analysis. Active devices need power and record the level as they go, usually hourly, with an average for the test period.
| Aspect | Passive devices | Active devices |
|---|---|---|
| Examples | Charcoal canisters, alpha-track detectors, charcoal liquid scintillation devices, electret ion chamber detectors | Continuous radon monitors and continuous working level monitors |
| Power | None | Needed |
| Result | From the laboratory after the device is mailed back | A record over time, usually hourly readings and an average |
| Cost | Generally inexpensive, short-term and long-term | May cost more |
| Interference | Some types resist disturbance better than others | The record can reveal unusual swings; some models deter and detect interference |
| Test | How long it runs | What it is for |
|---|---|---|
| Short-term test | Stays in the home from 2 to 90 days, depending on the device, and for a minimum of 48 hours. | A faster screening result. Because radon levels vary from day to day and season to season, it is less likely than a long-term test to tell you the year-round average. |
| Long-term test | Stays in the home for more than 90 days. | It is more likely than a short-term test to tell you the home's year-round average radon level. |
| Continuous monitor | Logs readings for the whole test, run as a short-term or a long-term test under the same durations in EPA guidance. | Logs a graph over time, so you can see trends and spot anomalies rather than a single number. |
Neither family is the accurate one and the other the rough one. The active devices with anti-interference features may give a more reliable result where interference is a risk, as in a home sale. Devices keep changing, so a state radon office can tell you which suit your needs before you test.
At a glance · 1 min read
Even a perfect device only measures the days it was in the house. Radon varies within a building from day to day and even hour to hour, and from season to season, so a
| Approach | What it improves |
|---|---|
| Two tests at the same time, side by side | The precision of the measurement |
| One test followed by another | A better picture of the seasonal average |
| A long-term test, more than 90 days | The best picture of the year-round level |
At a glance · 1 min read
Most wrong results trace back to the test, not the detector. Opening up the house is the big one: fresh air dilutes the radon while windows are open, and levels most often return within about 12 hours of closing up, so a test run with windows open reads low.
| Error | Effect on the reading |
|---|---|
| Windows or outside doors left open | Outdoor air dilutes the radon, so the result is likely too low |
| Fans that bring in outside air running | The same dilution; only a radon system's fan and small exhaust fans for short periods may run |
| Testing in a kitchen, bathroom or other humid or drafty room | Outside the places the guidance allows for a test device |
| Moving or disturbing the device | Can invalidate the result, and is illegal in some states |
| A short test during a severe storm or high winds | Short-term tests of under four days are not run in that weather |
| Mailing the device back late | The laboratory needs it promptly, with times and location recorded |
Professional testers in a sale guard against interference by recording barometric pressure and temperature during the test. Deliberate tampering is covered in how a radon test can be manipulated, and everyday influences in what can affect a radon test.
At a glance · 1 min read
Accuracy also rests on consistency. Measurements need to follow national protocols so they are consistent and reliable enough to make decisions on, and short-term tests done that way are useful when time is short, as in a home sale. Residential radon can be measured simply and cheaply with small passive detectors.
| Check | Why it matters |
|---|---|
| A device from a qualified laboratory | Passive devices are analyzed by the laboratory, so its quality counts |
| A list from your state | Your state may list do-it-yourself devices from qualified laboratories |
| A tester's state license or credential | Many states license radon professionals; elsewhere, ask for a proficiency credential |
| A seller's earlier result | A buyer may ask for a new test if the checklist was not met, the test is more than about two years old, or the home was renovated since |
Questions · 1 min read
Yes, when the kit comes from a qualified laboratory and the test follows its instructions and the closed-house rules. Most bad results come from how the test was run. See can I test for radon myself.
They are active devices that measure and record the level as they run, which can reveal unusual swings during the test. Like any device, they need the full test conditions and at least 48 hours.
Radon varies from day to day and season to season, so two tests on different days measure different air. Running two tests side by side at the same time is what improves precision.
Yes, if the test is done improperly: open windows, a bad location or a disturbed device can give an inaccurate result. If the checklist was not met, take another test.
It is right at the line, where a short-term result is least certain: there is about a 50 percent chance the year-round average is somewhat below or above 4 pCi/L. See is a radon level of 4.1 considered high.
Check it against the testing checklist. A buyer may ask for a new test if the checklist was not met, if the test is not recent, within about two years, or if the home has been renovated since.
How a radon test works, who can run one, and how to read the number it gives you.
How a professional radon test works, what it proves and whether it is worth it.
Read the guideWhat counts as high and how to bring them down.
Read the guideEPA's action level, WHO's reference level and what counts as acceptable.
Read the guide