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Test every home for radon at least once: put a test kit in the lowest level people spend time in, three feet off the floor in the middle of the room, run it for the time on the package, and mail it to the lab. If the result is 4 pCi/L or higher, test again and, if it stays high, have a licensed professional install a mitigation system. That is the EPA's and the CDC's guidance, and the test costs less than a tank of gas.
Radon is a radioactive gas from the natural breakdown of uranium in soil and rock. It enters a house through the foundation and collects in the lowest levels. It has no smell or color, and the only way to know whether a home has a problem is to measure it.
What does the EPA's action level mean?
The EPA's action level is 4 pCi/L: at or above it, the EPA recommends fixing the home, and between 2 and 4 it recommends considering a fix, because there is no known safe level of exposure. Below 2, no action is needed beyond retesting if you start living on a lower level. The number is measured in picocuries per liter of air, and the test kit's lab reports it directly.
The EPA's page on its radon action level recommends homes be fixed at 4 pCi/L or more and that Americans consider fixing their home for levels between 2 and 4 pCi/L. The CDC's testing guidance says testing is the only way to know, that a tester or a hardware-store kit both work, that short-term kits run 2 to 90 days and long-term kits over 90, that the device goes in the lowest lived-in level three feet off the floor in the middle of the room, that a high short-term result should be followed by a second test with action on the average, and that the home should be retested a few months after a fix and before and after converting a basement to living space.
What do you need?
A radon test kit from a hardware store, online, or your state radon office (some states offer them free or discounted), or a certified radon tester if you are buying or selling the home. For a short-term test you also need a stretch of days when the house can stay closed up, with windows shut and exterior doors used only for coming and going, which the kit instructions will describe.
- A short-term or long-term radon test kit with a prepaid lab return
- A spot in the lowest lived-in level: a basement family room, a first-floor bedroom, not a crawlspace or a closet
- Closed-house conditions for the test period, per the kit
- Your state radon office's contact, for kits and a list of certified testers and mitigators
What are the steps?
Choose the level and room, close up the house for the period the kit requires, place the device three feet off the floor in the middle of the room away from drafts and moisture, note the start time, leave it for the test period, seal and mail it the same day the test ends, and read the result against the EPA's 2 and 4 pCi/L thresholds. A high short-term result gets a second test before any decision.
- Pick the lowest level of the house that people use regularly. If the basement is finished or a bedroom is on the lowest floor, that is the level. Done when: you have chosen a room where the device will not be disturbed.
- Read the kit's closed-house instructions. Most short-term kits require windows closed and normal door use for a period before and during the test; heating and cooling can run.
- Place the device three feet off the floor in the middle of the room, away from drafts, fans, sunlight, and high humidity, and away from exterior walls. Write the start date and time on the card.
- Leave it for the full test period. Do not move it.
- At the end, seal it as directed, write the end time, and mail it to the lab the same day. Done when: it is in the mail.
- Read the result. Below 2 pCi/L: no action; note the result and the date. Between 2 and 4: consider a fix; a long-term test helps decide. At or above 4: run a second test (short or long) and average, or run a long-term test.
- If the second result confirms 4 or above, contact your state radon office for a list of certified mitigators and have a radon reduction system installed. Retest a few months after the system is running to confirm it works.
When should you stop and call a pro?
Call a certified radon mitigation contractor if the confirmed level is at or above 4 pCi/L; the fix is usually a sealed pipe through the slab with a fan that vents soil gas above the roof, sized and placed for the house, and it is not a homeowner project.
Hire a certified tester rather than using a kit if you are buying or selling (the EPA recommends it), if a test result will be used in a transaction, or if a first result is near the action level and you want a measurement that will stand up. Test again after any major renovation, especially one that adds living space on a lower level.
What should you record?
Record every test's start and end dates, the room and level, the kit type, and the result, plus the mitigation system's install date, contractor, and the post-installation retest. A buyer will ask, and a result with dates is an answer. Set a retest as a task after any renovation or change in how you use the lower level, and consider a long-term retest every few years as the EPA suggests even below the action level.
Common questions
What radon level is safe?
The EPA says there is no known safe level. It recommends fixing a home at 4 pCi/L or more and considering a fix between 2 and 4. The CDC notes the average American home is about 1.3 pCi/L. Below 2, no action is needed beyond testing again if you start using a lower level of the house.
Do new homes need testing?
Yes. Radon comes from the soil under the house, not from the house's age, and a tight new home can hold more of it. Some new homes are built with radon-resistant features and a capped pipe ready for a fan; those still need a test to know whether the fan is needed.
Short-term or long-term test?
A short-term kit (2 to 90 days) gives a quick screen; a long-term kit (over 90 days) gives the year-round average and better reflects how you live. The CDC's guidance is to follow a high short-term result with a second test and to act on the average or on a long-term result.
What should you do next?
Order a kit today; winter, with the house closed up, is a good season to run it. Radon is one of three invisible air problems in a house; the detector guide covers carbon monoxide, and the attic check covers the moisture that grows mold.
