What radon is
Radon is a radioactive gas from the natural breakdown of uranium in soil and rock. It has no color or smell. It moves up through the ground and into homes through cracks in foundations, sump pits, crawlspaces, and gaps around pipes.
The EPA and the Surgeon General identify radon as the second leading cause of lung cancer in the United States after smoking. Any home can have elevated radon: new or old, with or without a basement, in any state. The only way to know your level is to test.
Short-term or long-term
Radon changes from day to day and season to season, usually highest in winter when the house is closed and the furnace pulls air up from below.
| Use | Kit | Why |
|---|---|---|
| First test of a home | Short-Term | A result in about a week. Tells you whether to look further. |
| Buying or selling | Real Estate Pair | Two short-term kits side by side, one of the EPA’s transaction options. Check your state first. |
| Confirming a high result | Short-Term, then Long-Term | The EPA asks for a follow-up before you fix anything. |
| Your yearly average | Long-Term | 91 days to a year. Covers the seasons. The right basis for a mitigation decision. |
Placement and conditions
Where to put the device
The lowest level of the home you live in or could live in: the basement if it is finished or used, otherwise the first floor. A room you use, on a shelf or table at least 20 inches above the floor, at least 3 feet from windows and outside doors, away from kitchens, bathrooms, closets, crawlspaces, drafts, direct sun, and high humidity.
Closed-house conditions
For a short-term test, keep windows and outside doors closed from 12 hours before the test until it ends. Normal entry and exit is fine. Run heating and cooling as usual. Do not run whole-house fans or open windows for ventilation. Long-term tests need no closed-house conditions; live normally.
Timing
Write the start and stop times on the device tag and log them in My Tests. Short-Term: 48 to 96 hours. Long-Term: 91 days minimum, up to a year. Mail the device the day you stop; the laboratory accepts a short-term device up to 10 days after the stop time.
Reading your result
Your report gives the average radon concentration during the test window in picocuries per liter of air (pCi/L), with the laboratory’s uncertainty and detection limit. The EPA action level is 4 pCi/L. The EPA suggests considering mitigation between 2 and 4 pCi/L. Outdoor air averages about 0.4 pCi/L.
A single short-term result at or above 4 pCi/L calls for a second test before you mitigate. If the average of the two is 4 or higher, fix the home. A long-term result is more reliable than a short-term one and can stand on its own.
If you need to fix it
Mitigation is routine. The most common system, sub-slab depressurization, uses a pipe and a small fan to draw gas from under the foundation and vent it above the roof. Most systems bring a home under 2 pCi/L. Use a contractor listed by NRPP or NRSB or licensed by your state (see local resources), and test again after installation and every two years after that.
Questions
Does a new house need a test?
Yes. Radon depends on the soil and the house’s pressure, not its age. Radon-resistant construction lowers risk but does not replace a test.
My neighbor tested low. Do I still need to?
Yes. Levels differ house to house on the same street.
How often should I retest?
Every two years, after any major renovation, after adding a mitigation system, and before you sell.
Can I test an apartment or a slab home?
Yes. Test the lowest level you live on, following the same placement rules.
How accurate is a short-term test?
The laboratory reports every result with its measurement uncertainty. Short-term tests are reliable for the window they cover; the EPA’s follow-up rules exist because radon changes over time, not because the measurement is doubtful.
Sources: U.S. EPA, A Citizen’s Guide to Radon; U.S. EPA, Home Buyer’s and Seller’s Guide to Radon. Laboratory procedures: our laboratory.