How to Test Your Home for Radon: Kits, Monitors and What Results Mean
How to test a home for radon: short- and long-term tests, continuous monitors, where to place them, what 2 and 4 pCi/L mean, and what to do next, from EPA guidance.
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To test your home for radon, place a short-term test kit or a continuous radon monitor on the lowest level you regularly use, at about table height, away from drafts, windows and exterior walls, with windows and doors kept closed except for normal coming and going. If the result is 4 picocuries per liter (pCi/L) or higher, confirm it with a long-term test or a second short-term test, and if the confirmed level is 4 or more, the EPA recommends fixing the home. The EPA also suggests considering a fix between 2 and 4 pCi/L.
Radon is a colorless, odorless radioactive gas from uranium in soil and rock. It enters through cracks and gaps in foundations and can build up in any home, old or new, with or without a basement. The EPA estimates it causes about 21,000 lung cancer deaths a year in the US and says it is the leading cause among people who have never smoked.
Step 1: Choose a test
| Test | What it tells you | Cost and effort |
|---|---|---|
| Short-term kit (a few days) | A snapshot; good as a first test | Low cost; mail to a lab |
| Long-term kit (more than 90 days) | Closer to your year-round average | Low cost; one result after months |
| Continuous digital monitor | Ongoing short- and long-term averages | Higher upfront cost; no lab fees |
| Certified professional test | A documented result for a home sale or mitigation | Professional fee |
The EPA's advice is to start with a short-term test, then follow up if it shows 4 pCi/L or more. A continuous monitor does both jobs at once and keeps watching afterward. Our best radon detectors guide compares monitors.
Step 2: Place it correctly
- Lowest lived-in level. A finished basement you use, otherwise the ground floor. The EPA says to retest on a lower level if you start using it.
- About table height, not on the floor.
- Away from drafts, windows, exterior walls, vents and sump pits.
- Not in kitchens, bathrooms or laundry rooms, where humidity and fans affect the result.
- Closed-house conditions for short-term tests: keep windows and outside doors closed, apart from normal use, during the test and for 12 hours before.
Step 3: Read the result
| Result | Bq/m3 | EPA guidance |
|---|---|---|
| Below 2 pCi/L | Below 74 | Lower risk; there is no known safe level, and the US average indoor level is about 1.3 pCi/L |
| 2 to 4 pCi/L | 74 to 148 | Consider fixing |
| 4 pCi/L or more | 148 or more | Confirm with a follow-up test, then fix |
| More than 8 pCi/L on a first short-term test | More than 296 | Take a second short-term test immediately |
Radon rises and falls with weather and season, often higher in winter when houses are closed up. That is why a single short test is a starting point and a long-term average is the number to act on.
Step 4: If you need to fix it
The most common fix is a sub-slab depressurization system: a vent pipe and fan that draw radon from beneath the foundation and release it above the roof. The EPA recommends using a qualified radon mitigation contractor; many states certify them. After installation, retest, and if you own a continuous monitor, keep it running to confirm the system keeps levels down.
What does not fix radon: air purifiers, even with carbon filters; opening windows only during a test; sealing cracks alone, which the EPA says is not usually enough on its own. See our note on purifiers and radon in the basement purifier guide.
Common questions about radon testing
Does a new house need testing?
Yes. Radon depends on the soil and how air moves through the house, not the age of the building. The EPA recommends testing all homes, and some newer homes are built with radon-resistant features that still need testing to confirm.
What about apartments?
The EPA's guidance focuses on the lowest lived-in levels; ground-floor and basement apartments are the most likely to have elevated radon. Ask your landlord whether the building has been tested, or test yourself.
How often should I retest?
After any renovation that changes the lowest level, after mitigation, and every few years otherwise. A continuous monitor makes this automatic.
For a wider view of your home's air, see our guide to measuring indoor air quality.
Frequently asked questions
How do I test my house for radon?
Place a short-term test kit or a continuous monitor on the lowest lived-in level, at table height, away from drafts and exterior walls, with the house closed up. If the result is 4 pCi/L or more, confirm with a follow-up test.
What is a safe radon level in a home?
The EPA says there is no known safe level. It recommends fixing homes at 4 pCi/L or more and considering a fix between 2 and 4 pCi/L; the US average indoor level is about 1.3 pCi/L.
How long does a radon test take?
Short-term tests run for a few days; long-term tests for more than 90 days. A continuous monitor shows a first reading within hours or minutes and builds a long-term average over months.
Do I need to test for radon if I do not have a basement?
Yes. Radon can enter any home through the foundation; the EPA recommends testing every home on its lowest lived-in level.
How do you get rid of radon?
Usually with a sub-slab depressurization system installed by a qualified radon mitigation contractor, followed by retesting. Air purifiers and sealing cracks alone do not solve it.
Is radon worse in winter?
Levels often rise when houses are closed up in colder months. That is one reason to rely on a long-term average rather than one short test.
Sources
- A Citizen's Guide to Radon, US Environmental Protection Agency
- What is EPA's Action Level for Radon and What Does it Mean?, US Environmental Protection Agency
- A Radon Guide for Tenants, US Environmental Protection Agency
- View Plus product sheet, Airthings
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