The essentials in 30 seconds
EPA and the Surgeon General recommend testing every home below the third floor. A short-term test stays in place for 2 to 90 days and gives a quick answer; a long-term test stays more than 90 days and better reflects your year-round average. Every test should run for at least 48 hours. Put the kit in the lowest lived-in level, in a room you use regularly (not the kitchen or bathroom), at least 20 inches above the floor, away from drafts, heat, humidity and outside walls. If a short-term result is 4 pCi/L or higher, confirm it with a second test; EPA recommends fixing the home at 4 pCi/L or more.
- For 2- to 3-day tests, close windows and outside doors at least 12 hours before you start and keep them closed.
- The average US home has about 1.3 pCi/L; outdoor air has about 0.4 pCi/L.
- In the UK, UKHSA tests over three months with two detectors; the Action Level is 200 Bq/m³.
Why every home should be tested
Radon comes from the natural breakdown of uranium in soil and rock and enters through cracks in floors, construction joints, gaps around pipes and cavities in walls. Any home can have a problem: new or old, drafty or well sealed, with or without a basement. EPA estimates that nearly 1 in 15 US homes has an elevated level.
Two homes side by side can give very different results, so a neighbor's test tells you little about yours. Radon maps show where high levels are more likely, but only a test in your own home gives you your number.
Short-term vs long-term radon tests
| Short-term test | Long-term test | |
|---|---|---|
| Time in place | 2 to 90 days, depending on the device | More than 90 days |
| Common devices | Charcoal canisters, alpha track, electret ion chamber, charcoal liquid scintillation, continuous monitors | Alpha track and electret detectors |
| Best for | A quick first answer, a confirmation when a result is high, home sales | Your year-round average, for a final decision |
| Limit | Radon varies day to day and season to season, so it is less representative | You wait months for the answer |
Devices are also passive or active. Passive kits need no power: you expose them, seal them and post them to a laboratory. Active devices, such as continuous radon monitors, plug in, record hourly readings and can reveal unusual swings during the test. Whichever you choose, use a device from a qualified laboratory; your state radon office can point you to one.
How to test for radon step by step
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01
Pick the test level
Use the lowest level of the home you live in regularly: the basement if you use it often, otherwise the ground floor.
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02
Pick the room
Choose a room you spend time in, such as a living room, den, playroom or bedroom. Skip kitchens and bathrooms.
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03
Close the house
For a 2- to 3-day test, close windows and outside doors at least 12 hours before you start, and keep them closed apart from normal coming and going.
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04
Place the kit
At least 20 inches above the floor, where nobody will move it, away from drafts, high heat, high humidity and exterior walls.
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05
Record the start
Write down the start date and time as the instructions ask.
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06
Leave it alone
Keep it in place for the full time on the package.
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07
Seal and send it
Record the end date and time, reseal the package and post it to the lab straight away. Results usually arrive within a few weeks.
What closed-house conditions mean during a radon test
Closed-house conditions keep the result from being diluted by outdoor air. During short-term tests:
- Keep windows closed and outside doors closed except for normal entry and exit.
- Run heating and air conditioning normally if they recirculate indoor air.
- Switch off fans and machines that bring in outdoor air, such as a whole-house fan.
- Short bursts of exhaust fans (a bathroom or kitchen fan) are fine, and so is the fan of a radon reduction system, which must stay on.
- Reschedule 2- to 3-day tests if severe storms or very high winds are forecast.
How to read your radon test results
EPA's sequence is simple: a first short-term test, then a follow-up if the result is 4 pCi/L or higher.
| Your result | What it means | What to do next |
|---|---|---|
| Below 2 pCi/L | Low, close to typical indoor levels | Test again sometime in the future, and after major changes to the home |
| 2 to 4 pCi/L | Below the action level but still some risk | Consider fixing the home; a long-term test gives a firmer figure |
| 4 pCi/L or more on a first short-term test | Possibly high | Take a follow-up test: long-term for the best picture, or a second short-term test if you need results quickly |
| More than 8 pCi/L on a first short-term test | Twice the action level | Take a second short-term test right away |
| 4 pCi/L or more on a long-term test, or as the average of two short-term tests | Confirmed high | Fix the home with a radon reduction system |
Results close to 4 are the hardest to call. EPA notes that when two short-term tests average 4.1 pCi/L, there is about a 50 % chance that the year-round average is slightly below 4. The closer you are to the line, the more a long-term test helps.
When to test for radon again
- After a radon system is installed: within 30 days, but at least 24 hours after the fan starts, with a two- to seven-day test.
- Every two years with a mitigation system in place, to check levels stay low.
- After major renovations, such as finishing a basement, and ideally before starting them too.
- When you start living on a lower level, for example turning the basement into a bedroom.
- In new homes, even those built with radon-resistant features, once you move in.
- If your first result was low, it is still worth testing again at some point.
Radon testing when you buy or sell a home
Home sales move fast, so EPA's home buyer's guide adapts the steps:
- Test the lowest level that could be used regularly, finished or not, since a buyer may turn the basement into a family room.
- Avoid closets, stairways, hallways, crawl spaces and enclosed rooms with high humidity or fast-moving air, such as kitchens, bathrooms, laundries and furnace rooms.
- Choose one of three short-term options: two passive tests at the same time in the same place (EPA's citizen's guide suggests about four inches apart), two passive tests one after the other, or a continuous monitor, each for at least 48 hours. Fix the home if the average is 4 pCi/L or more.
- Guard against interference: testers can use continuous monitors that flag unusual swings, motion detectors, tamper-proof seals on windows and a signed non-interference agreement from the occupants.
- Prefer an independent tester: buyers often want a test from someone with no stake in the sale; your state radon office can help you find one.
- If the house has a radon system, check the fan is running properly before and during the test.
Sellers who test early and fix any problem avoid delays: EPA notes that homes where radon was fixed sell without trouble, and the system can even be a selling point.
Radon testing in the UK
UKHSA's UKradon service sends two detectors: one for the living area and one for an occupied bedroom, where you spend most time. They stay in place for three months to average out short-term swings, then go back by post; results usually arrive within four weeks and give your yearly average compared with the Action Level of 200 Bq/m³. Shorter tests carry more uncertainty, and results are less reliable if the home stands empty for more than a few weeks or building work is going on. UKradon also publishes maps showing the chance of a high level in each area. As a guide, 1 pCi/L equals 37 Bq/m³.
Do you need to test your water for radon
Test the air first. Radon from the soil is usually a much larger risk than radon from water, which mainly matters when it escapes into the air during showers and laundry. If your air level is high and you have a private well, test the water as well; if you use a public supply drawn from groundwater, ask your water supplier.
Radon testing: frequently asked questions
How long does a radon test take?
Short-term tests take 2 to 90 days, and every test should run at least 48 hours. Long-term tests take more than 90 days; the UK service uses three months.
Where should I place a radon test kit?
In the lowest lived-in level, in a room you use regularly, at least 20 inches above the floor, away from drafts, heat, humidity and outside walls. Skip kitchens and bathrooms.
What is a safe radon level?
No level is completely safe. EPA recommends fixing at 4 pCi/L or more and considering it from 2 pCi/L.
Can I test for radon myself?
Yes. Do-it-yourself kits from a qualified laboratory are widely available. For a home sale, buyers often prefer a qualified independent tester.
Can I open windows during a radon test?
Keep them closed during short-term tests, and for 2- to 3-day tests from 12 hours before you start. Normal use of doors is fine.
What should I do if my radon test is high?
Confirm it with a second short-term or a long-term test. If the result stands at 4 pCi/L or more, contact a certified radon mitigator.
How often should I test for radon?
Retest every two years if you have a mitigation system, after renovations and whenever you start using a lower floor.
Does radon have a smell?
No. You cannot see, smell or taste it, which is why testing is the only way to know.
Sources
Official radon guidance, checked on 27 October 2026.
- US EPA · A citizen's guide to radon ↗Who should test, short- and long-term tests, how to place a kit, closed-house conditions, testing steps, what results mean, retesting and home sales.
- US EPA · Home buyer's and seller's guide to radon ↗Test location in real estate deals, places to avoid, simultaneous and sequential tests, continuous monitors and interference safeguards.
- US EPA · Consumer's guide to radon reduction ↗Minimum 48-hour tests, passive and active devices, post-mitigation test.
- UKHSA · UKradon: measuring radon ↗Two detectors, three-month tests, rooms to test and limits of shorter tests.
- UKHSA · UKradon: Action Level and Target Level ↗200 and 100 Bq/m³.
Ready to test?
Choose the lowest room you use every day, close the house for 12 hours and set the kit at least 20 inches above the floor.