Testing is the only way to know how much radon is in your home. You can’t see, smell or taste it, and two houses on the same street can have very different levels. A do-it-yourself test kit takes a few minutes to set up. EPA and the Surgeon General recommend testing every home below the third floor (EPA, A Citizen’s Guide to Radon).
The short answer
- Put a short-term test kit in the lowest level of your home that you use regularly.
- Keep windows and outside doors closed for 12 hours before the test and during it.
- Leave it for as long as the package says (at least 48 hours), then mail it to the lab straight away.
- If the result is 4 pCi/L or higher, do a second test to confirm it. If the confirmed level is 4 pCi/L or more, EPA recommends fixing your home.
The rest of this guide explains each step and the choices along the way.
Short-term or long-term test?
Radon levels change from day to day and from season to season, so the length of the test matters (EPA, Citizen’s Guide).
| Short-term test | Long-term test | |
|---|---|---|
| How long it stays in your home | 2 to 90 days, depending on the device | More than 90 days |
| Common devices | Charcoal canisters, charcoal liquid scintillation, electret ion chambers, alpha track detectors, continuous monitors | Alpha track and electret detectors |
| What it tells you | A snapshot. Quick, but less likely to match your year-round average | A result closer to your home’s year-round average |
| Best for | A first test, or when you need an answer fast (a home sale) | Confirming a result when you have time |
All radon tests should run for at least 48 hours, and some devices need longer, such as a 7-day charcoal canister (EPA, Home Buyer’s and Seller’s Guide to Radon).
Passive kits and electronic monitors
Most store-bought kits are passive: they need no power, you leave them in place, then send them to a lab. They are generally inexpensive. Active devices, such as continuous radon monitors, need power, record readings every hour and give an average for the test period. They usually cost more (EPA, Consumer’s Guide to Radon Reduction). Whatever you choose, use a device from a qualified laboratory.
Where to get a test kit
- Stores and online. Many radon test kits are sold online and in home improvement stores (EPA).
- Discounted kits. The National Radon Program Services at Kansas State University sells discounted kits online (sosradon.org).
- Your state. Some states offer free or discounted kits. Your state radon program can tell you what is available.
- A professional. You can hire a qualified radon tester instead. EPA suggests this if you prefer it, and it is common when a home is being bought or sold.
How to set up the test
These steps come from EPA’s guidance for do-it-yourself tests (Citizen’s Guide; Home Buyer’s and Seller’s Guide).
Pick the room. Test in the lowest lived-in level of the home: the basement if you use it often, otherwise the first floor. Choose a room you use regularly, such as a living room, playroom, den or bedroom. Don’t test in the kitchen or bathroom.
Pick the spot. Place the kit at least 20 inches above the floor where it won’t be disturbed, away from drafts, high heat, high humidity and exterior walls.
Close up the house. For a short-term test, keep windows and outside doors closed as much as possible, apart from normal coming and going. For a test shorter than four days, close them at least 12 hours before you start. Heating and air conditioning fans that recirculate air can run; fans that bring in outside air should not. A radon system fan, or a small exhaust fan used briefly, is fine.
Watch the weather. Don’t run a short test (under four days) during severe storms or very high winds.
Record the times. Write down the start date and time, and the stop date and time when the test ends.
Mail it promptly. Reseal the kit and send it to the lab on the package right away. Results usually arrive within a few days or weeks.
What to do with the result
Radon is measured in picocuries per liter of air (pCi/L). EPA’s testing steps are (Citizen’s Guide):
- Take a short-term test. If the result is 4 pCi/L or higher, do a follow-up test to be sure.
- Follow up with either a long-term test, for a better picture of your year-round level, or a second short-term test, if you need an answer quickly. If the first result is more than twice the action level (above 8 pCi/L), take the second short-term test straight away.
- Decide. If your long-term result is 4 pCi/L or more, fix your home. If you used two short-term tests, consider fixing your home if their average is 4 pCi/L or more.
How to read the number
| Result | What EPA says |
|---|---|
| 4 pCi/L or more | Fix your home (after a confirming test) |
| 2 to 4 pCi/L | Consider fixing. Levels below 4 still carry some risk |
| Below 2 pCi/L | Below EPA’s levels for action. Most homes that are fixed can be brought to 2 pCi/L or below |
For context, the average indoor level in the US is about 1.3 pCi/L and outdoor air is about 0.4 pCi/L. EPA says no level of radon is completely safe (Citizen’s Guide). The World Health Organization recommends a national reference level of 100 Bq/m³ (WHO), which is about 2.7 pCi/L.
Results close to 4 are less certain. If two short-term tests average 4.1 pCi/L, there is about a 50% chance that your year-round average is somewhat below 4 (Citizen’s Guide). A long-term test settles it if you have the time.
To see how your result compares with homes near you, look up your county below. If your home needs fixing, read how radon mitigation systems work and what they typically cost.
Testing when you buy or sell a home
Home sales move fast, so EPA’s real estate guidance is a little different (Home Buyer’s and Seller’s Guide):
- Test the lowest level that could be used regularly, finished or not, because a buyer may plan to use a basement the seller doesn’t.
- Any of three short-term options is acceptable: two passive tests side by side for at least 48 hours; two passive tests one after the other in the same spot; or a continuous monitor for at least 48 hours. Fix the home if the average is 4 pCi/L or more.
- Guard against interference. Moving the device or opening windows invalidates the result. Testers can use continuous monitors that log unusual swings, motion detectors, tamper seals on windows, and a signed non-interference agreement with the occupants.
Buyers often want the test done by someone who is not involved in the sale. A qualified tester can do that and explain the report.
Hiring a radon tester
Your state radon program can point you to qualified testers, and many states license radon professionals. States that receive EPA radon grants list only providers credentialed by the state or by one of the two national programs: the National Radon Proficiency Program (NRPP) and the National Radon Safety Board (NRSB) (EPA).
When to test again
- After any radon fix, to confirm it worked, and then at least every two years (EPA, Consumer’s Guide).
- After major renovations, such as finishing a basement, because they can change radon levels.
- When you start using a lower level of the home, such as a basement, test on that level.
- Even after a low result, EPA suggests you may want to test again at some point in the future (Citizen’s Guide).