How to test for radon
Run a radon test before closing, during your inspection period, in the lowest level anyone could regularly use, for at least 48 hours with windows and outside doors closed. EPA says to fix the home at 4 pCi/L or higher and to consider fixing it between 2 and 4. If the result is high, negotiate the fix before closing.
Where to run a radon test before closing
You're measuring the air where a person could end up spending time, which may not be where the seller lives now. EPA's home buyer guide says to test the lowest level that could be used regularly, finished or not, because you might turn that basement into a playroom. EPA recommends testing all homes below the third floor.
Placement can ruin a result. Avoid closets, stairways, hallways, crawl spaces, kitchens, bathrooms, laundry rooms and furnace rooms. Put the device at least 20 inches off the floor, away from drafts, high heat, high humidity and exterior walls.
For tests under four days, close windows and outside doors at least 12 hours before starting, and don't test during severe storms or high winds.
Because a seller controls the house during the test, EPA suggests guarding against interference. Options include a continuous monitor that logs swings, tamper seals on windows, motion detectors, and a signed non-interference agreement. If the seller offers an old result, ask who ran it, where, and when. A new test makes sense if the last one is more than about two years old, if the home has been renovated, or if you'll use a lower floor.
How to handle a radon test before closing, step by step
- Ask the seller first
Request any earlier results and details on any mitigation system. Confirm the fan runs and that the gauge on the pipe shows suction.
- Choose a test option
EPA accepts three for real estate: two passive tests side by side, two passive tests back to back, or a continuous monitor. Each runs at least 48 hours.
- Hire a qualified tester
Your state radon office can tell you who's licensed or certified. A DIY kit is possible but offers less protection from tampering.
- Set closed-house conditions
Windows and outside doors stay shut except for normal entry and exit, starting 12 hours before a short test.
- Check the test stayed intact
Ask your tester how interference was prevented, and read any hour-by-hour data for odd swings.
- Act before your deadline
Book the test early in your inspection period. Ask how fast results come back, since mailed kits can take days or weeks.
- Follow up after move-in
A long-term test of more than 90 days gives a better picture of your year-round average.
Radon test results and when to fix the home
| Result | EPA's guidance | What to do |
|---|---|---|
| Below 2 pCi/L | Reducing levels this low is difficult | Keep the report. Retest after major renovations or if you start using a lower floor |
| 2 to 3.9 pCi/L | Consider fixing | No level is risk-free. Discuss options and plan a long-term test |
| 4 pCi/L or higher | Fix the home | Negotiate mitigation before closing |
For context, EPA puts the average indoor level at about 1.3 pCi/L and outdoor air at about 0.4. Over a lifetime at 4 pCi/L, it estimates about 7 lung cancers per 1,000 never-smokers and about 62 per 1,000 smokers. If you ran two passive tests, use their average. With a continuous monitor, use the average it reports.
Radon mitigation before closing: what a fix involves
A high result can be fixed. EPA says even very high levels can be brought down, and most homes can be fixed for about the cost of other common repairs. One cost guide gives about $771 to $1,185 as typical, about $800 to $2,500 for a sub-slab system with a fan, and up to about $3,000 for large or complex homes. Budget for the fan's electricity too. Your agent can help you ask for a repair or a credit.
Most fixes use a vent pipe and fan. EPA doesn't recommend sealing cracks alone, because that hasn't been shown to lower radon reliably. Ask for a detailed written proposal, and check your state radon office for licensing rules, since they vary.
EPA recommends a retest by an independent tester after the work, and warns of a conflict of interest when one firm both tests and mitigates. On a private well with high air results, test the water too.
How long does a radon test take, and other questions
Do new homes need a radon test?
Yes. EPA says any home can have a radon problem, including new, well-sealed homes and homes without basements. For a new build, ask if radon-resistant features were used and if the home has been tested.
Can I rely on my neighbor's radon result?
No. EPA warns that homes next to each other can have different levels. Testing your own house is the only way to know.
How long does a radon test take?
All tests should run at least 48 hours, and some devices need longer, such as a 7-day charcoal canister. Short-term tests last from two to 90 days, and long-term tests run more than 90 days.
What you’ll need
General guidance for U.S. homes, not professional advice. For gas, electrical and structural work, call a licensed pro.