Test your home for radon this winter: a step-by-step guide
Published October 30, 2026
Why the heating season is a practical time to test for radon, how to place a test kit so the result means something, what the numbers mean, and how a mitigation system fixes a high reading.
Radon is a radioactive gas that seeps out of soil and rock and into houses through the foundation. You can’t see, smell or taste it. The U.S. Environmental Protection Agency (EPA) estimates radon causes about 21,000 lung cancer deaths a year, making it the leading cause of lung cancer among people who have never smoked. It turns up in every state and in every kind of house, new or old, with or without a basement. The only way to know your level is to test, and a do-it-yourself test kit costs less than a tank of gas.
Why the heating season is a practical time to test
A short-term radon test needs “closed-house conditions”: windows and outside doors kept shut as much as possible during the test, and for tests that last only 2 or 3 days, starting at least 12 hours before. In summer that is hard to do; in December it is how most houses already run. Several state radon programs, including Pennsylvania’s, point to the colder months as a good time to test for that reason. January is also National Radon Action Month, when many states and health departments promote testing.
Radon levels change from day to day and season to season, so a single short test is a snapshot, not your year-round average. That is why EPA’s process uses a follow-up test before you decide to fix anything.
How to test, step by step
- Buy a short-term test kit (2 to 90 days, depending on the device) from a hardware store, online, or your state radon program, which sometimes offers them free or discounted. If you are buying or selling a home, consider hiring a certified radon measurement professional instead.
- Close windows and outside doors at least 12 hours before a 2–3 day test and keep them closed during it. Your furnace or AC fan can run normally, but don’t run fans that pull in outside air. Skip 2–3 day tests during unusually severe storms or high winds.
- Put the kit on the lowest lived-in level of the home: the basement if you use it regularly, otherwise the first floor. Choose a room you use, like a living room, den or bedroom, not a kitchen or bathroom.
- Place it at least 20 inches above the floor, away from drafts, high heat, high humidity and exterior walls, where nobody will move it.
- Leave it for exactly the time on the package, then seal it and mail it to the lab right away. Write down the start and end dates and times; most labs ask for them.
What your result means
Radon is measured in picocuries per liter of air (pCi/L). EPA’s action level is 4 pCi/L. The average indoor level is about 1.3 pCi/L, and EPA suggests considering a fix between 2 and 4 pCi/L, since there is no known safe level.
- Below 4 pCi/L on a short-term test: no follow-up needed now. Retest in a couple of years (Ohio’s health department suggests every two years), and after big renovations.
- 4 pCi/L or higher: test again in the same spot. For a better picture of your year-round level, use a long-term test (more than 90 days). If you need an answer sooner, run a second short-term test.
- More than about 8 pCi/L (twice the action level) on the first test: EPA says do the second short-term test right away rather than waiting months for a long-term one.
- Fix the home if the long-term result is 4 pCi/L or more, or consider fixing it if the average of two short-term tests is 4 pCi/L or more.
How a high reading gets fixed
The usual fix is a soil suction system: a pipe runs from under the basement slab or crawl space to a fan that vents radon above the roof. EPA says some systems cut radon levels by up to 99 percent and that most homes can be fixed for about the same cost as other common home repairs. Sealing foundation cracks helps the system work, but sealing alone isn’t a reliable fix.
Use a contractor trained and certified in radon mitigation (your state radon office or a national certification program can tell you who qualifies), and get more than one written estimate, since price depends on how the house was built. After installation, retest to confirm the level dropped, and check the system’s pressure gauge or alarm now and then. Air duct cleaning, air purifiers and dehumidifiers do not reduce radon.
Special cases
- Finishing a basement? Test before you start. If the level is high, radon-resistant steps are cheap to add during the renovation. Test again when the work is done.
- Private well? Radon can also come from well water. Ask your state radon office about testing the water.
- Buying or selling? EPA’s home buyer’s and seller’s guide covers testing during a sale; buyers often prefer a tester who has no stake in the deal.
- Rental property? A test is cheap and gives you and your tenants a clear answer.
Put it on the calendar
Set a reminder to test this winter and retest every two years. A free Estodia account keeps radon testing on each home’s maintenance plan alongside the furnace tune-up and gutter cleaning, and when a home needs a mitigation system, you can request quotes from pros without sharing your phone number or email with them.
Sources: EPA: A Citizen’s Guide to Radon (PDF); EPA: Health risk of radon; EPA: National Radon Action Month; EPA: Find a radon test kit or measurement and mitigation professional; PA DEP: Radon in the home; Ohio Department of Health: Radon data.
Quick answers
What is a safe radon level?
There is no known safe level, but EPA’s action level is 4 pCi/L: fix the home at or above that (confirmed by a follow-up test), and consider fixing it between 2 and 4 pCi/L. The average indoor level in the U.S. is about 1.3 pCi/L.
Is winter a good time to test for radon?
Yes, it is practical. Short-term tests need windows and outside doors kept closed, which is easy in cold weather. Levels vary by season, so if a winter test shows 4 pCi/L or more, follow EPA’s steps and confirm with a second test before deciding on a fix.
Can I test for radon myself?
Yes. Low-cost do-it-yourself kits are sold online and in hardware stores, and some state radon programs offer them. Follow the instructions, place the kit on the lowest lived-in level and mail it to the lab promptly. For a home sale, many buyers and sellers use a certified tester.
How much does radon mitigation cost?
EPA says most homes can be fixed for about the same cost as other common home repairs, but the price depends on the foundation, the soil and how high the level is. Get written estimates from more than one certified mitigation contractor and ask each to include a post-installation test.