How often should I test my house for radon?
Test every home at least once, ideally with a long-term test, and test again when you start using a lower level, after major renovations, and before buying or selling. If you have a radon reduction system, retest within 30 days of installation and then at least every two years, and check the system's gauge regularly.
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By Kasra Taheri, Founder, LoclisPublished
Researched and drafted with AI, then checked claim by claim against the sources listed below before it was published. Prices and rules change; the dates beside each source say when it was last checked.
Step by step
Read when to stop and call a pro, further down this page, before you start.
Step 1: Get a baseline result
Run a first test on the lowest lived-in level, then a long-term test if the result is near or above 4 pCi/L.[4]
Step 2: Test after a system goes in
Test within 30 days of installation, but no sooner than 24 hours after the fan starts, using a two- to seven-day measurement.[2]
Step 3: Check the gauge regularly
Look at the system's warning device, usually a manometer, on a regular schedule to confirm the fan is still working.[2]
Step 5: Retest after changes
Test again after major renovations, a new foundation, or when you start using a lower level such as the basement.[1]
Step 6: Test before a sale
Test before listing a home, and save the results and any records of work done to lower radon.[3]
Step 7: Keep your records
File each result with the date, the room, the kit type and the lab report so you can compare tests over the years.
The short answer
There is no fixed calendar for a house that has never been tested: test it now. EPA and the Surgeon General recommend radon testing for every home below the third floor.[3] After that, how often you test depends on what changes in the house and whether you have a radon reduction system.
- No system, low result: test again from time to time, after renovations, and when you start using a lower level.
- A system installed: test within 30 days of installation, then at least every two years, and check the gauge regularly.
- Buying, selling or building: test as part of the deal or soon after you move in.
Why one test is not always enough
Because radon levels vary from day to day and season to season,[1] a single short reading is a snapshot. Virginia recommends long-term testing whenever possible, and a year-long test is the most accurate way to learn a home's year-round average.[4] Even if your result is below 4 pCi/L, EPA suggests you may want to test again sometime in the future.[1]
When to test again
When you start living lower. EPA's advice is that if your living patterns change and you begin occupying a lower level of the home, such as a basement, retest on that level.[1] A teenager's new basement bedroom is a reason to test.
Around renovations. Because major renovations can change the radon level in any home, EPA says to always test again after the work is done.[1] Better still, test the area for radon before converting an unfinished basement into living space,[1] when radon-resistant features are cheapest to add. After remodeling a house that already has a radon system, retest in the lowest lived-in area to make sure the construction did not reduce the system's effectiveness.[2]
In winter. Indoor radon usually reaches its highest levels in the coldest winter months,[5] and most homes test lowest in summer.[4] A winter retest is the one least likely to miss a problem.
If you have a radon reduction system
The first test after installation matters most. Do it within 30 days of installation, but no sooner than 24 hours after the system is running with the fan on.[2] For that check, EPA recommends a two- to seven-day measurement, with windows and doors closed for 12 hours before and during the test.[2] The contractor may test too, but an independent tester, or a test you run yourself, removes any potential conflict of interest.[2]
After that, the routine is short:
- Watch the gauge. If you have a fan-powered system, look at your warning device, usually a manometer, on a regular basis.[2] Make a habit of glancing at it when you change the furnace filter, and note where the liquid sits when the system is new. If the monitor shows the system is not working properly, call a contractor to have it checked.[2]
- Expect fan replacements. Fans may last for five years or more, and manufacturer warranties tend not to exceed five years.[2]
- Leave it on. The fan must run continuously for the system to work correctly.[2]
- Retest on schedule. EPA's advice is to retest at least every two years to make sure radon stays low.[2][1]
New homes
Radon-resistant new construction lowers radon but does not replace a test. Soon after construction is finished and the owner moves in, the home should be tested to see how well the radon-resistant system is working.[6] If the result is 4.0 pCi/L or higher, a certified radon mitigator should be hired to add a fan and make the system active.[6]
Before you sell
EPA recommends testing before you put a home on the market and, if necessary, lowering the radon level.[3] Save the test results and all information about steps taken to fix any problems,[3] because buyers ask. If the house has a system, inform potential buyers and give them information about the system's operation and maintenance.[2]
Stop and call a pro if
- A retest comes back at 4 pCi/L or higher, or higher than your last result by a wide margin.
- The gauge reads level, the fan is silent, or the fan is noisy or vibrating.
- You are finishing a basement or adding a foundation and want radon-resistant features.
- You are buying or selling and need a test from someone outside the deal.
For a full walk-through, see how to test your home for radon, and for prices, what radon mitigation costs in Virginia. Browse more inspection answers or radon testing and mitigation businesses.
Due for a retest or a fan check? Describe the job once and licensed businesses near you can quote.
Common questions
- My house tested low years ago. Should I test again?
- Probably. EPA says that even after a result below 4 pCi/L you may want to test again in the future, and you should retest after major renovations or when you start using a lower level of the house.
- How do I read the gauge on my radon system?
- Many systems use a U-shaped liquid gauge, a manometer, on the pipe. While the fan runs, the liquid usually sits higher on one side than the other. If the two sides are level, or the reading has moved a lot since installation, the fan may have stopped, so call a mitigator to check it.
- Can I turn the radon fan off in summer?
- No. EPA says the fan must run continuously for the system to work correctly. Turning it off lets radon build back up.
- Do I need to retest if I get a new radon fan?
- It is a sensible check. A different fan can change how the system performs, so a short-term test once the new fan has run for at least a day confirms the level is still low.
- What season is best for a retest?
- Winter, if you can. Indoor radon usually peaks in the coldest months and is lowest in summer, so a winter retest is less likely to miss a problem.
Sources
- [1] A Citizen's Guide to Radon (EPA 402/K-12/002), U.S. Environmental Protection Agency. Checked October 27, 2026.
- [2] Consumer's Guide to Radon Reduction (EPA 402/K-10/005), U.S. Environmental Protection Agency. Checked October 27, 2026.
- [3] Home Buyer's and Seller's Guide to Radon (EPA 402/K-24/001), U.S. Environmental Protection Agency. Checked October 27, 2026.
- [4] Radon Frequently Asked Questions, Virginia Department of Health. Checked October 27, 2026.
- [5] Radon Testing and Mitigation, Virginia Department of Health. Checked October 27, 2026.
- [6] Radon Resistant New Construction (RRNC), Virginia Department of Health. Checked October 27, 2026.
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