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When should you test for radon?

By Radon411 Editorial TeamUpdated How we research

Short answer

Test now if your home has never been tested, since EPA recommends testing all homes below the third floor. Then test again after moving into a new home, before and after major renovations, within 30 days of installing a radon system and every two years after, and when you buy or sell.

Next step: pick the right test for your home. Which test to use

The first time is now, if the home has never been tested. Testing is recommended for all homes below the third floor, and every new home should be tested after occupancy, even if it was built radon-resistant.

Renovations call for a test on both sides. If you plan a major structural renovation, test the area before you begin, and because major renovations can change the level of radon in any home, test again after the work is done.

A radon system brings its own schedule: a test within 30 days of installation, then a retest at least every two years to be sure levels remain low. If you start living on a lower floor, such as a basement, retest on that level.

In a sale, test before putting the home on the market, which leaves more time to fix a problem. As a buyer, know the indoor radon level of any home you consider buying, and if it has not been tested, have it tested.

What to do next: if your home has no recent result, start a of at least 48 contiguous hours in the lowest lived-in level, and read the result with the interpreter.

The moments to test, in order

The first time to test is now, if the home has never been tested. After that, testing follows events: anything that changes the house, its radon system or who will live in it.

When to test for radon
WhenWhy
Now, if never testedEPA and the Surgeon General recommend testing all homes below the third floor.
After moving into a new homeEvery new home should be tested after occupancy, even one built radon-resistant.
Before sellingTesting before the home goes on the market leaves time to fix a problem.
When buyingKnow the indoor radon level of any home you consider buying.
Before and after a renovationMajor renovations can change the radon level in any home.
When you start using a lower floorRetest on that level.
After a radon system is installedWithin 30 days, to confirm it worked.
Every two years with a systemTo be sure radon levels remain low.
Some time after a low resultEven a result below 4 pCi/L is worth checking again in the future.

Does the season matter?

Radon levels tend to vary from day to day and season to season, so a is less likely than a to show your year-round average. That cuts both ways: a short test in one season is a snapshot, which is why a high first result is followed up, and why a long-term test of more than 90 days, spanning seasons, gives a better picture of the annual average.

Choosing a test by your timeline
If you needUseHow long
A quick first answerA short-term testTwo days to 90 days, depending on the device; a minimum of 48 hours
The year-round averageA long-term testMore than 90 days
A decision during a home saleTwo short-term tests or a continuous monitorAt least 48 hours

For when radon itself tends to be highest, see when are radon levels highest.

Conditions that make a short test unreliable

Timing also means avoiding the wrong days. Don't run a short-term test of just 2 or 3 days during unusually severe storms or periods of unusually high winds. For any short-term test, keep windows and outside doors closed as much as possible, and for a test of 2 to 4 days, close up at least 12 hours before it starts.

Testing around a home sale

A sale compresses the timeline. If you are selling, test before putting the home on the market; if the home already has a result, a buyer may still ask for a new test, especially if the last test is not recent, for example not within two years, or if the home has been renovated since.

EPA's three short-term radon testing options for a real estate transaction: two tests at the same time, one test then a second, or a continuous monitor, each for at least 48 hours, with what to do after each.
Read this figure as text

If you are testing in a real estate transaction and you need results quickly, any of the following three options for short-term tests are acceptable in determining whether the home should be fixed.

  1. Option 1. Two tests at the same time

    Passive

    Take two short-term tests at the same time in the same location for at least 48 hours.

    What to do nextFix the home if the average of the two tests is 4 pCi/L or more.

    Two tests taken at the same time (simultaneous) would improve the precision of this radon test.

  2. Option 2. One test, then a second

    Passive

    Take an initial short-term test for at least 48 hours. Immediately upon completing the first test, do a second test using an identical device in the same location as the first test.

    What to do nextFix the home if the average of the two tests is 4 pCi/L or more.

    One test followed by another test (sequential) would most likely give a better representation of the seasonal average.

  3. Option 3. A continuous monitor

    Active

    Test the home with a continuous monitor for at least 48 hours.

    What to do nextFix the home if the average radon level is 4 pCi/L or more.

    Both active and passive devices may have features which help to prevent test interference.

Any real estate test for radon should include steps to prevent or detect interference with the test device. Your state radon office can help you decide which option is best.

The three short-term options for testing during a home sale.

Buyers can write the test into the contract: where it goes, who conducts it, what type, when, how results and costs are shared, and when any will be done and who pays. See should I get a radon test with my home inspection.

How long a result stays useful

A radon result has no printed expiry date. What ages it is change: a renovation, a new heating or ventilation system, a change in which floor you live on, or simply time.

Signs a past result needs a new test
Change since the testWhat to do
Structural changes or alterationsRetest
Changes to heating, ventilation or air conditioningRetest
You now use a lower floor than was testedRetest on that floor
A radon system was installed or repairedRetest to confirm it works
The test is more than about two years old, in a saleExpect a buyer to ask for a new one

For the intervals, see how often you should test.

Questions about when to test

When do you need a radon test?

Any time a home below the third floor has never been tested, and then after events that can change the level: moving in, renovating, buying or selling, installing a system, or starting to use a lower floor.

Is winter the best time to test for radon?

Radon varies from season to season, so any single short test is a snapshot. Test whenever you can keep the house closed up, follow up a high result, and use a long-term test for the year-round average.

Should I test for radon before buying a house?

Yes. Know the indoor radon level of any home you consider buying, and if it has not been tested, have it tested.

Should I test after installing a radon system?

Yes, within 30 days of installation, and then at least every two years to be sure levels remain low.

When is radon testing required?

Testing is recommended for every home below the third floor. Some states require testers to follow a specific protocol, and some require radon information to be disclosed to buyers. See is a radon test required.

Can I test during a storm?

Not with a short-term test of 2 or 3 days: avoid unusually severe storms and periods of unusually high winds.

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