What Is Radon Testing?

Learn how and why it's important to test your home for radon

Radon Mitigation System

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Radon testing detects the radioactive gas radon, which naturally occurs in the soil under and around homes. Radon is invisible and odorless, so testing is the only way to know if your home has it. Exposure to high levels of radon poses serious health risks.

Testing for radon indicates if your home's radon levels are within acceptable safety limits. Do-it-yourself tests are inexpensive and easy to deploy. Reducing radon in the home can be as simple as sealing cracks and improving ventilation or might require a vent pipe to be installed in the foundation to vent the radon gas to the outside

What Radon Testing Is

Radon is produced when the radioactive metals uranium, thorium, or radium break down in rocks, soil, and groundwater, producing a gas. Radon is found everywhere, but some places have more of it than others.

Radon testing measures the presence and level of radon in the home either with charcoal canisters or with a special film. The charcoal canister method tests for radon over a short period, usually two to seven days. The film (or alpha track) method runs from three months to a year.

Fun Fact

Large sections of the Northeast and northern Midwest United States consistently test the highest for radon, with levels above 4 pCi/L. Areas of Washington, Oregon, Southern California, South Carolina, Georgia, and Texas test the lowest.

Areas of the Home Likely to Have Radon

Areas in the home that are most likely to have higher levels of radon are those that are at or below ground level or to exposed earth. Even areas that aren't located in lower areas may have elevated radon levels simply because occupants spend more time in them.

  • Basements
  • Crawl spaces
  • Living rooms
  • Bedrooms
  • Any other area of the home that is frequently occupied or occupied for long periods

Radon can come through cracks in floors or walls, suspended floors, construction joints, or spaces around service pipes.


At one time, it was believed that granite countertops contained enough radon to pose a health risk to users. More recent guidance from the EPA indicates that, though granite does contain trace radioactivity, the radon in the stone is not a major contributor to radiation in the home.

How to Test for Radon

The most common method of testing for radon is with short-term tests, such as charcoal canisters, or with longer-term film or alpha track detectors. Both are do-it-yourself tests that are inexpensive and easy to do.

Charcoal Canister Short-Term Radon Testing

Charcoal canisters are placed in the home for a short period of time, typically two to seven days. During this time, the charcoal absorbs radon gas from the air.

The test must follow a strict schedule. Upon completion, the test is mailed to a lab for testing.

Short-term radon tests produce relatively fast results. But the results are less accurate than with other methods because the tests capture only a small window of time.

Charcoal-based radon test kits cost from $18 to $60. Test kits subsidized by National Radon Program Services, a cooperative of the EPA and Kansas State University, cost $17 each, with all shipping and lab costs included.

Alpha Track Long-Term Radon Testing

Alpha track radon detectors use a special film that is exposed to the air in the home for a longer period of time than the charcoal canisters, typically three months to a year. 

After testing, the film is then sent to a laboratory for analysis to determine the radon levels in the home.

Radon levels fluctuate from season to season and even from day to day. So, long-term radon testing produces more accurate radon level results since they are averaged out over a long period of time.

Alpha track radon test kits cost $30 to $40 each. National Radon Program Services offers subsidized alpha track kits for $27 each, all costs included.

Continuous Radon Monitors

Electronic continuous radon monitors, per the name, continuously measure the levels of radon in the air and can provide accurate long-term readings since they are always running. 

Continuous radon monitors have passive diffusion chambers that collect and test the air. Continuous monitors begin at around $1,000 and are most often used commercially for activities such as home inspection.

Lower-cost monitors that connect to a smartphone start at about $200. Using alpha spectrometry to test for radon, these units are most accurate over minimum 30-day test periods that encompass a range of temperature and humidity levels.

When and How Often to Test for Radon

  • When buying or selling a house
  • If a radon mitigation system is in place—every two years
  • After home remodels, particularly projects that open up the basement for living

As a Home Buyer or Seller

Buying or selling a home are events that usually trigger radon testing, especially if your state or local government requires radon disclosures.

As a seller, you'll want to make sure that the last radon test was within the last two years and that it was done correctly. 

As a buyer, you'll want to make sure that the last test was within two years of the intended purchase date. If not, a radon test should be performed and results returned before the closing date.

As an Occupant of the Home

As an ongoing occupant of the home, there is no set schedule or frequency for testing for radon. But you might want to test for radon if:

  • The lowest level of your home will now be occupied, as if with a basement finishing project
  • Any part of the home has been remodeled or altered since the last test
  • You have long-term plans for selling the home and want to be able to take preemptive action by reducing radon levels
  • The home has a radon mitigation system in place, in which case the radon should be tested every two years

DIY Charcoal Canister Radon Testing Instructions

  1. Close all exterior doors and windows at least 12 hours before starting the test.
  2. Remove the charcoal test sampler from the bag.
  3. Record the start time and date on the data sheet or on the kit.
  4. Place the sampler at the house's lowest level or in the affected room.
  5. Locate the radon sampler around 2 to 7 feet from the floor and at least 3 feet from exterior doors and windows.
  6. Run the test for the allotted time, usually two to seven days.
  7. Stop the test promptly. Record all data on the sampler and data sheet.
  8. Mail the test to the lab within the specified time window, usually around a week to 10 days.

Why It's Important to Test for Radon

Elevated levels of radon can cause lung cancer. Even though smoking is the number one way to contract lung cancer—accounting for 80- to 90-percent of lung cancer deaths—radon is second.

About 21,000 lung cancer deaths per year can be traced to radon exposure. That's more cancer-related deaths than all other types of cancer except for lymphoma and leukemia.

Not only that, but if you smoke, the combined effects of radon exposure and smoking increase the chance of lung cancer tenfold. In other words, 90-percent of the people who contract lung cancer due to radon also smoke.

Safe vs. Unsafe Levels of Radon in the Home

Is any amount of radon in the home safe? Yes, as long as those levels are at or below 4 pCi/L.

Any home that tests at 0.4 to 4 picocuries of radon per liter of air (pCi/L) is generally considered safe. At 4 pCi/L, it's estimated that seven per 1,000 people will contract lung cancer.


It's rare, if not impossible, to find no radon. So, 0.4 pCi/L is considered the base level.

If the levels of radon in your home are above 4 pCi/L, you should take steps to reduce the levels of the gas. At 10 pCi/L, an estimated 18 people per 1,000 will contract lung cancer. At 20 pCi/L, that number doubles.

How to Reduce Radon Levels in the Home

If the radon test shows radon levels of 4 pCi/L or more in your home, there are a number of steps that you can take to reduce the levels of the gas, such as sealing cracks, improving ventilation, and installing a radon mitigation system.

Seal Cracks and Cover Earth

Seal cracks and other openings in the home's foundation. Cover the crawl space with 6 mil plastic sheeting (a plastic 3-inch pipe for passive venting must also be installed).

Improve Ventilation

Improve ventilation by opening windows and doors more frequently. Use kitchen and bath exhaust fans more frequently.

Install a Radon Mitigation System

Install a radon mitigation system, a professionally installed vent pipe that starts at a hole in the foundation and vents outside through the roof

The pipe's start point should be located as close as possible to the source of the radon gas. In most cases, this will be in the basement or crawl space. A fan is typically installed on the vent pipe to help exhaust the radon gas to the outside. 

On average, a professionally installed radon mitigation system will cost from $800 to $1,300.

  • What should you not do during a radon test?

    During a radon test, do not disturb the sampler. Also do not open windows or doors (for short-term tests), turn on fans, use the fireplace or wood stove, or paint or make major remodels to the home.

  • Does opening windows reduce radon?

    Yes, opening windows in your home can help to reduce the levels of radon by increasing ventilation and allowing the gas to dissipate. This is why windows and doors should be kept tightly shut during short-term radon testing: to prevent the radon gas from dissipating.

Article Sources
The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Health Risks of Radon. United States Environmental Protection Agency.

  2. Radon Zones Map. United States Environmental Protection Agency.

  3. Are Granite Countertops Radioactive? Are the Levels Dangerous? United States Environmental Protection Agency.

  4. Radon Test Kits Available for Purchase. National Radon Program Services.

  5. How Often Should I Test/Retest My Home for Radon? United States Environmental Protection Agency.

  6. Health Risks of Radon. United States Environmental Protection Agency.

  7. What Are the Risk Factors for Lung Cancer? Centers for Disease Control and Prevention.

  8. A Citizen's Guide to Radon. United States Environmental Protection Agency.