What Is Radon Testing?

Radon is a radioactive gas that comes from the natural breakdown of uranium in soil, rock, and water. It is invisible, odorless, and tasteless. Radon gets into the air and can enter homes through cracks and openings in the foundation. Exposure to elevated radon levels can increase your risk of developing lung cancer. Radon testing is the process of detecting and measuring radon gas levels in a home or building.

Why Test for Radon?

Radon is the leading cause of lung cancer among non-smokers. The Surgeon General and EPA estimate that radon causes thousands of preventable lung cancer deaths per year. Radon has been found in homes all over the United States. The only way to know if radon is present is to test. Testing is inexpensive and easy. If high levels are detected, steps can be taken to reduce exposure and lower the risk of lung cancer.

Health Risks of Radon Exposure

Prolonged exposure to elevated radon levels can damage lung tissue and lead to lung cancer over time. The longer the exposure and the higher the level, the greater the risk. Radon is estimated to cause approximately 21,000 lung cancer deaths per year in the U.S. among people who have never smoked. For smokers, radon exposure poses an even greater lung cancer risk. Children are also more susceptible to radon risks. Reducing radon levels in homes can help prevent unnecessary lung cancer deaths.

Where Radon Comes From

Radon is a radioactive gas produced by the natural radioactive decay of uranium. Trace amounts of uranium are found in rock, soil, and water. As uranium breaks down, it releases radon gas which seeps up through the ground. Radon gas can enter homes and other buildings through cracks and gaps in the foundation. Any home can have elevated radon levels, regardless of whether it is old or new construction. The only way to know is to test. Geographic location, nearby geology, and construction materials can impact radon levels. The EPA has identified areas with potentially higher radon levels, but any home can have high radon.

Recommended Radon Levels

The Environmental Protection Agency (EPA) recommends taking action to reduce radon levels when the average annual level is 4 pCi/L (picocuries per liter) or higher. There is no known safe level of radon since lung cancer risk increases as radon levels increase. The EPA suggests fixing homes with radon levels at or above 4 pCi/L to reduce the health risk. State radon programs and experts may also recommend fixing homes with levels as low as 2 pCi/L to further reduce risk. Compare your test results to the EPA’s action level of 4 pCi/L and your state’s radon policy.

Types of Radon Tests

There are two main approaches for testing radon: short-term tests and long-term tests. Both test types are relatively easy to use and inexpensive.

Short-Term Radon Test Kits

Short-term tests remain in your home for 2 to 90 days, depending on the device. There are a variety of short-term testing options:

  • Charcoal canisters – Granular charcoal adsorbs radon gas for a minimum of 48 hours before being sent to a lab for analysis.
  • Charcoal liquid scintillation – A small vial with charcoal is analyzed for radon.
  • Alpha track – Small plastic detectors with CR-39 film are left out for several days, then analyzed in a lab.
  • Electret ion chamber – A small chamber containing a device that accumulates and measures radon.
  • Continuous monitor – Electronic testing device continuously samples and records radon levels for up to 1 week.

Short-term tests give you a quick snapshot of your home’s radon level during the test period. Because radon levels fluctuate day-to-day and season-to-season, short-term tests are not intended to determine your year-round average radon level. However, they can be used to indicate whether or not you have a radon problem that warrants further testing or mitigation. The EPA recommends follow-up testing before deciding to install a radon mitigation system.

Long-Term Radon Test Kits

Long-term test kits remain in your home for more than 90 days to give you a reading that reflects your home’s year-round average radon level. Long-term testing options include:

  • Alpha track – This detector is left out for a year before being sent to a lab for analysis.
  • Electret ion chamber – The monitor continually samples and records radon levels for a year.
  • Continuous monitor – Electronic radon monitor samples and records levels for 6 months to 1 year.

Long-term kits provide a more complete picture of the home’s typical radon level over different seasons, weather conditions, closed/open windows, etc. Long-term tests give the most meaningful data on which to base mitigation and risk reduction decisions. If your initial short-term test result is high, EPA recommends follow-up testing with a long-term kit.

Where to Place Radon Tests

Proper test placement is important to get meaningful results. Follow these EPA guidelines when placing radon test kits:

Short-Term Test Placement

  • Place detector 2-7 feet above floor in the lowest livable area of home that is used regularly, but not the bathroom or kitchen.
  • Choose a location away from drafts, high humidity, exterior walls, and heat sources.
  • If in a multi-level home, test the lowest level used regularly (such as a basement or first floor).
  • Close windows and doors normally kept open. Only run ventilation systems normally used and at normal rates.
  • Maintain normal living routines throughout the test period.

Long-Term Test Placement

  • Test the lowest livable level of the home that is used regularly.
  • Place the detector 20-48 inches off the floor in a regularly occupied or frequently-used room, away from corners and objects.
  • Close windows and doors normally kept open. Only use ventilation systems normally used and at normal rates.
  • Live normally throughout the entire test period. The goal is to measure “average” exposure under normal living conditions.

When to Test Your Home for Radon

The EPA and radon experts recommend testing at these times:

  • During real estate transactions – Test when buying or selling a home. Radon levels can change between owners.
  • New construction – Test new homes before moving in and again once lived in. Radon levels can vary.
  • Changing weather – Re-test after major storms, seismic activity, or major renovations done below ground level. Changing conditions can affect radon levels.
  • Living space changes – Retest after converting a basement to living space. Newly occupied areas should be checked.
  • Testing every 5-10 years – Radon levels can change over time due to shifts in ground composition. Re-test every 5-10 years.
  • Seasonal testing – Consider testing in both summer and winter, when windows are closed, to determine your home’s year-round average.

Reading Your Radon Test Results

After testing, the radon measurement device is returned to a qualified radon lab for analysis. The lab will report your test results in picocuries per liter (pCi/L). This indicates the amount of radon decay detected in the air.

  • Less than 4 pCi/L – EPA recommendation is to retest every 5-10 years.
  • 4 pCi/L or higher – EPA recommends taking action to reduce radon levels through mitigation.
  • 8 pCi/L or higher – EPA recommends fixing within weeks. Lung cancer risk increases with increased radon exposure.

Compare your test results to your state’s radon policy (if applicable) in addition to EPA guidelines. Consider retesting before making decisions about whether to install a radon mitigation system.

Is DIY Radon Testing Accurate?

Radon test kits purchased from qualified radon measurement service providers will give you reliable results. Look for kits that meet EPA requirements. Using EPA-approved devices and carefully following kit instructions helps ensure accurate readings.

The EPA cautions that unreliable or incorrect results can occur when:

  • Using testing devices not meeting EPA requirements
  • Improper test kit placement and protocols
  • Time length errors – too short or long outside lab parameters
  • Testing in extreme humidity or temperatures
  • Closed-house conditions not met

Consult with your state radon office for advice and approved radon test kits. Carefully read and follow measurement instructions. Use a qualified radon lab and technique best suited to answer your radon question. This helps ensure accurate radon testing results.

Hiring a Certified Radon Tester

You can perform DIY radon testing or hire a certified radon professional. Nationally-certified testers, mitigators, and labs are trained to:

  • Use proper testing devices and protocols
  • Place detectors correctly
  • Conduct closed-house conditions
  • Analyze lab results
  • Make risk reduction recommendations

A certified radon professional can:

  • Recommend the best test kit and protocol for your needs
  • Provide quality-assurance testing services
  • Offer pre-mitigation radon diagnosis
  • Give custom quotes for needed radon mitigation
  • Perform post-mitigation testing to confirm radon reduction

Look for professionals certified through the National Radon Proficiency Program (NRPP) or National Radon Safety Board (NRSB) when hiring radon testers and mitigation contractors.

Radon Testing for Multi-Family Buildings

Radon testing in multifamily apartment buildings, condos, schools, and commercial property requires a different approach than single-family homes. Consult qualified radon professionals for testing large residential or commercial buildings. Key considerations include:

  • Gaining access to ground-contact areas like basements
  • Placing numerous detectors per EPA protocols
  • Maintaining closed-building conditions
  • Ventilation system analysis
  • Evaluating radon risks for occupants and employees
  • Assessing mitigation and retesting needs

All states require radon testing in schools. Many states also now require testing in daycares, universities, government buildings, hospitals, and personal care homes. Contact your state radon office for radon testing laws in public or commercial buildings.

Radon Water Testing

Radon can dissolve into well water as it flows through cracked bedrock and soil. Radon water testing is advised when using well water for drinking, cooking, showering, and other household uses.

Have a state-certified lab test your well water. If results are 4,000 pCi/L or higher, treat the water to reduce radon before consumption or household use. Radon water treatment options include:

  • Granular activated carbon filters
  • Aeration systems
  • Ozone and ultraviolet systems

Radon rarely affects municipal water sources. Talk to your water company if you are on a public water supply. If needed, certified contractors can test household water for radon and install approved point-of-entry and point-of-use radon reduction systems.

FAQs About Radon Testing

What is radon testing?

Radon testing involves using detection devices to measure the amount of radon gas present in a home or building’s indoor air. Testing is the only way to find out your home’s radon levels.

When should I test for radon?

The EPA advises testing all homes below the third floor. Key times to test are:

  • Before buying a new home
  • After moving into a new home
  • Every 2 years
  • After major home renovations
  • After major weather events

Test in the lowest occupied level of the home. Re-test every 5-10 years to monitor changing radon levels.

Where should I place radon detectors?

In the lowest livable space of the home that is used regularly, 2-7 feet above the floor, away from exterior walls, heat sources, humidity, and objects. Follow kit instructions for ideal placement.

How much does radon testing cost?

Radon test kits cost $15-$50 for DIY options. Hiring a certified tester costs $150-$300 for home inspection-style short-term tests. Long-term tests average $150-$200. Prices vary by location and test type.

What are safe radon levels?

The EPA recommends fixing homes with radon at or above 4 pCi/L. There is no known safe radon level, as risk increases starting at 2 pCi/L. Compare results to your state’s action level.

How long does radon testing take?

Short-term tests take 2-90 days. Long-term tests take a minimum of 90 days up to 1 year for best accuracy. Test duration depends on the device. Long-term tests give the most meaningful results.

Can I test for radon myself?

Yes, DIY radon test kits are easy to use. Buy an EPA-approved test kit and carefully follow all instructions for accurate results. Consider hiring a certified radon tester for peace of mind and proper testing.

What do I do if my house has high radon?

If radon is 4 pCi/L or more, install an active radon mitigation system. This uses a fan to vent radon outside before it can enter the home. High radon levels should be lowered within weeks to reduce the risk of lung cancer.


Radon gas threatens the health of families across the U.S. The only way to know your radon risk is to test your home. Radon test kits are inexpensive, easy to use, and give fast results. Follow EPA guidelines and state radon policies when testing and interpreting results. Fix homes testing at or above 4 pCi/L to reduce lung cancer risk. With proper testing and mitigation, radon exposure can be prevented. Protect your family through regular radon testing in your house or building.