Understanding Radon and Its Risks

Radon is a naturally occurring radioactive gas that forms when uranium in soil, rock, and water decays. Because it is colorless, odorless, and tasteless, it can accumulate inside homes without any obvious warning signs. The primary health concern from prolonged radon exposure is lung cancer; the U.S. Environmental Protection Agency (EPA) estimates that radon causes about 21,000 lung cancer deaths per year in the United States, making it the second leading cause of lung cancer after smoking. The risk is especially high for smokers, but even nonsmokers face significant danger from elevated radon levels.

Radon enters homes through cracks in concrete slabs, gaps around pipes, sump pumps, floor drains, and other openings where the house contacts the soil. Because indoor air pressure is often slightly lower than the pressure in the soil, radon can be drawn into the building through these pathways. Once inside, it can accumulate to dangerous concentrations, especially in lower levels like basements and crawl spaces. The EPA has identified certain geographic areas with higher radon potential, but any home — regardless of location, age, or construction type — can have elevated radon levels. Testing is the only way to know for sure.

The Critical Importance of Testing Before Purchase

Radon testing is not yet a standard requirement in most real estate transactions, but it is a prudent step that can save you from health risks and unexpected expenses. Asking for a radon test as part of your home inspection contingency gives you leverage to negotiate with the seller if high levels are found. In some states, sellers are required to disclose known radon levels, but buyers should never rely solely on disclosure statements. A pre-purchase test provides a current, independent measurement and protects your investment.

If you test after moving in and discover elevated radon, you will have to pay for mitigation out of pocket — typically $800 to $2,500. By testing before closing, you can request that the seller install a mitigation system or lower the purchase price to cover the cost. This upfront due diligence can prevent future health risks and financial burdens. Moreover, knowing the radon level gives you peace of mind and helps you plan any necessary mitigation before you unpack a single box.

Types of Radon Tests Available

Short-Term Tests

Short-term tests remain in the home for 2 to 90 days, with 48-hour to 7-day tests being the most common for real estate transactions. These tests provide a quick snapshot of radon levels, but results can be influenced by weather, ventilation, and occupant behavior. The most common short-term devices are charcoal canisters and liquid scintillation vials. They are inexpensive and widely available at hardware stores or online. For real estate purposes, short-term tests are usually sufficient because they can be completed within the inspection period.

Long-Term Tests

Long-term tests stay in place for more than 90 days and offer a more accurate picture of annual average radon exposure because they capture seasonal variations. These tests are ideal for follow-up verification after mitigation or for homeowners who want a more complete assessment. Alpha-track detectors and electret ion chambers are common long-term devices. For pre-purchase testing, long-term tests are rarely practical because of time constraints, but they can be useful if you plan to occupy the home and want ongoing monitoring.

Continuous Radon Monitors

Continuous radon monitors (CRMs) are electronic devices that measure radon levels in real-time and record data over the test period. They are often used by professional radon testers because they provide hourly readings and can detect variations caused by weather or open windows. CRMs are more expensive than passive test kits but are considered highly reliable. Some home inspectors offering radon testing services use CRMs to provide same-day or next-day results, which can speed up the home-buying process.

Step-by-Step Guide to Conducting a Radon Test for a Home Purchase

To obtain accurate results, follow these detailed steps. Many professionals recommend using a certified radon tester, but if you choose to test yourself, strict adherence to the instructions is critical.

  1. Select a certified test kit. Purchase a test kit that has been listed or approved by a recognized radon program, such as those from the National Radon Program at Kansas State University or state radon offices. Avoid old or expired kits.
  2. Plan the timing. Schedule the test during the due diligence period of the home purchase. Short-term tests should be set up at least 48 hours before the inspection deadline to allow time for lab analysis.
  3. Close windows and doors. For a short-term test, the home must be kept in "closed-house" conditions — all windows and exterior doors closed — for at least 12 hours before the test begins and throughout the test. This prevents outdoor air from diluting indoor radon levels and producing falsely low results.
  4. Place the test device correctly. Set the detector in the lowest livable level of the home (basement or first floor, if no basement). It should be positioned 20 inches to 5 feet above the floor, away from drafts, heat sources (furnace, fireplace, direct sunlight), and high-humidity areas like bathrooms. Do not place it in a kitchen, laundry room, or near an air conditioner vent.
  5. Keep the detector undisturbed. Do not move or touch the device during the test period. Avoid opening windows or using exhaust fans unnecessarily. Normal daily activities are fine, but avoid activities that could interfere, such as operating a clothes dryer on high heat for extended periods without makeup air.
  6. Record start and end times. Note the exact time you open the test package and the exact time you close it. Many kits require you to send this information to the lab.
  7. Package and send. After the test duration (typically 48 to 96 hours), seal the kit according to instructions, place it in the provided envelope, and mail it to the designated laboratory. Do not delay mailing — prolonged storage can affect results.
  8. Wait for results. Most labs return results within a few days via email or postal mail. For real estate transactions, rush analysis is often available for an additional fee.

Interpreting the Test Results

Radon levels are measured in picocuries per liter of air (pCi/L). The EPA has established an action level of 4 pCi/L. If your test result is 4 pCi/L or higher, the agency recommends taking steps to reduce radon levels. However, any level of radon carries some risk; the EPA also suggests considering mitigation for levels between 2 and 4 pCi/L, especially if you plan to occupy the lower floors or have children who spend time in the basement.

When interpreting results, consider the test conditions. Short-term tests taken during unusual weather (e.g., heavy rain, strong winds, or extreme cold) can be skewed. If a short-term test shows elevated levels, the EPA recommends performing a follow-up long-term test or a second short-term test under similar closed-house conditions to confirm. For real estate negotiations, a single short-term test is often accepted, but sellers may request a retest if results seem anomalous.

Be aware that radon levels can fluctuate daily and seasonally. Winter tends to produce higher indoor radon concentrations because homes are closed up and the stack effect draws more soil gas indoors. A test conducted in summer might yield lower readings. If you test during moderate weather, the result may not reflect peak levels. This is why following up after purchase with a long-term test is a wise habit.

What to Do If Radon Levels Are High

If the radon test shows levels at or above 4 pCi/L, you have several options:

  • Negotiate with the seller. Ask the seller to install a radon mitigation system before closing, or request a credit toward the cost of future mitigation. Many successful real estate transactions include radon mitigation contingencies. A typical sub-slab depressurization system costs $800–$1,500, and a credit can be negotiated accordingly.
  • Perform a second test. If the first test used a short-term method, consider a second test with a different device or a longer duration to confirm the results. If levels remain high, proceed with mitigation.
  • Hire a certified radon mitigation contractor. Once you own the home, the most common and effective mitigation approach is active soil depressurization (ASD). This involves running a pipe from beneath the slab or crawl space to a fan that vents radon to the outdoors, typically above the roofline. The system can reduce radon levels by 50% to 99%.
  • Retest after mitigation. After the system is installed, retest to verify that radon levels have dropped below 4 pCi/L. Most mitigation companies guarantee their work and will adjust the system if needed.
  • Seal entry routes. While sealing cracks and openings can help, it is rarely sufficient alone. Mitigation professionals may also recommend sealing as part of a comprehensive approach, but active ventilation is the primary solution.

Choosing a Radon Mitigation Professional

Radon mitigation is a specialized trade that requires knowledge of building science and local codes. Look for professionals who are certified by the National Radon Proficiency Program (NRPP) or National Radon Safety Board (NRSB). Many states also have licensing requirements. When vetting a contractor, ask about their experience with homes similar to yours, request references, and ensure they provide a written estimate and guarantee of post-mitigation radon levels. Avoid contractors who promise to "remove all radon" — the goal is to reduce levels below the action threshold, not to zero.

Before hiring, check the contractor’s certification status and any complaints through your state radon office or the Better Business Bureau. A reputable professional will explain the system design, fan sizing, and possible modifications to your home’s aesthetics. They should also be willing to perform a final retest to confirm effectiveness.

Radon in New Construction

Many homebuyers mistakenly believe that new homes are immune to radon problems. In reality, new construction can have elevated radon due to the natural uranium content in the soil under the foundation. Modern energy-efficient building practices, while excellent for saving energy, can also trap radon indoors by reducing air exchange. Some builders include passive radon-resistant features (like a gravel layer and vent pipe stub) during construction, but these must be activated with a fan if levels are high. If you are buying a new home, ask the builder if radon-resistant construction techniques were used and whether the home has been tested. A pre-purchase test is just as important for a new house as for an existing one.

Additional Resources

For more detailed information, visit these authoritative sources:

Testing for radon before buying a home is one of the most important health decisions you can make during a real estate transaction. A simple, low-cost test can reveal hidden dangers and empower you to negotiate a safer home. Whether you perform the test yourself or hire a certified professional, acting before you purchase ensures that radon does not become an unwelcome surprise in your new home. Take the time to test — your lungs will thank you for decades to come.