What Radon Testing Involves and How Long It Takes?

Radon testing involves placing a specialized device in the lowest livable level of your home for a set period of time, and the process typically takes 48 hours to 7 days for a short-term test. According to the U.S. Environmental Protection Agency (EPA), nearly 1 in 15 homes in the United States has a radon level at or above the recommended action level of 4 picocuries per liter (pCi/L). The only way to know if your home has dangerous radon levels is to test for it, because radon is a colorless, odorless, and tasteless gas. This article covers what happens during a radon test, how long the process takes, what can affect results, and what to do if levels come back high. It is written by Alan Redburn, CPI, a Certified Professional Inspector who provides radon testing services across Mid-Missouri.

What Does Radon Testing Involve?

Radon testing involves placing a detection device in the lowest livable area of your home, keeping the house under closed conditions, and collecting the device after the testing period ends. The process is simple and does not require any major preparation on your part.

A certified inspector places the testing device at least 3 feet off the ground in a room where you spend time, such as a basement or ground-floor living area. According to the CDC, the device must be placed in the middle of the room, away from walls, windows, and drafts. The home must stay under closed-house conditions during the test. That means all exterior windows and doors stay shut except for normal entry and exit.

Homeowners in Cuba, Missouri, and surrounding areas in Mid-Missouri often schedule radon testing during a real estate transaction or as part of routine home safety checks. Many families across Rolla, Jefferson City, and Sullivan pair radon testing with a full home inspection to get a complete picture of the property.

Once the test period is over, the inspector picks up the device and reads the results. Professional-grade continuous radon monitors (CRMs) give results right away, showing hourly averages and peak levels. Charcoal test kits need to be sent to a lab, which adds a few extra days. According to the Michigan Department of Environment, Great Lakes, and Energy, CRMs are the most common devices used in real estate transactions because they deliver fast, detailed data.

How Long Does a Radon Test Take To Get Results?

A radon test takes 48 hours to 7 days to get results when using a short-term method, and 90 days or more for a long-term test. According to the CDC, short-term testing can take 2 to 90 days, while long-term testing takes more than 90 days.

For real estate transactions in Mid-Missouri, most inspectors use continuous radon monitors that run for a minimum of 48 hours. These electronic devices record readings every hour and produce a detailed report as soon as the test ends. According to the Colorado Department of Public Health and Environment, the house must be closed for 12 hours before the testing device is activated, and the test itself runs for at least 48 hours.

Homeowners in the Owensville and St. James area who need quick results for a home purchase should plan for roughly 3 days total, which includes the 12-hour pre-closing period and the 48-hour test window. Lab-analyzed charcoal kits take an additional 1 to 3 business days after the lab receives the kit, plus shipping time.

Are 2 Day Radon Tests Accurate?

Yes, 2 day radon tests are accurate enough for an initial screening, but they do not capture seasonal changes the way a long-term test does. According to the Wisconsin Department of Health Services, short-term tests are a quick way to screen your home for radon, while long-term tests lasting at least 91 days give a better estimate of the annual average.

A professional continuous radon monitor running for 48 hours records data every hour, giving a reliable snapshot of current conditions. These devices are calibrated annually and operated by trained professionals. According to the EPA, if a short-term test shows levels at or above 4 pCi/L, a second test should follow to confirm the results.

For home buyers in the Cuba, MO, area who are working on a tight closing deadline, a 48-hour professional test is the standard approach. It gives enough data to make informed decisions during negotiations.

What Is the Best Type of Radon Test?

The best type of radon test is a professional continuous radon monitor (CRM) for short-term screening and an alpha track detector for long-term measurement. According to the Michigan Department of Environment, CRMs are electronic devices that require annual calibration and are used by trained operators, making them the most reliable option for real estate transactions.

There are three main types of radon tests. Charcoal test kits absorb radon gas over 2 to 7 days and must be mailed to a lab. Alpha track detectors measure radon over 30 days to 1 year. CRMs record electronic readings every hour for 48 hours or more and give instant results.

For homeowners in Mid-Missouri who want the most detailed data, a CRM test performed by a certified inspector gives hourly averages, peak levels, and an overall reading. Buyers working with a buyer’s home inspection often choose a CRM test because it fits within the inspection timeline and provides results the same day the device is picked up.

Is a Professional Radon Test Better Than at Home?

Yes, a professional radon test is better than an at-home test because professional devices are more accurate, are calibrated regularly, and follow strict placement protocols. According to the EPA, qualified testers use devices that meet national standards and follow specific guidelines for placement, timing, and closed-house conditions.

DIY charcoal test kits can give a general idea of radon levels, but they are more prone to errors. A kit left in the wrong spot, exposed for too long, or shipped too slowly can produce inaccurate results. According to the Wisconsin Department of Health Services, test kits exposed for too long or not long enough are invalid.

A certified inspector in the Rolla or Union area will place the device in the correct location, verify closed-house conditions, and use tamper-resistant equipment. This level of care matters during a real estate deal where both the buyer and seller need reliable numbers.

What Not To Do During a Radon Test?

What not to do during a radon test includes opening windows, running whole-house fans, moving the testing device, or tampering with the equipment. These actions allow outside air to dilute radon levels and produce false low readings.

According to the CDC, you must keep all exterior windows and doors closed during the test, except for normal entry and exit. You also need to turn off any fans that pull air in from outside. Running a kitchen exhaust fan, bathroom fan, or attic fan during the test can change the air pressure inside the home and throw off the results.

Do not move or disturb the testing device at any point during the test period. Professional CRMs often have anti-tampering features that record if the device was moved. If tampering is detected, the test is considered invalid and must be repeated.

Homeowners in St. Clair and Washington should also avoid running a fireplace or wood stove during the test, as these create strong drafts that pull outside air into the home. Normal use of heating and air conditioning systems is fine.

What Happens if I Open My Windows During a Radon Test?

If you open your windows during a radon test, the results will be inaccurate because fresh outside air dilutes the radon concentration inside the home. The test would need to be repeated under proper closed-house conditions.

According to the Colorado Department of Public Health and Environment, closed building conditions must be maintained starting 12 hours before the test begins and throughout the entire testing period. Opening even one window can lower the indoor radon reading enough to give a false sense of safety.

Professional monitors often track environmental changes like barometric pressure shifts and temperature swings. If a window was opened during the test, the data may show a sudden drop in radon levels, which flags the reading as unreliable.

Can I Do Laundry During a Radon Test?

Yes, you can do laundry during a radon test as long as the dryer does not vent air to the outside through an open window. Normal use of a clothes dryer that vents through a wall duct is fine. However, you should avoid opening any exterior doors or windows more than needed for normal entry and exit.

The key rule is to keep the home under closed-house conditions. Everyday activities like cooking, showering, and doing laundry are allowed. Just make sure exterior openings stay closed.

What Are the First Signs of Radon Exposure?

The first signs of radon exposure do not appear right away, which is what makes radon so dangerous. Radon is an invisible, odorless gas, and there are no immediate symptoms that alert you to its presence. According to the Agency for Toxic Substances and Disease Registry (ATSDR), it takes years of exposure before any health problems become apparent.

Long-term exposure to high radon levels can lead to lung cancer. According to the National Cancer Institute, scientists estimate that 15,000 to 22,000 lung cancer deaths in the United States each year are related to radon. Symptoms of radon-related lung cancer include a persistent cough, shortness of breath, chest pain, and coughing up blood. By the time these symptoms show up, the damage has already been done.

This is why testing is critical. You cannot rely on how you feel to know if radon is in your home. Homeowners in Jefferson City and across Mid-Missouri should test their homes every 2 to 5 years, even if previous results were low. Radon levels can change over time due to shifts in soil conditions, home renovations, and weather patterns.

How Fast Can Radon Make You Sick?

Radon does not make you sick quickly. The health effects of radon exposure develop over years, not days or weeks. According to the EPA, breathing radon over a long period of time increases your risk of lung cancer. There is no safe level of radon exposure, but the risk goes up as the concentration and time of exposure increase.

The EPA estimates that radon causes about 21,000 lung cancer deaths per year in the United States. About 2,900 of these deaths occur among people who have never smoked, according to EPA health risk data. Smokers who are also exposed to high radon levels face a much greater combined risk. The ATSDR reports that the lung cancer risk from radon is 10 to 20 times greater for smokers compared to people who have never smoked.

Where Is the Best Place in the House To Test for Radon?

The best place in the house to test for radon is the lowest livable level, which is usually the basement or ground floor. According to the EPA, radon levels are typically highest in the lowest part of a home, so testing there gives the most useful reading.

Place the testing device in a room where you spend time, like a bedroom, living room, or family room. Avoid testing in kitchens, bathrooms, laundry rooms, closets, or crawl spaces. According to the Michigan Department of Environment, the device should be placed at least 2 to 7 feet off the floor and away from exterior walls, windows, and doors.

Many homes in the Cuba, MO, area have basements, which makes placement straightforward. If the home has a crawl space instead of a basement, the test goes on the ground floor. Even if a basement is unfinished, it should still be tested if a future owner might convert it into living space.

Where in Your House Is Radon Most Likely?

Radon is most likely in the lowest level of your house that is in contact with the ground, such as a basement or a ground-floor room built on a slab. Radon enters through cracks in the foundation, gaps around pipes, sump pump openings, and porous concrete block walls.

According to the EPA, radon moves up through the ground and enters buildings because indoor air pressure is usually lower than the pressure in the soil beneath the foundation. This pressure difference creates a vacuum effect that pulls radon gas inside. Homes with basements tend to have higher radon levels on the lower floor, but radon can be found on any level of a home.

What Time of Year Is Radon Highest?

Radon is highest during the winter months when homes are sealed up tight for heating. According to the Wisconsin Department of Health Services, winter is a good time to test because it is easier to maintain closed building conditions. Doors and windows stay shut naturally, which means the test reflects typical living conditions during the coldest part of the year.

In winter, the temperature difference between indoor and outdoor air is greatest. This increases the pressure differential that pulls radon from the soil into the home. Snow cover and frozen ground can also trap radon in the soil beneath the foundation, pushing more gas upward into the home.

However, you can test for radon at any time of year. Homeowners in Sullivan and Vienna should not wait for winter if they have concerns now. A short-term test during warmer months still provides valuable data, and a follow-up long-term test can capture seasonal fluctuations.

Does Radon Get Worse in Winter?

Yes, radon levels often get worse in winter because homes are closed up and the stack effect, which is the natural upward movement of warm air, pulls more soil gas through the foundation. According to the Colorado Department of Public Health and Environment, long-term tests run during both heating and non-heating seasons give the most complete picture of annual radon levels.

Frozen ground and snow cover reduce the ability of radon to escape from the soil surface. Instead, the gas follows the path of least resistance, which is often through foundation cracks into the warm, low-pressure interior of the home.

Does Radon Get Higher at Night?

Yes, radon levels often get higher at night. This happens because temperature drops at night increase the pressure difference between indoor and outdoor air. Homes are also more tightly sealed at night with doors and windows closed, which reduces ventilation and allows radon to build up.

Professional CRMs record hourly data, so inspectors can see exactly when radon peaks occur. This level of detail helps homeowners and buyers in Mid-Missouri see patterns in their home’s radon behavior over the full test period.

Which Types of Homes Are at Most Risk of Radon Gas?

All types of homes are at risk of radon gas, including new and old homes, well-sealed and drafty homes, and homes with or without basements. According to the EPA, any home can have a radon problem regardless of its age, style, or construction type.

That said, certain features can increase the likelihood of elevated radon. Homes with basements or slab-on-grade foundations have more surface contact with the soil, which gives radon more pathways to enter. Homes built on granite, shale, or phosphate-bearing soils tend to have higher radon potential because these materials contain more uranium.

According to the Missouri Department of Health and Senior Services, radon is present in every county in Missouri, and their residential testing program shows that 1 in 3 homes tested in the state had indoor radon levels that exceeded the EPA action level of 4.0 pCi/L. That makes radon testing especially important for homes across the Mid-Missouri region, including areas around Rolla, Farmington, and Cuba.

Homes that have undergone major renovations, insulation upgrades, or weatherization projects should be retested. Tightening a home’s envelope can reduce air leakage but may also trap more radon inside.

Does Finishing a Basement Help With Radon?

No, finishing a basement does not help with radon and may actually make the problem worse. Adding drywall, flooring, and insulation to a basement makes the space more livable, but it does not block radon gas from entering through the foundation.

In fact, finishing a basement can seal in radon by reducing air circulation in the lower level. According to the CDC, if you plan a major renovation like converting a basement into living space, you should test for radon before starting work. If levels are high, radon-resistant features should be built into the renovation plan.

Homeowners in Lebanon and the surrounding area who plan to finish a basement should schedule a pre-drywall inspection and a radon test before the project is completed.

Does Good Ventilation Reduce Radon?

Good ventilation can temporarily reduce radon levels by diluting the gas with outside air, but it is not a reliable long-term solution. According to the EPA, sealing and ventilation alone have not proven to be effective standalone techniques for radon reduction.

Opening windows may lower radon readings while the windows are open, but levels rise again as soon as the home returns to normal conditions. In cold Missouri winters, keeping windows open is not practical. A proper radon mitigation system is the only proven way to keep levels consistently low.

Does Opening Basement Windows Help With Radon?

Opening basement windows may help reduce radon temporarily by increasing air flow, but it is not a permanent fix. According to the EPA, the recommended solution for homes with radon levels at or above 4 pCi/L is a professionally installed mitigation system, not ventilation alone.

Basement windows are also the worst windows to open during a radon test because they are closest to the ground where radon enters. Opening them during a test will produce an artificially low reading that does not reflect normal living conditions.

How Many Homes Test Positive for Radon?

About 1 in 15 homes across the United States tests positive for radon at or above the EPA action level of 4 pCi/L. According to the ATSDR, approximately 6 million homes in the country have radon levels above this threshold. In Missouri, the numbers are even higher.

Data from the Missouri Department of Health and Senior Services shows that 1 in 3 homes tested in the state exceeded the 4.0 pCi/L action level. According to RadonAway, 97 counties in Missouri fall into EPA Radon Zone 2, which indicates moderate radon risk, and 11 counties are classified as Zone 1, meaning homes in those areas are predicted to test at or above 4 pCi/L.

These numbers show why radon testing matters for every home purchase in Mid-Missouri. Whether you are buying in Cuba, St. Robert, or Waynesville, testing is the only way to know your home’s actual radon levels. Many buyers add radon testing to their standard home inspection to cover all the bases before closing.

How Often Do Homes Fail Radon Tests?

Homes fail radon tests at different rates depending on the region. Nationally, about 1 in 15 homes has radon above 4 pCi/L. In Missouri, about 1 in 3 homes tested exceeds that level, according to the Missouri Department of Health and Senior Services. A home does not technically “fail” a radon test, but a reading above 4 pCi/L means action should be taken to reduce levels.

According to the EPA, the average indoor radon concentration in American homes is about 1.3 pCi/L. Homes that test above 4 pCi/L are recommended for mitigation. Homes between 2 and 4 pCi/L should also consider mitigation, because there is no known safe level of radon exposure.

What Can Throw Off a Radon Test?

Things that can throw off a radon test include open windows, running exhaust fans, moving the test device, weather changes, and testing during unusual conditions like a renovation or construction. Any factor that changes the normal air pressure or ventilation inside the home can produce inaccurate results.

According to the CDC, closed-house conditions must be maintained for at least 12 hours before the test starts and throughout the entire testing period. Running a whole-house fan, opening a fireplace damper, or using a window-mounted air conditioner that brings in outside air can all skew the data.

Extreme weather events like high winds or rapid barometric pressure changes can also affect readings. A professional CRM tracks these variables, so the inspector can account for unusual conditions in the final report. Homeowners in Washington and DeSoto should schedule testing during a period when no major home projects are happening.

What Is the Biggest Source of Radon?

The biggest source of radon is the soil beneath and around a home’s foundation. According to the EPA, radon forms from the natural breakdown of uranium in soil, rock, and water. About 80% of radon in the atmosphere comes from soil, according to research published in the journal Environmental Research.

Radon rises through the soil and enters homes through cracks in basement floors and walls, gaps around service pipes, construction joints, and sump pump openings. The gas can also enter through well water, but airborne radon from soil is the dominant source.

Mid-Missouri’s geology includes areas of limestone, dolomite, and shale, which can contain uranium deposits that produce radon gas. This makes regular testing important for homes across the region, from Farmington to Eureka.

Radon Test Type Comparison Table

Sources: CDC Testing for Radon in Your Home; Michigan Department of Environment, Great Lakes, and Energy; Wisconsin Department of Health Services; Colorado Department of Public Health and Environment.

What Should You Do if Your Home Has High Radon Levels?

If your home has high radon levels, you should hire a certified radon mitigation contractor to install a radon reduction system. According to the EPA, some mitigation systems can reduce radon levels by up to 99%. The most common method is sub-slab depressurization, which involves installing a pipe and fan system that pulls radon gas from beneath the foundation and vents it outside above the roofline.

According to the Missouri Department of Health and Senior Services, the typical cost of radon mitigation for a 2,000-square-foot home is less than $2,500. The National Radon Program Services at Kansas State University reports that the national average for a radon reduction system ranges from $800 to $1,500, depending on the home’s size and design.

After the system is installed, the home should be retested to confirm that levels have dropped below 4 pCi/L. Homeowners in Cuba, MO, and the surrounding area can schedule a re-inspection to verify the system is working correctly.

The EPA’s December 2025 cost-benefit analysis found that testing and mitigating homes above 4 pCi/L delivers a return on investment of up to $15 for every dollar spent, according to the Wisconsin Department of Health Services. That makes radon mitigation one of the most cost-effective home safety improvements available.

Do Air Cleaners Remove Radon?

No, standard air cleaners and air purifiers do not remove radon gas from your home. Air cleaners filter particles from the air, but radon is a gas, and it passes right through most filtration systems. According to the EPA, the only proven way to reduce radon is with a properly designed mitigation system that vents the gas from beneath the foundation to the outside.

Some air filtration systems can capture radon decay products, which are the radioactive particles left behind when radon breaks down. However, removing these particles does not remove the radon gas itself, so the source of the problem remains. A mitigation system is the correct solution.

Does a Gas Detector Detect Radon?

No, a standard gas detector does not detect radon. Natural gas detectors and carbon monoxide detectors are designed to pick up different types of gases and are not sensitive to radon. You need a device specifically designed for radon measurement, such as a charcoal canister, alpha track detector, or continuous radon monitor.

According to the EPA, testing with a radon-specific device is the only way to know if your home has a radon problem. Smoke detectors and CO alarms, while important, cannot identify radon gas at any level.

What Does Radon Smell Like in Your House?

Radon does not smell like anything in your house. It is completely odorless, colorless, and tasteless. According to the EPA, you cannot detect radon with your senses, which is why testing is the only way to know if it is present in your home.

This is one reason many homeowners are unaware of dangerous radon levels in their home. Without a distinct warning sign, radon can build up to harmful concentrations for years without anyone noticing. Regular testing is the only protection.

Frequently Asked Questions

How Often Should You Test Your Home for Radon in Mid-Missouri?

You should test your home for radon in Mid-Missouri every 2 to 5 years. According to the Wisconsin Department of Health Services, you should also retest after any major renovation that affects the foundation, heating, cooling, or weatherization of the home. Homes in Cuba, Rolla, Jefferson City, and surrounding areas sit in a region with moderate to high radon potential, so regular testing is important for long-term safety.

Is Radon Testing Required When Buying a Home in Missouri?

Radon testing is not required by state law when buying a home in Missouri, but it is strongly recommended by the EPA, the U.S. Surgeon General, and home inspection professionals. Most real estate agents in Mid-Missouri advise buyers to include radon testing as part of the home inspection process, especially in areas with higher radon potential. Getting tested before closing gives buyers the information they need to negotiate repairs or credits if levels are elevated.

What Radon Level Is Considered Safe in a Home?

No radon level is considered completely safe. According to the EPA, the action level is 4 pCi/L, and any home at or above that number should be fixed. The EPA also recommends that homeowners consider taking action for levels between 2 and 4 pCi/L. The average indoor radon level in American homes is about 1.3 pCi/L, according to EPA data.

Can Radon Levels Change From Season to Season in Missouri?

Yes, radon levels can change from season to season in Missouri. Levels tend to be higher in winter when homes are sealed and the stack effect is strongest. According to the Colorado Department of Public Health and Environment, long-term tests that include both heating and non-heating seasons give the best picture of annual radon exposure. Homeowners in Sullivan and St. James should keep this in mind when interpreting a single short-term test result.

What Happens if Radon Is Found During a Home Inspection in Mid-Missouri?

If radon is found during a home inspection in Mid-Missouri at levels above 4 pCi/L, the buyer can negotiate with the seller to install a mitigation system or provide a credit at closing to cover the cost. Many real estate contracts in the Cuba and Rolla area include radon contingencies. According to the Missouri Department of Health and Senior Services, mitigation typically costs less than $2,500 for a standard home and can reduce levels by up to 99%, according to the EPA.

Does Radon Only Affect Homes With Basements?

No, radon does not only affect homes with basements. According to the EPA, any home can have a radon problem, including homes built on slabs, homes with crawl spaces, and homes with finished or unfinished basements. Homes in Washington, Farmington, and Eureka should all be tested regardless of their foundation type. Radon enters through any opening where the home contacts the ground.

How Long Does It Take To Fix a Radon Problem After Testing?

It takes about 1 day to fix a radon problem after testing, in most cases. According to the National Radon Program Services at Kansas State University, a qualified contractor can install a mitigation system in a typical single-family home in one day. After installation, you should wait a few months and then retest to confirm the system is working and that radon levels have dropped below 4 pCi/L. Homeowners across Mid-Missouri who need to know their Missouri home inspection requirements should plan for this timeline during the buying process.

Final Thoughts

Radon testing is one of the most important safety steps any homeowner or home buyer can take. The process is simple, the timeline is short, and the results can protect your family’s health for years to come. With 1 in 3 Missouri homes testing above the EPA action level, the risk is real, especially across Mid-Missouri’s radon-prone geology. Whether you are buying your first home in Cuba, selling a property in Rolla, or just want peace of mind in Jefferson City, knowing your radon levels puts you in control.

If you are ready to schedule a radon test or have questions about your home’s air quality, contact ARC Home Inspections today. Our team provides professional radon testing in Missouri with fast, reliable results you can trust. Call 314-948-3058 or visit our website to request an inspection and protect the health of your family.