Radon Gas: Understanding the Invisible Hazard in Your Home

Radon gas is an invisible intruder in many homes, one that carries significant health implications despite being undetectable by human senses. Every homeowner and homebuyer should be informed about radon – what it is, where it comes from, how we detect it, and how we can protect against it. In the context of home inspections, radon deserves special attention as a leading environmental cause of lung cancer. In this post, we provide a comprehensive overview of radon gas with a formal, educational perspective consistent with professional home inspection insights. We will explore radon’s origin, its health risks (including its status as the second leading cause of lung cancer in the U.S.), the evolution of radon detection technology, differences between DIY test kits and professional monitors, methods for mitigating high radon levels, and the standards and protocols that guide radon testing and mitigation – especially in real estate transactions.

An illustration of how radon gas can seep into a house from the soil. Radon is colorless and odorless, making it impossible to detect without testing.

What Is Radon Gas and Where Does It Come From?

Radon is a naturally occurring radioactive gas that forms when certain common minerals in the earth decay. Specifically, radon is produced by the breakdown of uranium, thorium, and radium in rocks, soil, and groundwater. As these elements undergo radioactive decay deep underground, radon gas is released and can move through pores and cracks in the soil. Because it is chemically inert (a noble gas), radon migrates freely through the ground and can seep upward into the air or into buildings. Importantly, radon has no color, odor, or taste, so it cannot be detected by smell or sight – only specialized testing can reveal its presence.

In outdoor air, radon is usually diluted to very low, harmless concentrations. The average radon level in outdoor air is on the order of 0.4 picocuries per liter (pCi/L) in the U.S., which is a very small amount. However, when radon gas enters an enclosed space like a house, it can accumulate to higher concentrations, especially if ventilation is poor or openings allow continuous entry from the soil. Radon typically enters homes through cracks in foundations, gaps around pipes, crawlspaces, sump pits, or any other openings in contact with the ground. For example, a tiny fissure in a concrete slab or an unsealed crawlspace floor can become a pathway for radon gas to flow into the living space. Over time, radon can build up indoors to levels far above what is found outside.

Geography and soil composition play a big role in how much radon will emerge. Radon is found in all 50 states, but certain regions are prone to higher levels due to local geology. Areas with uranium-rich soils and rocks – for instance, parts of the Midwest and Appalachian regions – tend to have more homes with elevated radon. In the Midwest, including states like Missouri, Kansas, Oklahoma, and Arkansas, the underlying soil and bedrock often contain trace amounts of uranium that generate radon. This means homes in these areas have a higher likelihood of testing high for radon unless properly constructed or mitigated. It’s important to understand that even neighboring homes can have very different radon readings; one house may have low levels while the house next door sits over a pocket of geology that releases more radon. The only way to know is to test each home individually.

Radon Exposure and Health Risks

Radon gas by itself does not cause irritation or noticeable acute symptoms – you can breathe it for years without knowing. But hidden danger lies in its radioactivity. When radon decays, it produces radioactive particles (often called radon decay products or “radon daughters”) that can be inhaled into the lungs. These particles emit alpha radiation that can damage lung tissue at the cellular level. Over a long period of exposure, this damage increases the risk of mutations in lung cells, which can lead to lung cancerg. The most serious health risk associated with chronic radon exposure is lung cancer. In fact, radon is the second leading cause of lung cancer in the United States, behind smoking. The U.S. Environmental Protection Agency (EPA) estimates that about 21,000 lung cancer deaths per year are attributable to radon exposure in homes. To put it another way, aside from tobacco smoke, radon is the top cause of lung cancer – and it is the number one cause among non-smokers.

It often surprises homeowners to learn that an invisible gas seeping from the basement can pose such a serious health threat. Unlike many health hazards, radon doesn’t cause any immediate symptoms or illness that would warn you something is wrong. There is no cough, no asthma attack, no respiratory irritation to signal radon’s presence. Exposure is entirely without obvious effect until the cumulative radiation dose triggers cancer years later. Lung cancer from radon typically develops after 5 to 25 years of exposure. The risk is long-term and insidious – truly an “invisible hazard.” For smokers, the risk is even more severe: tobacco smoke and radon have a synergistic effect. A person who smokes and also lives in a high-radon home is at significantly higher risk (on the order of 10 times greater risk of lung cancer from radon than a non-smoker at the same radon level). The combination of smoking and radon exposure is especially dangerous, which is why smokers are strongly urged to test for and mitigate radon to reduce their cancer risk.

What about other health issues, such as asthma or other respiratory conditions? It’s a common question whether radon might also cause asthma attacks or other lung diseases. According to the EPA and current scientific evidence, lung cancer is the only health effect definitively linked to radon exposure; there is no conclusive evidence that radon causes asthma or other non-cancer respiratory illnesses. Radon does not irritate the airways in the way that smoke or allergens do – it doesn’t cause short-term breathing difficulty or trigger asthma symptoms. Some recent studies have explored potential associations between chronic radon exposure and asthma severity in children, but at this time radon is not recognized as a causative factor for asthma. The main danger of radon lies in its cancer-causing potential after long exposure. In summary, you won’t “feel” radon in your home – no headaches, no wheezing – but it could be silently affecting your lung health over the years. This is why public health authorities emphasize radon testing and mitigation: it’s about preventing a cancer risk that would otherwise go unnoticed until it’s too late.

It’s worth noting that the absence of short-term symptoms means high radon levels in a home can go undetected for decades. Many people diagnosed with radon-related lung cancer never realized their home had excessive radon. The lesson is clear: routine testing is critical. As we will discuss, testing is the only way to know if radon is present at elevated levels and thus the only way to guide any necessary protective actions.

A Brief History of Radon Detection and Awareness

Radon may only have become a household concern in recent decades, but scientists have been aware of radon gas for over a century. The story of radon’s discovery dates back to the early 1900s. In 1899, physicist Ernest Rutherford first observed a radioactive gas being released by radium, and in 1900 German chemist Friedrich Ernst Dorn identified that gas as a new element – radon (initially calling it “radium emanation”). Radon’s peculiar properties (radioactivity, invisibility, and origin from earth materials) intrigued researchers, but for many years it was mainly a scientific curiosity. In the early 20th century, radon was actually used in some medical therapies and products (a practice we now recognize as dangerous). It wasn’t until later that the focus shifted to radon as an environmental health hazard.

Widespread detection of radon in the environment began in the context of uranium mining. In the mid-20th century, health officials noted unusually high rates of lung cancer among miners working in uranium mines. By the 1950s and 1960s, studies confirmed that radon gas accumulating in mines was the culprit – those miners were breathing extremely high concentrations of radon and its decay products. This prompted efforts to measure and limit radon in occupational settings. The U.S. Public Health Service started radon monitoring programs in the late 1950s in the uranium-rich mountains of Colorado, New Mexico, and Utah. By the late 1960s, federal agencies were studying radon levels in mines and formulating safety standards for miners. These early detection efforts used rudimentary instruments – for example, detectors known as “alpha track” film and ionization chambers were employed to gauge radon decay products in mine air.

Ironically, even while radon was being addressed in mines, few people realized that radon could also accumulate in ordinary homes. Radon gas is everywhere underground, not just in uranium mines, and by the 1970s some scientists had begun measuring indoor radon in a few homes and buildings as research. The first detailed indoor radon surveys in the U.S. were conducted in the mid-1970s by the Environmental Measurements Laboratory (then under the U.S. Department of Energy). These studies found that some homes did indeed have elevated radon, but the issue didn’t hit public awareness until the 1980s. A turning point was the famous case of Stanley Watras, an engineer at a Pennsylvania nuclear power plant. In 1984, Mr. Watras set off radiation alarms at work – yet the plant reactor wasn’t fueled, so the source of radiation was a mystery. Investigators discovered that he had been contaminated with radon gas at his home. When they tested his house, the basement radon level was astronomical – over 100,000 Bq/m³ (equivalent to about 2,700 pCi/L), which is hundreds of times higher than any acceptable level. Living in that home, the family was getting a radiation dose comparable to smoking several packs of cigarettes a day. This dramatic discovery in 1984 rang alarm bells: if one home could have such high radon, many others might as well. The Watras incident triggered a nationwide investigation into residential radon. Throughout the late 1980s, tens of thousands of homes were tested across the country, and indeed many were found to have elevated radon concentrations (though not as extreme as the Watras home). Public health agencies realized radon in homes was a widespread problem requiring action.

In response to this growing awareness, the EPA launched the Radon Action Program and issued the first set of consumer guidelines for radon in the late 1980s. The agency distributed millions of “radon test kits” to homeowners in high-risk areas and published “A Citizen’s Guide to Radon” to educate the public. During this period, radon detection technology rapidly advanced. Early home tests often used charcoal canisters – small cans filled with activated charcoal that absorb radon over a few days; the canister would then be sent to a lab for analysis of the radioactivity. Another common device developed was the alpha track detector, a small plastic film that radon decay particles etch tracks onto over time (useful for long-term monitoring). These passive devices were inexpensive and easy for homeowners to deploy. On the professional side, more sophisticated instruments were introduced: continuous radon monitors with electronic sensors that can record radon levels hour by hour. By the 1990s, home inspectors and environmental professionals could use electronic radon monitors to get fast, detailed measurements during real estate transactions. The EPA also established the National Radon Proficiency Program (NRPP) to train and credential radon measurement and mitigation professionals, ensuring they used proper techniques and reliable devices. (This program was later managed by private organizations but remains a cornerstone of professional radon certification today.)

From the late 1980s onward, radon testing became a recommended routine for homes in many parts of the U.S. Some states began requiring radon disclosure during home sales. Public health campaigns during the 1990s and 2000s – often declaring January as “Radon Action Month” – further spread the message about testing and fixing homes with high radon. Technologically, radon detection has continued to improve. Modern continuous radon monitors are much more compact and precise, often sampling air continuously and even capable of detecting if a test was tampered with (for instance, if windows were opened). Homeowners today can also buy digital radon detectors for continuous at-home monitoring (small electronic devices that give a readout of daily and long-term average radon levels). Laboratories and manufacturers have refined passive test kits to be quite accurate when used correctly.

What was once an obscure scientific phenomenon is now a standard item on a home safety checklist. Current recommendations (from EPA and state health departments) are that all homes be tested for radon, and if high levels are found, the homeowner should take action to reduce them. The evolution of radon detection – from miners carrying detectors in the 1950s, to a homeowner in 2025 plugging in a digital radon monitor – shows how far we’ve come. Yet the goal remains the same: identify where radon is a problem and address it to protect health.

Radon Testing: Home Test Kits vs. Professional Monitors

If you’re concerned about radon in a home (whether your own or one you plan to buy), the first step is to perform a radon test. There are two general approaches: do-it-yourself radon test kits or professional radon testing services. Both can be effective, but there are important differences in convenience, accuracy, and context of use.

Home radon test kits are widely available and relatively inexpensive. These kits are typically found in hardware stores, home improvement retailers, or can be ordered online. They usually contain a small device that you deploy in your home for a set period. The most common DIY kits are either charcoal adsorption kits or alpha track detectors. A charcoal kit involves exposing a canister of activated charcoal to the air in the lowest lived-in area of your home (often the basement) for a short-term period (usually 2–7 days) under closed-house conditions. During this time, radon in the air adsorbs onto the charcoal. After the exposure, you seal the kit and mail it to a laboratory, which will analyze the charcoal for radioactive decay and report the average radon level during the test period. Alpha track detectors work a bit differently: they contain a special plastic film that is left in place for a long period (often 3 months to a year). As alpha particles from radon decay strike the film, they leave microscopic tracks. The detector is then sent to a lab, where the number of tracks reveals the average radon concentration over the exposure time. Alpha track tests are useful for long-term monitoring to get a true annual average, whereas charcoal kits are useful for quick screening.

The advantages of DIY radon kits are clear – affordability and convenience. A typical kit might cost $20 or less, and you can set it up on your own schedule without needing to arrange an appointment. They are a great initial screening tool to check if your home might have a radon issue. However, there are some limitations. The accuracy of home kits can vary depending on the quality of the device and, critically, how carefully the test instructions are followed. User error is a common issue: if the kit is placed incorrectly or left for the wrong duration, or if closed-house conditions are not maintained (for short-term tests, windows and doors should stay closed as much as possible during the test), the results might not be reliable. Additionally, a mailed-in kit gives you a single average value with no additional context. You won’t get information about fluctuations during the day, and you won’t have an expert on hand immediately to interpret what the number means for your specific situation. If the result comes back borderline or high, homeowners sometimes feel unsure about what to do next or whether the test was done correctly.

Professional radon testing addresses some of these gaps. When you hire a certified radon measurement professional or home inspector to conduct a radon test, they will typically use more advanced equipment and follow established protocols to ensure an accurate result. One common tool is a Continuous Radon Monitor (CRM) – a device with electronic sensors that record radon levels continuously (often hourly) over the test period. These monitors are calibrated instruments, meaning they are regularly tested and adjusted to maintain accuracy, and they often have features to detect tampering or changes in environment (like unexpected temperature swings or power loss) that might invalidate a test. A professional will place the monitor in the appropriate location (usually lowest level of the home that could be used regularly, such as a basement family room) and ensure conditions meet testing standards (e.g., verifying windows are closed and HVAC settings are appropriate). After a 48-hour (or longer) test, the specialist retrieves the device and downloads the data, which can show the variation of radon levels over time in addition to the average. The data might, for example, reveal that radon spiked at night and fell during the day, or it might confirm consistently high readings throughout – this kind of insight is something a single charcoal canister average cannot show. Professional testing tends to be more accurate and comprehensive because of these high-quality instruments and the expertise of the tester. The professional can also analyze and explain the results for you. If a home has a radon level of, say, 5.0 pCi/L (just above the EPA’s action guideline of 4.0 pCi/L), a pro can advise whether immediate mitigation is recommended or if additional confirmatory testing might be warranted. They can also look around the home for clues to radon entry points and suggest next steps.

A professional-grade continuous radon monitor set up on a tripod during a home inspection. These electronic devices record radon levels hourly, providing a detailed picture of radon fluctuations and ensuring a reliable measurement.

The downside to professional testing is cost and logistics. A professional radon test will typically cost more than a DIY kit – often the service ranges from around $100 to a few hundred dollars, depending on the region and whether it’s bundled with a home inspection. You also need to schedule a time for the tester to deploy and later pick up the device, which introduces some inconvenience or waiting. Despite this, many homebuyers opt (or negotiate with sellers) to have a professional radon test conducted during the inspection period of a real estate transaction. In some areas, it’s practically standard to include radon testing in the home inspection process, precisely because buyers want the peace of mind of an accurate reading. In a real estate scenario, time is of the essence – there isn’t time to do a 3-month test. Thus, a 48-hour professional test under closed-house conditions is the norm for transactions, giving a quick snapshot of whether radon is above or below the actionable level.

In summary, home kits are a useful, low-cost screening tool that any homeowner can use to check for radon. They work well when instructions are followed, but they provide limited data and rely on the user to do everything correctly. Professional testing offers a higher level of accuracy and expert interpretation, making it valuable especially when an important decision (like buying a house, or deciding to install a mitigation system) hangs in the balance. For long-term home safety, one strategy might be: use a do-it-yourself kit for an initial check – if the result is safely low, you can re-test every few years or after any major renovations; if the result is elevated or borderline, consider bringing in a professional for a follow-up test and consultation. Both methods have their place, and the good news is that testing has become easier than ever. There’s really no reason for a homeowner to remain in the dark about radon when tests are so readily accessible. The EPA, in fact, urges all homeowners to test, whether using a kit or a professional service, because knowing your home’s radon level is the first step in deciding if you need to act.

Radon Mitigation Systems: How to Reduce Radon Levels

Discovering high radon levels in a home can be unsettling, but the problem is fixable. Over the years, building scientists have developed effective radon mitigation systems that can dramatically lower indoor radon concentrations. The goal of any radon mitigation is straightforward: prevent radon gas from entering the living space, and vent it safely outdoors. The specific techniques to achieve this can vary based on the construction of the house (basement, slab, crawlspace, etc.), but they share common principles.

The most prevalent and reliable radon reduction method is called sub-slab depressurization, a form of active soil depressurization. In a home with a concrete slab foundation or a basement, radon typically enters through the slab/floor. Sub-slab depressurization works by reversing the pressure gradient so that radon-containing soil gas is drawn out from under the house and expelled outside, instead of seeping in. In practice, installing this system involves creating a pathway and suction to actively pull the radon from beneath the foundation. A contractor will typically cut a small hole through the slab (or use an existing opening like a sump pit or drain) and excavate a cavity in the earth below to serve as a collection point (often called a “suction pit”). Into this hole, they will insert a PVC pipe that runs from beneath the slab up to the exterior of the home. Attached to this pipe (usually at attic level or outside the house) is an inline fan – a quiet electric fan designed for continuous operation. When the fan runs, it draws air out from under the slab, creating a lower air pressure in the soil relative to the house. This lower pressure under the house effectively prevents radon-laden soil gas from seeping into the foundation because the airflow is now being controlled and routed through the pipe. Instead, the radon is sucked into the pipe and discharged above the roof line into the outdoor air, where it quickly dilutes to safe concentrations. Active sub-slab suction (depressurization) has proven to be highly effective – it can often reduce radon levels by 90% or more, and typically brings indoor levels down well below the EPA’s action threshold of 4.0 pCi/L. In fact, a properly installed system can usually get levels to 2.0 pCi/L or even lower, though results can vary with home characteristics.

To illustrate, imagine a house with a basement that tested at 8 pCi/L of radon. A mitigation contractor might install one suction point in the basement slab and route the vent pipe up through the house and out the roof (or up the side of the house to above the eaves). The continuously running fan will draw out the radon from under the basement. Post-mitigation tests might then show the home’s radon level has dropped to perhaps 0.5 or 1 pCi/L – a very safe level. This system will run 24/7, usually using only as much electricity as a small bathroom fan. Most radon fans are designed to run for many years (5–15 years is common) before needing replacement, and they are typically about as loud as a quietly humming refrigerator, so they do not significantly disturb home life. Maintenance is minimal, but homeowners should occasionally check that the fan is operating (usually there is a warning device or a u-tube manometer gauge on the pipe indicating suction).

There are several variants of active soil depressurization to accommodate different foundation types. In homes that have a crawlspace (dirt floor), the method is usually called sub-membrane depressurization. The principle is the same – we need to draw the radon out – but because there is no slab, the mitigator lays a thick plastic sheet (membrane) over the entire crawlspace floor, sealing it along the edges and around any piers. Under this membrane, they insert a pipe that connects to a fan, which actively sucks out air from beneath the plastic. The membrane effectively acts like a fake “slab,” trapping the soil gas which the fan then pulls out. This can be very effective at stopping radon from emanating up from an exposed crawlspace soil. Another variant is drain-tile suction. If a house has a perimeter drain tile (a perforated pipe running around the foundation footings to collect water), a mitigator can sometimes tie the radon suction pipe into that drain system. This way, the existing drain network under the slab helps collect radon from around the foundation and the fan draws it out. Similarly, if there is a sump pit for a sump pump, that pit can serve as the radon collection point: the contractor will typically seal the sump with an airtight lid (so it can still function for groundwater, but no air leaks) and then connect the suction pipe to the sealed sump cover. This approach, called sump depressurization, both covers a major radon entry (the sump opening) and uses the sump as a radon suction point. In homes built with hollow concrete block foundation walls, sometimes those blocks can accumulate radon gas. There is a method called block-wall suction that inserts suction pipes directly into the hollow walls to draw out radon before it seeps indoors. All of these techniques are variants of the active depressurization strategy. A professional radon mitigator will evaluate the construction details and choose one or a combination of methods to achieve the best result. In many cases, a single sub-slab suction point is sufficient; in others (large homes or very gravely subsoils), multiple suction points and pipes might be needed to adequately cover the area.

Active mitigation systems are highly effective when properly installed – studies and field experience show reductions in radon of 50% to 99+%, depending on the initial levels and house conditions. The EPA has noted that active sub-slab depressurization is the most common and usually the most reliable radon reduction method for homes. These systems not only reduce radon, but as a side benefit, they can also help vent other soil gases (like moisture vapor or even potentially methane in some areas), improving overall indoor air quality. The continuous airflow from beneath the house can even help dry out a damp basement in some cases.

There are also passive radon control systems, often installed in new construction. A passive radon system is basically the same as an active sub-slab system but without the fan. Builders install a layer of gravel and a vapor barrier under the slab, run a PVC vent pipe up through the house and out the roof during construction, and seal major entry routes. The idea is that natural pressure differentials (warm air rising in the house, etc.) will draw some radon out through this pipe by convection. Passive systems can reduce radon levels to an extent, but if testing later shows the level is still too high, the system is designed so that a fan can be added (activating the system). Many building codes or regulations in high-radon areas now require passive radon systems in new homes. Once the house is lived in, an initial radon test will determine if the passive system is enough; if not, activating it with a fan typically fixes the issue. This approach of “build radon-resistant, then activate if needed” is much easier and cheaper than retrofitting a system after the fact, which is why there are national construction standards (like ASTM E1465 and ANSI/AARST new construction standards) devoted to radon-resistant construction techniques.

For an existing home with elevated radon, installing an active mitigation system is generally considered a straightforward retrofit. It usually takes a qualified radon mitigation contractor a few hours to a day to install, and does not require major alterations to the house. A small hole in the slab, running PVC pipe (often through closets or along an exterior wall), and a fan unit is about the extent of it. The cost for professional radon mitigation typically ranges from around $800 to $1,500, depending on house size and complexity, which is a modest expense relative to the value of cancer risk reduction and peace of mind it provides . After installation, it’s recommended to perform a post-mitigation radon test to confirm the system’s effectiveness. Professionals often guarantee that their system will bring radon below the action level and will make adjustments if the initial installation doesn’t achieve that. Once confirmed, the system should run all the time. Homeowners are advised to re-test for radon every couple of years or at least every five years even with a system in place, just to be sure levels remain low. Additionally, significant changes to the home – like renovations, additions, or alterations to HVAC that might change pressure dynamics – would be a good reason to test again.

In summary, while finding out you have a radon issue can be alarming, the solutions are well-proven. An active sub-slab depressurization system can be thought of as a vacuum that continuously sucks the radon from under your home and ejects it outside, keeping the inside air safe. These systems are quiet, energy-efficient, and very effective at what they do. Thousands of Americans have radon mitigation systems in their homes protecting their families. If your home tests high for radon, a mitigation system is the next prudent step, and it can usually be installed with minimal disruption. By reducing radon levels, you’re effectively removing the lung cancer risk associated with that radon – a substantial health safeguard for you and your family.

Radon Standards and Real Estate Protocols

Because radon is a public health concern that affects homes nationwide, various standards and guidelines have been established to inform and regulate how we measure radon and when to take action. At the federal level, the EPA has set practical benchmarks and recommendations that have been adopted (and sometimes adapted) by states and professional organizations. The most well-known guideline is the EPA’s action level of 4.0 pCi/L. This number is not a magic safety cutoff but rather a guideline for when mitigation is strongly advised. The EPA recommends that if a home’s radon level is 4.0 pCi/L or higher, the homeowners should take action to reduce it. This action level was derived from risk analyses and balancing feasibility – it corresponds to a risk roughly equivalent to smoking a half-pack of cigarettes per day. However, the EPA and other experts also emphasize that no level of radon is completely risk-free, as even concentrations below 4.0 pCi/L carry some risk of lung cancer over long periods. Therefore, the EPA suggests that Americans consider mitigating radon even at levels between 2.0 and 4.0 pCi/L, especially if easy fixes are available. For context, the average indoor radon level in U.S. homes is about 1.3 pCi/L, and the average outdoor level is about 0.4 pCi/L. The long-term national goal (set by Congress in the Indoor Radon Abatement Act of 1988) is that indoor air should be as radon-free as ambient outdoor air, though achieving 0.4 pCi/L in every home isn’t technologically practical in all cases. Nonetheless, many homes can be mitigated to 2.0 pCi/L or below, and it is encouraged to do so if possible, since any incremental reduction in radon reduces risk.

Beyond the EPA guidelines, there are ANSI/AARST national consensus standards that govern radon measurement and mitigation practices. The American Association of Radon Scientists and Technologists (AARST), in conjunction with the American National Standards Institute (ANSI), has produced a series of standards that detail proper procedures for conducting radon tests and installing mitigation systems. For example, ANSI/AARST MAH (Most recent version MAH-2023) is the "Protocol for Conducting Measurements of Radon and Radon Decay Products in Homes." This standard lays out in detail how to do a radon test in a residential setting to ensure consistency and accuracy. It covers things like required test durations, device placement, and conditions (e.g., “closed-building conditions” must be maintained – windows and doors kept closed except normal entry – for at least 12 hours prior to and during a short-term test, to simulate worst-case accumulation). It also addresses how to handle multiple tests or how to interpret results in various scenarios. When you hire a qualified radon professional, they will be following these accepted protocols. Likewise, for mitigation, ANSI/AARST has standards such as ANSI/AARST RMS (Radon Mitigation Standards for existing homes) and CCAH (for new construction radon control). These specify the materials, installation methods, and quality checks for radon reduction systems – from pipe sizing and fan location to post-mitigation testing requirements. For instance, the standards mandate that discharge vents must vent above the roof line and away from windows, that fans should not be inside living spaces, that electrical connections must be to code, and so on. Following these standards ensures that mitigation systems are safe and effective. In fact, many state licensing programs for radon professionals require adherence to ANSI/AARST standards. The National Radon Proficiency Program (NRPP) and the National Radon Safety Board (NRSB) – the two main certification bodies for radon professionals – also base their exams and continuing education on these standards.

Real estate transactions deserve special mention when it comes to radon protocols. When a home is being sold, time is limited and the stakes are high for getting an accurate radon reading. The EPA has a specific guide for buyers and sellers (“Home Buyer’s and Seller’s Guide to Radon”) which distills the protocols into practical advice. Key points include: always test in the lowest level that could be used regularly (even if it’s an unfinished basement, because a buyer might later finish it or someone might sleep in a basement bedroom); for a real estate test, a short-term test of at least 48 hours is usually performed; ensure closed-house conditions starting 12 hours before the test and during the test; if the first test comes out 4.0 pCi/L or above, consider doing a second test to confirm or averaging two short-term tests, unless the first result is significantly high (e.g., above 10, where you might just proceed to fixing it). Many home inspectors who offer radon testing will follow the ANSI/AARST protocols (MAH) which are aligned with these recommendations. In practice, during a home sale, the buyer often requests a radon test. The test device (whether a continuous monitor or two charcoal canisters) will be placed, and a non-interference agreement may be presented to the seller/occupants – this is a document the inspector might ask the seller to sign, promising not to disturb the test or open windows, etc., during the test period, to ensure valid results. After the test, if the result is high, the buyer and seller typically negotiate remediation. In some states, sellers are required to disclose known radon levels or whether a home has a mitigation system. Importantly, if a mitigation system is present, buyers may still test to verify it’s working, and the ANSI standards suggest doing a post-mitigation test within 24 hours to 30 days of installation to verify success – something a new owner would want to know as well.

Various organizations also set radon guidelines. The World Health Organization (WHO), for example, has a recommended reference level of 100 Bq/m³ (about 2.7 pCi/L) for homes, or if not achievable, not exceeding 300 Bq/m³ (8 pCi/L). Some countries use 200 Bq/m³ (5.4 pCi/L) as their action level. In the U.S., the 4.0 pCi/L threshold has become embedded in real estate practice and state health messaging, but there’s a growing trend of “the lower, the better.” The American Lung Association and other health groups echo that radon should ideally be reduced below 2.0 pCi/L if possible, given any excess risk is undesirable.

From a homeowner’s perspective, what matters is knowing the number and knowing what to do. If you test your home and find, say, 3.5 pCi/L, you are below the EPA action level, and you might decide not to mitigate immediately – but you should definitely continue periodic testing, and you might take some easy steps (improve ventilation or seal obvious foundation cracks) to see if you can nudge the level lower. If your home tests at 4.1 pCi/L, that’s essentially the EPA line where you should arrange for mitigation. Certainly, at levels significantly above 4 (e.g., 8 or 10 pCi/L), it’s highly recommended to fix the home. And if you ever see extremely high levels (20, 30 pCi/L or more), you’d want to take action as soon as possible, potentially even relocating for a short time if levels are extraordinarily high, until fixed. Fortunately, such high readings are uncommon, and when they do occur, a mitigation system can usually bring the situation under control quickly.

In real estate deals, the resolution is often straightforward: if radon is high, either the seller will install a mitigation system before closing, or the buyer and seller agree on a credit or escrow for the buyer to install one after closing. Because radon mitigation is well-understood and not prohibitively expensive, it usually doesn’t derail a transaction; it becomes a negotiable item much like replacing an old water heater or repairing a roofing issue. Many buyers specifically ask about radon, and smart sellers preemptively test their home before listing so they can show either “radon is low” or “we installed a mitigation system because it was high, and now it’s low.” This transparency can be a selling point.

To ensure quality, if you are hiring radon professionals, check that they are certified or licensed according to your state’s requirements. Many states have radon certification programs (for example, Illinois and New Jersey require state licensing of radon mitigators and testers). In states without their own program, the NRPP or NRSB certifications are the national credentials to look for. Certified professionals will adhere to the ANSI/AARST standards we discussed and will perform testing and mitigation in line with best practices.

In conclusion, understanding radon gas is crucial for homeowners, homebuyers, and home inspectors alike. Radon is an ever-present natural hazard – an invisible gas from the ground that can accumulate to dangerous levels indoors. It is responsible for thousands of lung cancer deaths each year in the U.S., making it a serious environmental health risk. Yet, this is a risk with a straightforward solution: test and mitigate. With modern knowledge and technology, we can detect radon with reliable methods and reduce it effectively in any building. National standards guide these efforts, ensuring that radon measurement is done accurately and mitigation systems are installed safely. From the initial discovery of radon to the latest digital monitors and mitigation fans, we have turned a hidden danger into a manageable aspect of homeownership. Every informed homeowner should include radon in their home maintenance and health checklist. By testing your home and, if necessary, installing a mitigation system, you can breathe easy knowing that you have protected your indoor environment from this invisible threat. Radon may be colorless, odorless, and silent – but with awareness and action, it need not be deadly. In the realm of home inspections and residential health, addressing radon is a key step toward ensuring a safe and healthy home for you and your family.