Resources
Radon questions
Each answer starts with a direct response, then the detail, then the source.
What radon is16 questions
- Where does radon come from?Radon comes from uranium, which is present naturally in nearly all rock, soil and water and decays into radium and then into radon gas. Because radon is a gas, it escapes the ground into the air, where it dilutes outdoors but can build up inside buildings that sit on the soil.
- Is radon radioactive?Yes. Radon is a radioactive gas: radon-222, its most common form, gives off an alpha particle and turns into polonium-218, losing half its atoms in about 3.8 days, and the solid decay products that follow are radioactive too, which is why breathing radon is linked to lung cancer.
- Does radon have a smell?No. Radon has no smell, color or taste, so you cannot detect it with your senses, and a musty, damp or rotten-egg smell in a basement is not a sign of radon; a radon test is the only way to know whether a home has a radon problem.
- Does radon gas rise?Radon rises out of the ground into a building's lowest levels, drawn in by lower indoor air pressure, so levels are usually highest in basements and rooms in contact with the ground. It does not stay there: considerable radon can be found above the ground floor, so homes below the third floor should be tested.
- Where is radon found?Radon is found in rock, soil and groundwater across the country, because it forms wherever uranium in the ground breaks down. It is present at low levels outdoors and can build up to much higher levels inside buildings, where it collects instead of dispersing.
- Where is radon most common?Radon is most common where the soil and rock carry more uranium, the areas EPA's Map of Radon Zones marks as highest potential, and indoors it is usually highest in basements and ground-contact rooms. Elevated levels have been found in every state and in all three zones, so any home can have a problem.
- Do all homes have radon?Every home has some radon, because all outdoor and indoor air has some in it; the average indoor level is about 1.3 pCi/L. What differs is the level, and nearly 1 in 15 homes in the United States is estimated to have an elevated level, in every state and in every kind of home.
- Where is radon found in homes?Radon is usually highest in basements, cellars and other living spaces in contact with the ground, where it enters from the soil through cracks and openings in the foundation. Upper floors can have considerable radon too, so test the lowest lived-in level of any home below the third floor.
- How does radon get into a house?Radon gets into a house from the soil beneath it, through openings in contact with the ground: cracks in floors and walls, construction joints, gaps around pipes, sump pits and crawlspaces. The house pulls it in, because the air pressure inside is usually lower than in the soil around the foundation.
- Can radon come through concrete?Yes. Radon gets through a concrete floor or wall by its openings: cracks, the joint where floor meets wall, gaps around pipes, sumps and drains, and the pores and cavities of hollow block walls. The house is at slightly lower pressure than the soil, so it draws radon in through all of them.
- Can a house have radon without a basement?Yes. Radon gets into any building through the parts that touch the ground, so slab-on-grade homes, crawlspace homes and manufactured homes can all have high levels. Any home may have a radon problem, with or without a basement, and a test on the lowest lived-in floor is the only way to know.
- Does radon come from well water?It can: groundwater from wells normally carries more radon than surface water, and some of that radon escapes into the indoor air when the water is used for showers and other household purposes. Radon from the soil is usually a much larger risk than radon from water, though, so the first test is of the air.
- Do granite countertops give off radon?Granite can give off some radon, since any granite can contain uranium, but building materials rarely cause radon problems by themselves, and levels from granite are not typically high. The soil under a house is the principal source of radon in homes, so test the air to know your level.
- What causes radon in a house?Radon in a house comes from uranium breaking down in the soil and rock beneath it. The gas moves up through the ground, and because air pressure inside a home is usually lower than in the soil around the foundation, the house draws it in through cracks and gaps, where it can build up.
- What houses are most at risk for radon?Any house can have high radon: EPA says new and old homes, well-sealed and drafty homes, and homes with or without basements can all have a problem. Risk is greater in areas EPA rates Zone 1, in homes built on uranium-rich soil, and on the lowest floors, but only a test shows a given home's level.
- What state is highest in radon?There is no official ranking of states by measured radon, and the CDC testing figures the site holds are county figures. By EPA's Map of Radon Zones, a prediction, Iowa and North Dakota are the only states with every county in Zone 1, the highest predicted potential, followed by Wyoming, Montana and Colorado.
Health and risk9 questions
- Is radon dangerous?Yes. Radon is a known human carcinogen and, after smoking, the second leading cause of lung cancer in the United States, where EPA estimates it causes about 21,000 lung cancer deaths a year. The danger builds over years of breathing it, rises with the level, and is far greater for people who smoke.
- How does radon affect human health?Breathing radon at home over a long period raises the risk of lung cancer, the one health effect that is established. The risk grows with the radon level and the length of exposure, and it is much higher for people who smoke.
- How does radon cause lung cancer?Radon decays into radioactive particles that, when breathed in, are deposited on the cells lining the airways, where their radiation can damage DNA and lead to lung cancer over many years. Radon is the second leading cause of lung cancer in the United States, and smoking greatly raises the risk.
- What are the symptoms of radon in your home?Radon in a home gives no warning signs: it has no smell, color or taste, and nothing about how a house looks or feels reveals it. Its health effect is lung cancer, which can appear many years after exposure, so a test is the only way to find radon.
- How long is long-term exposure to radon?There is no set number of years: radon's risk builds with both the level and the time spent breathing it, and EPA describes risk as exposure over a lifetime. A long-term radon test is something different, a measurement that stays in the home for more than 90 days.
- Is it safe to live in a house with radon?Every house has some radon, so safety depends on the level: the lower it is, the lower the risk, and even levels below 4 pCi/L pose some risk. A high result is a reason to confirm it and fix the home, not to move out overnight, because the risk builds over years.
- How can you protect yourself from radon?Test your home, because radon cannot be seen, smelled or tasted, and if the level is high, have a trained contractor install a radon reduction system and test again to confirm it worked. Then retest every two years, and if you smoke, stop, since smoking and radon together raise lung cancer risk.
- Is radon gas a myth?No: radon is a real, measurable radioactive gas, and the Surgeon General has warned that it is the second leading cause of lung cancer in the United States; DHHS, the International Agency for Research on Cancer and EPA consider it a human carcinogen. A simple home test shows whether your own air has a problem.
- How long before you get sick from radon?Radon does not make you feel sick. Its known harm is lung cancer, which CDC says takes many years to develop, and EPA says the time between exposure and the onset of the disease may be many years. The risk grows with the level, the time spent in the home and smoking, so lowering it helps whenever you start.
Levels11 questions
- What is a safe level of radon?No level of radon is known to be safe: any exposure carries some risk, and lowering the level lowers the risk. EPA recommends fixing a home at 4 pCi/L, its action level, and considering a fix between 2 and 4 pCi/L, while WHO's reference level is 100 Bq/m3, about 2.7 pCi/L.
- What radon level is dangerous?EPA treats 4 pCi/L as the level at which to fix a home, and recommends considering a fix from 2 to 4 pCi/L, but there is no line where radon turns from safe to dangerous. The risk rises steadily with the level, with the years of exposure, and sharply with smoking.
- According to the EPA, at what level does radon become a health concern requiring mitigation?EPA's action level is 4 pCi/L: at a confirmed result of 4 pCi/L or more, EPA recommends fixing the home, usually with a vent pipe and fan system. Between 2 and 4 pCi/L, EPA recommends considering a fix, and it says any radon exposure carries some risk, so the line is a decision point rather than a safe limit.
- What are normal radon levels?The average indoor radon level is estimated at about 1.3 pCi/L, and outdoor air normally has about 0.4 pCi/L. Homes vary widely around that, nearly 1 in 15 homes in the United States is estimated to have an elevated level, and even levels below 4 pCi/L pose some risk.
- What does 2, 4, 5, 10 pCi/L mean?They are radon results in picocuries per liter of air. 2 pCi/L is where a fix is worth considering, 4 pCi/L is the action level where a fix is recommended, and 5 and 10 pCi/L are above it, so the advice is the same: fix the home. The average home is about 1.3.
- Is a radon level of 5 pCi/L bad?A result of 5 pCi/L is above EPA's 4 pCi/L action level, so plan to fix the home once the number is confirmed, with a followup test if it came from one short-term test. It calls for a planned fix rather than alarm: most homes can be brought to 2 pCi/L or below.
- Is a radon level of 4.1 considered high?Yes, by EPA's measure: 4.1 pCi/L is just above EPA's 4 pCi/L action level, the point at which EPA recommends fixing a home. EPA's Citizen's Guide says short-term results that close to 4 are less definitive, so a follow-up test should confirm it before you decide.
- How do you read a radon test result?Read a radon result in picocuries per liter (pCi/L) against EPA's marks: 4 pCi/L is the action level for fixing a home, and 2 to 4 pCi/L is the range to consider a fix. First check the test was valid, and confirm a high short-term result with a followup test.
- Can radon levels change over time?Yes. Radon levels swing from day to day and season to season with weather, heating and ventilation, and they can change for good when the house changes: after a renovation, settling, new heating or cooling, or a radon fan that stops working. That is why one old test cannot stand in for a current one.
- When are radon levels highest?Radon levels are usually highest in the colder months, when homes are closed up and heated and radon is most likely to be trapped and build up, and on the lowest floors, closest to the ground. Levels also rise and fall from day to day and hour to hour with weather and ventilation.
- What causes radon spikes?Indoor radon varies from hour to hour and day to day with air pressure, ventilation and weather, and a continuous monitor makes those swings visible as spikes. Base decisions on the average over a full test, and if you have a radon system, check that its fan is running.
Testing20 questions
- How do I test for radon?Use a short-term test kit in the lowest lived-in level of your home, or hire a qualified tester: close windows and doors 12 hours before, set the device at least 20 inches off the floor away from drafts, leave it at least 48 hours, then mail it to the lab. A high result gets a follow-up test.
- Should I test for radon?Yes. EPA and the Surgeon General recommend testing every home below the third floor, whatever its age, foundation or location, because radon cannot be seen, smelled or tasted, and a test, which is inexpensive and takes only a few minutes of your time, is the only way to know a home's level.
- Is a radon test required?Testing is recommended for every home below the third floor, but whether it is legally required depends on your state and local rules and on the terms of a home sale. Some states require disclosure of radon information to buyers, specific testing protocols, or licensed radon professionals.
- What is a radon test?A radon test is a small device that samples a building's air for a set time, at least 48 hours, to measure its radon concentration in picocuries per liter. Passive tests, such as charcoal canisters, go to a lab for analysis afterward; active tests, continuous monitors, record radon themselves and report hourly readings and an average.
- What is radon testing?Radon testing is measuring the radon concentration in a building's air over a set period, with a detector that is either analyzed by a laboratory afterward or reports the result itself. It is the only way to know the level in a specific building, because a map or a neighbor's result describes somewhere else.
- What is a radon test kit?A radon test kit is a small, low-cost detector you set out in the lowest lived-in level of your home for a set time, then reseal and mail to a lab, which reports the radon level. Short-term kits stay out two days to 90 days, and long-term kits more than 90 days.
- Can I test for radon myself?Yes. A do-it-yourself kit from a hardware store, online or by mail is the usual first test, and it takes only a few minutes of your time. Place it in the lowest lived-in level, keep the house closed, leave it for the time the kit says, at least 48 hours, then mail it to the lab.
- How long does a radon test take?A radon test takes at least 48 hours. Short-term tests stay in the home from 2 to 90 days, depending on the device, and long-term tests more than 90 days; a lab result then comes back within a few days or weeks of mailing the device.
- How much does a radon test cost?A do-it-yourself radon test kit costs about $10 to $30 in Wisconsin's health department figure and $20 to $30 in Pennsylvania's, and many states give kits away or sell them for less. A professional test costs more: Virginia's health department says it usually costs $100 to $200, depending on the device.
- When should you test for radon?Test now if your home has never been tested, since EPA recommends testing all homes below the third floor. Then test again after moving into a new home, before and after major renovations, within 30 days of installing a radon system and every two years after, and when you buy or sell.
- How often should I test for radon?Test every home at least once, then again when something changes: after a radon fix and at least every two years after that, after major renovations, and when you start living on a lower level. After a low result, you may want to test again sometime in the future.
- Where should a radon test be placed?Place a radon test in the lowest lived-in level of the home, in a room used regularly such as a living room or bedroom, not the kitchen or bathroom. Set it at least 20 inches above the floor where it won't be disturbed, away from drafts, high heat, high humidity and exterior walls.
- Can you be in the house during a radon test?Yes: you can live in the house as usual during a radon test, coming and going through the doors, running heating and air conditioning, and sleeping in the room with the device. Keep windows and outside doors closed, and do not run fans that bring in outside air or disturb the device.
- What can affect a radon test?Open windows, outside air, storms and high winds, the wrong spot, and a disturbed device can all skew a radon test. Closed-house conditions, correct placement in the lowest lived-in level and leaving the device alone for the whole test guard against each one, and a followup test confirms a high result.
- How does humidity affect radon testing?Humidity is a placement rule for radon tests: keep the device away from drafts, high heat, high humidity and exterior walls, and do not test in a bathroom, kitchen, laundry room or other enclosed humid area. Use a regularly used room on the lowest lived-in level instead.
- Can a radon test be manipulated?Yes, a short-term radon test can be thrown off by opening windows, running fans that pull in outside air, or moving the device, but that changes the reading, not the radon. Such interference can invalidate the result and is illegal in some states, and testers use monitors, seals and agreements to detect it.
- Is a radon detector accurate?Yes, a radon test from a qualified laboratory gives a reliable reading when it is used as its instructions say. Most wrong results come from how the test was run, not the device: improper testing may give an inaccurate result, and one short test only captures a few days of a level that changes.
- Do I need a radon test if I don't have a basement?Yes: any home can have a radon problem, with or without a basement, because radon enters through any part of the building in contact with the ground, such as a slab or the floor over a crawlspace. Test in the lowest lived-in level, which without a basement is the first floor.
- How do you test for radon in well water?Test the air first, then, if you have a private well, have the water tested: a sample is collected and sent to a lab that measures its radon, using different devices and procedures from an air test. Your state radon office or the Safe Drinking Water Hotline can point you to a lab.
- How do you know if you have radon in the house?Only by testing. Radon has no color, smell or taste and gives no immediate health symptoms, so a house can have a high level with no sign at all. A short-term or long-term radon test placed in the lowest lived-in level is the only way to know the level in your house.
Mitigation systems19 questions
- How do I reduce radon in my home?To reduce or get rid of radon, the main method is soil suction: a vent pipe and fan that pull radon from beneath the house and vent it outside before it can enter. Confirm a high result first, hire a qualified contractor, and test again after the system is installed.
- What is radon mitigation?Radon mitigation is work that lowers the radon level in a building, usually a vent pipe and fan system that pulls soil gas from under the home and releases it outdoors before it can enter. A qualified contractor designs it for the foundation, and a follow-up test confirms that it worked.
- What is a radon mitigation system?A radon mitigation system is a permanent installation, usually a vent pipe and a fan that runs all the time, that pulls radon-laden soil gas from beneath a house and releases it outdoors above the roof before it can get in. It is designed for the building's foundation, and a follow-up test shows whether it lowered the level.
- Does radon mitigation work?Yes: some radon mitigation systems can cut the radon level in a home by up to 99 percent, and most homes can be brought to 2 pCi/L or below. The proof for your home is a follow-up test within 30 days of installation, with the fan running continuously after that.
- How much does radon mitigation cost?Public health agencies put a radon mitigation system in an existing home at $500 to $3,500. EPA's range for retrofitting an existing home is $800 to $2,500, and state health departments give ranges such as Wisconsin's $1,000 to $2,000 and Minnesota's $1,500 to $3,000.
- Can radon be removed completely?Not to zero. Outdoor air holds about 0.4 pCi/L, and the ground under a home keeps producing radon. What a radon system can do is cut indoor levels by up to 99 percent, and most homes can be brought to 2 pCi/L or below. A test after the work shows how much was removed.
- How do you reduce radon gas in a basement?The standard way to reduce radon in a basement is soil suction: a vent pipe and fan pull radon from beneath the floor and release it outdoors before it can get in, typically cutting levels by 50 to 99 percent. Sealing cracks helps that system work, but sealing alone is not recommended.
- How do you install a radon mitigation system in a basement?Have a qualified mitigation contractor install it. The contractor puts one or more suction pipes through the basement slab, connects a radon vent fan outside the living space that runs continuously and vents above the roof, seals cracks, fits a warning device, and then a follow-up test within 30 days confirms the level came down.
- How do you install a radon system in new construction?In new construction, radon-resistant features go in with the foundation: a gravel layer under the slab, plastic sheeting over it, sealed cracks and openings, a vent pipe from the gravel to the roof, and an attic junction box. The pipe works passively, and a fan is added if a test after move-in shows radon is still high.
- Can you do radon mitigation yourself?You can install a radon system yourself, but a trained contractor is recommended, because lowering high radon levels takes technical knowledge and special skills, and done wrong it can even raise the level. If you go ahead, first contact your state radon office, and test after the system is running.
- How do you seal cracks in a basement floor for radon?Seal cracks in the floor and walls, floor-wall joints and gaps around pipes with plaster, caulk or other materials made for the purpose, then test again. Sealing is a basic part of most radon fixes, but on its own it has not been shown to lower radon significantly or consistently.
- Would an exhaust fan in a basement reduce radon?Probably not, and it can make things worse. An exhaust fan pushes basement air outdoors, and the make-up air that replaces it can pull more soil gas, and radon, in through the foundation. The fan that does work is a radon mitigation fan, which draws radon from under the slab and vents it above the roof.
- Does opening windows reduce radon?Opening windows can lower radon for a while, because outdoor air dilutes the radon indoors, but it is only temporary: once the windows are closed, levels most often return to where they were within about 12 hours. It costs heated or cooled air and is not considered radon mitigation.
- What filters radon?For radon in indoor air, the recommended fix is not a filter: it keeps radon out, usually with a vent pipe and fan that pull it from under the house. For radon in well water, point-of-entry treatment works: a granular activated carbon filter typically removes 85 to 95 percent and aeration 95 to 99 percent.
- What CFM radon fan do I need?Enough to keep the soil under your slab at lower pressure than the air in the house. For a typical new home with radon piping, a fan moving 100 cubic feet per minute at one inch of water column should be sufficient, but soil, suction points and foundation decide the right fan for yours.
- Can I turn off my radon system?No. A radon fan should never be turned off: it must run continuously for the system to work. The fan draws radon from under the floor and vents it above the roof, and when a system stops venting, radon levels in the building rise. Running it only slightly raises the electric bill.
- How long after radon mitigation can you retest?Wait at least 24 hours after the system starts running with its fan on, and test within 30 days of installation. A test of two to seven days is recommended, with windows and doors closed from 12 hours before. After that, retest at least every two years and after any remodel.
- How do you get radon out of water?Radon is removed from water with point-of-entry treatment, which treats all the water before it reaches the taps, usually by aeration, which typically removes 95 to 99 percent, or a granular activated carbon filter, which typically removes 85 to 95 percent. A filter at a single tap does not address radon released into the air.
- Do air purifiers get rid of radon?No. EPA does not recommend air cleaning to reduce the health risks of radon and its decay products, and it says air cleaners without special media such as activated carbon or alumina will not remove radon gas. What lowers radon is a system that keeps it from entering, such as active soil depressurization.
Buying and selling6 questions
- Should I buy a house with radon?You can buy a house with radon: a high level is a problem that can be fixed, usually with a vent pipe and fan system that costs about the same as other common home repairs. Get a valid test before you buy, and agree with the seller on when any fix happens and who pays.
- Should I get a radon test with my home inspection?Yes, unless the house has a recent test you can rely on: if the home has not been tested, have it tested, and a qualified radon tester is very often a home inspector. Ask for the test by name, and schedule it early, since every radon test runs at least 48 hours.
- Does radon testing affect a home sale?It can shape the deal, but rarely ends it. A radon result becomes something buyer and seller negotiate: if levels are high, they discuss the timing and cost of a fix. Where radon problems have been fixed, home sales have not been blocked, and a documented fix can even help the sale.
- Should I buy a home with a radon mitigation system already installed?Yes, it can be a good sign: a system means a radon problem was found and fixed, and where radon problems have been fixed, home sales have not been blocked. Before you buy, ask the seller for the system's paperwork and test results, check the warning device, and test with the fan running.
- Is it hard to sell a house with radon?Radon need not block a sale: where radon problems have been fixed, home sales have not been blocked or frustrated. The hard part is time, so test before you list, fix a high result while you can choose the schedule, and keep the records a buyer will ask for.
- Does a radon mitigation system hurt resale value?We know of no published figure showing that a radon mitigation system lowers resale value. Where radon problems have been fixed, home sales have not been blocked or frustrated, and a working system with test records showing low levels is sometimes a good selling point.
The element11 questions
- What group is radon in on the periodic table?Radon is in group 18, the noble gases, also called the zero group of gases, and in period 6. It is element 86, symbol Rn, a non-metal that sits directly below xenon in the column, with oganesson, element 118, listed after it.
- Is radon a noble gas?Yes: radon is in group 18, the noble gases, with helium, neon, argon, krypton and xenon, and it is the heaviest and densest of them. It is a naturally occurring, radioactive noble gas that is odorless, colorless and tasteless, and it can build up in homes.
- Is radon a metal, nonmetal or metalloid?Radon is a nonmetal: it is classified as a non-metal and belongs to the noble gases, group 18, with element number 86. It is not a metal or a metalloid, and it is a colorless gas at ordinary temperatures, unlike its neighbors polonium, a metalloid, and radium, a metal.
- Is radon heavier than air?Yes: radon is about 7.8 times as dense as nitrogen and 6.8 times as dense as oxygen, and it was the heaviest known gas when first measured in 1908. Even so, it does not stay in the basement: a home's lower air pressure draws it in, and it reaches upper floors too.
- What is the atomic mass of radon?Radon's atomic mass is about 222: it is listed as 222.01758 in the periodic table and written [222] as its atomic weight. Those figures follow radon-222, the most common and most stable of radon's 39 known isotopes, whose own isotopic mass is 222.017576017.
- How many protons and electrons does radon have?Radon has 86 protons, because its atomic number is 86, and every radon isotope shares that count. A neutral radon atom also has 86 electrons, one for each proton, arranged as [Xe] 6s2 4f14 5d10 6p6 with eight in the outer shell, while the neutron count varies by isotope: radon-222 has 136.
- How many neutrons does radon have?Radon-222, the most common isotope, has 136 neutrons: its mass number, 222, minus its 86 protons. Other isotopes have different counts: radon-220, for example, has 134, and thirty-nine radon isotopes are known in all, each with the same 86 protons but its own neutron count.
- How many valence electrons does radon have?Radon has 8 valence electrons, the 6s2 and 6p6 electrons in its outermost shell, out of 86 electrons in all. Radon is a noble gas with that full outer shell, and it is essentially inert, though fluorine has been reported to react with it to form radon fluoride.
- Why don't radon and krypton bond easily?Radon and krypton do not bond easily because each has a full outer shell of eight valence electrons, 6s2 6p6 for radon and 4s2 4p6 for krypton, leaving little tendency to gain, lose or share electrons. Both are noble gases in group 18, though radon is not completely unreactive: fluorine has been reported to react with it.
- What is radon used for?Radon has two kinds of use. It was once sealed in tiny tubes, called seeds, to treat cancer, a practice now largely discontinued, and scientists use it as a natural tracer to follow groundwater into streams, date groundwater and study how gases move underground and in the air.
- When was radon discovered?Radon was discovered in 1900 by the German chemist Friedrich Ernst Dorn, who found it while studying radium's decay chain and called it radium emanation. Ramsay and Gray isolated it in 1908 and named it niton, and it has been called radon since 1923.