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.
- Is radon radioactive?Yes.
- Does radon have a smell?No.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- Can radon come through concrete?Yes.
- Can a house have radon without a basement?Yes.
- 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.
- 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.
- What causes radon in a house?Radon in a house comes from uranium breaking down in the soil and rock beneath it.
- 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.
- 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.
Health and risk9 questions
- Is radon dangerous?Yes.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- How long before you get sick from radon?Radon does not make you feel sick.
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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- Can radon levels change over time?Yes.
- 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.
- 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.
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.
- Should I test for radon?Yes.
- 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.
- 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.
- 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.
- 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.
- Can I test for radon myself?Yes.
- How long does a radon test take?A radon test takes at least 48 hours.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- How do you know if you have radon in the house?Only by testing.
Mitigation systems20 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.
- 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.
- 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.
- 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.
- How much does radon mitigation cost?Public health agencies put a radon mitigation system in an existing home at $500 to $3,500.
- Can radon be removed completely?Not to zero.
- 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.
- How do you install a radon mitigation system in a basement?Have a qualified mitigation contractor install it.
- 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.
- 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.
- 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.
- Would an exhaust fan in a basement reduce radon?Probably not, and it can make things worse.
- 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.
- 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.
- What CFM radon fan do I need?Enough to keep the soil under your slab at lower pressure than the air in the house.
- Can I turn off my radon system?No.
- 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.
- 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.
- Do air purifiers get rid of radon?No.
- Do dehumidifiers reduce radon?No agency radon guidance lists a dehumidifier as a way to lower radon, and EPA's guide to radon reduction names no drying method among its techniques.
Buying and selling7 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.
- 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.
- Does radon testing affect a home sale?It can shape the deal, but rarely ends it.
- 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.
- 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.
- Does a radon mitigation system hurt resale value?We know of no published figure showing that a radon mitigation system lowers resale value.
- Do FHA and VA loans require radon testing?No for a home bought with an FHA-insured mortgage, and no for a VA loan since May 1, 2026, when VA removed its radon topic from its property requirements.
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.
- 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.
- 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.
- 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.
- 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.
- 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.
- How many neutrons does radon have?Radon-222, the most common isotope, has 136 neutrons: its mass number, 222, minus its 86 protons.
- 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.
- 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.
- What is radon used for?Radon has two kinds of use.
- 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.