Radon: test the lowest room you live in, and fix the house at 4 pCi/L or more

Why test

Radon builds up indoors because the house traps it. Breathing it over years can cause lung cancer, and most people have no symptoms until the cancer is advanced. [S1] [S9]

• About 21,000 deaths a year. EPA estimates radon causes about 21,000 lung cancer deaths in the U.S. each year, about 2,900 of them among people who never smoked. It’s the leading cause of lung cancer among non-smokers and the second leading cause overall. [S4]
• Smoking multiplies it. EPA’s risk table says that if 1,000 people who smoked were exposed to 4 pCi/L over a lifetime, about 62 could get lung cancer; for 1,000 people who never smoked, about 7. [S1] [S4]
• No level is safe. EPA says any radon exposure carries some risk, and lowering a level below 4 pCi/L still lowers it. CDC adds that children may get higher doses than adults at the same level, because they breathe faster. [S1] [S9]

Which homes need a test

Any home can have a radon problem, EPA says: new or old, well sealed or drafty, with or without a basement. Nearly 1 in 15 U.S. homes is estimated to have an elevated level, 4 pCi/L or more. [S1] [S2]

• Below the third floor. EPA and the Surgeon General recommend testing all homes below the third floor. In an apartment or condo, CDC says to test the lowest level within your unit. [S1] [S8]
• Don’t go by the map. EPA’s Map of Radon Zones dates from 1993, and EPA says it shouldn’t be used to decide whether an individual home needs testing. Test no matter where you live. [S6]
• Times to test. CDC lists: if the home has never been tested; when buying or selling; before and after renovations or radon repairs; and before someone starts spending more time in the basement, like turning it into a bedroom or office. [S8]

Getting a kit

You can test yourself or hire a qualified tester. Your state radon office can list qualified testers, and some states offer free or discounted kits. Kits are also sold online and in hardware and home improvement stores. EPA recommends a qualified tester when you’re buying or selling a home. [S7] [S8]

• Short-term tests stay in the home for 2 to 90 days, depending on the device. They’re the quick way to start. [S1] [S8]
• Long-term tests stay for more than 90 days and give a better read of your year-round average. [S1] [S8]
• At least 48 hours. EPA says every radon test should run a minimum of 48 hours, and some devices need longer. [S2] [S3]
• A lab reads most kits. When the test ends, you reseal it and mail it to the lab named on the package. EPA says results usually come back within a few weeks. [S1]

Setting up a short-term test

Follow the instructions that come with your kit. EPA’s general steps: [S1]

1. Shut the house. Close windows and outside doors and keep them closed as much as possible during the test. For a 2 or 3 day test, close them at least 12 hours before you start, too. [S1]
2. Fans: recirculating only. Heating and air conditioning fans that recirculate air can run. Don’t run fans or machines that bring in outside air. Small exhaust fans used briefly are fine. [S1]
3. Skip stormy days. Don’t run a 2 or 3 day test during unusually severe storms or unusually high winds. [S1]
4. Lowest lived-in level. Use the basement if it’s used often; otherwise the first floor. Pick a room you use regularly, like a living room, playroom, den or bedroom, but not the kitchen or a bathroom. [S1]
5. At least 20 inches up. Put the kit where it won’t be disturbed, away from drafts, high heat, high humidity and exterior walls. [S1]
6. Leave it, then mail it. Leave the kit out as long as the package says. Then reseal it and send it to the lab right away. EPA’s buyer’s guide also says to record the stop time and date. [S1] [S2]

Reading the result

Results come in picocuries per liter, pCi/L. EPA puts the average indoor level at about 1.3 pCi/L and outdoor air at about 0.4. Its action level is 4 pCi/L, and it says to consider fixing between 2 and 4. [S5]

1. Step 1: a short-term test. If the result is 4 pCi/L or higher, test again to be sure. [S1]
2. Step 2: follow up. A long-term test gives the better year-round picture; a second short-term test is faster. If the first result was more than twice the action level, above 8 pCi/L, take a second short-term test right away. [S1]
3. Step 3: decide. Fix the home if the long-term result is 4 pCi/L or more. With two short-term tests, consider fixing if their average is 4 or more; the higher the results, the surer you can be. [S1]

Close calls are close: EPA says that if two short-term tests average 4.1 pCi/L, there’s about a 50% chance the year-round average is a bit below 4. If you later start using a lower floor, such as a basement, test again on that floor. [S1]

Fixing a high level

EPA says radon reduction systems work and can cut levels by up to 99%. Most homes can be fixed for about the same cost as other common home repairs, and most can be brought to 2 pCi/L or below. [S1]

• A vent pipe and fan. The usual fix is a soil suction system, also called sub-slab depressurization: a pipe and fan that pull radon from under the house and vent it outside. It doesn’t need major changes to the home, and similar systems work for crawl spaces. [S1] [S2]
• Sealing helps, but isn’t the fix. Sealing cracks makes other methods work better, but EPA doesn’t recommend sealing alone, because it hasn’t been shown to lower radon significantly or consistently. [S2] [S3]
• Hire a qualified contractor. Your state radon office can name qualified or state-certified contractors, and the two private credentialing programs EPA lists, the National Radon Proficiency Program (NRPP) and the National Radon Safety Board (NRSB), keep their own lists. Get references and more than one estimate. If you want to do it yourself, EPA says to contact your state radon office first. [S1] [S7]
• Test again after. EPA’s reduction guide says to test within 30 days of installation, no sooner than 24 hours after the system starts running, ideally with a 2 to 7 day test you or an independent tester runs. [S3]
• Watch the gauge, keep the fan on. An active system needs a warning device, usually a manometer, that you check regularly. EPA says the fan should never be turned off, fans may last five years or more, and you should retest at least every two years. [S1] [S3]

Sealing drafts for winter? Our caulk and weatherstrip guide covers the gaps above ground, and our carbon monoxide alarm guide covers the other indoor gas you can’t smell. A tighter house doesn’t remove radon from below.

If you’re on a well

Soil gas is the main source of radon in homes, but it can also come in through water, EPA says. A water problem is more likely when the source is ground water, such as a private well or a public system that uses ground water. Most of the risk comes from radon released into the air when you shower or use water, not from drinking it. If you’ve found high radon in the air and your water comes from a well, have the water tested too; on a public supply, contact your water supplier. [S1]

Check a result

Pick your number and which kind of test it came from. The answer puts EPA’s steps from this page in one place. Your state radon office and a certified professional still come first. [S1] [S8]

Radon test checklist

Quick answers