Radon Testing: What Radon Is, Symptoms, Safe Levels and How to Test Your Home

You can't see it. You can't smell it. You can't taste it. It seeps up from the ground into ordinary homes in every single state, old houses and brand-new builds alike. And most people have never tested for it.

Radon is one of the most serious home health risks in the US, and also one of the easiest and cheapest to check. A simple test kit costs about the same as a takeout pizza and could protect your family's lungs for decades. Here's everything you need to know.

What is radon?

Radon is a radioactive gas that forms naturally when uranium in soil, rock and water breaks down. Outdoors, it disperses harmlessly into the air. But it can enter buildings through:

• Cracks in foundations, floors and walls
• Gaps around pipes, wires and drains
• Sump pits
• Crawl spaces
• Construction joints
• Well water, in some areas

Once inside, it can build up to unhealthy levels, especially in basements and lower floors.

Any home can have high radon: old or new, drafty or well-sealed, with or without a basement. Two houses right next door to each other can have very different levels. The only way to know is to test.

Why radon is dangerous

According to the US Environmental Protection Agency (EPA), radon is the second leading cause of lung cancer in the US after smoking, and the leading cause among people who have never smoked. The EPA estimates radon is responsible for about 21,000 lung cancer deaths a year.

When you breathe in radon, it breaks down into tiny radioactive particles that lodge in your lungs. Over years, the radiation they give off can damage lung cells and lead to cancer.

The risk comes from long-term exposure. And smoking and radon together are especially dangerous: the combination raises lung cancer risk much more than either alone.

Radon symptoms: are there any?

No. That's what makes radon so sneaky. There are no immediate symptoms of radon exposure. No headache, no cough, no smell. The first sign may be lung cancer itself, years or decades later. That's why testing matters so much.

How common is high radon?

The EPA estimates nearly 1 in 15 US homes has radon levels at or above its recommended action level. Some regions have much higher rates. The EPA's radon zone map shows areas with higher average potential, but homes with high radon have been found in every state, so every home should be tested regardless of zone.

What is a safe radon level?

Radon is measured in picocuries per liter (pCi/L).

• 4 pCi/L or higher: the EPA recommends fixing your home.
• Between 2 and 4 pCi/L: the EPA suggests considering a fix.
• Average outdoor level: about 0.4 pCi/L.
• Average indoor level in US homes: about 1.3 pCi/L.

There's no known completely safe level, so lower is always better. The World Health Organization recommends a reference level of 100 becquerels per cubic meter, which is roughly 2.7 pCi/L.

How to test your home for radon

Testing is simple, cheap and takes very little effort.

Short-term radon tests

These stay in your home for 2 to 90 days (most kits are 2 to 4 days). You place the detector in the lowest lived-in level of your home, then mail it to a lab for results. Many hardware stores sell them, and many state radon programs offer free or discounted kits. They're a great first step.

Long-term radon tests

These run for more than 90 days and give a better picture of your year-round average, since radon levels change with the seasons and weather.

Continuous radon monitors

Digital monitors plug in or run on batteries and give ongoing readings. They're handy for tracking changes, though consumer models are less precise than lab tests.

Professional testing

Certified radon measurement professionals can test your home, which is common during real estate transactions.

Tips for an accurate radon test

• Follow the kit instructions closely
• Test in the lowest level you regularly use, such as a basement den or ground-floor bedroom
• Keep windows and outside doors closed as much as possible for 12 hours before and during short-term tests
• Place the detector at least 20 inches above the floor, away from drafts, humidity, kitchens, bathrooms and exterior walls
• Don't test during severe storms or high winds
• Mail the kit promptly after testing

What to do after your radon test

• Below 2 pCi/L: great news. Consider retesting every few years, and after major renovations.
• Between 2 and 4 pCi/L: consider a long-term test or a mitigation system.
• 4 pCi/L or higher on a short-term test: do a second test (short- or long-term) to confirm. If the average is 4 or higher, fix your home.
• Very high results (for example, above 10 pCi/L): follow up quickly.

How to fix high radon: radon mitigation

The most common fix is a radon mitigation system, usually a technique called sub-slab depressurization. A pipe runs from beneath your foundation slab to the outside, and a fan draws radon from under the house and vents it above the roofline before it can get inside.

Other techniques include sealing cracks and openings, sealing crawl spaces with plastic sheeting and improving ventilation. Sealing alone usually isn't enough.

How much does radon mitigation cost?

The EPA estimates most homes can be fixed for about $800 to $2,500, depending on the home's design and the system needed. The fan uses roughly as much electricity as a light bulb.

Choose a qualified contractor

Use a certified radon mitigation contractor. Your state radon office can point you to certified professionals. After installation, test again to make sure it worked, and retest every two years or so.

Radon in well water

If your home uses a private well, radon can also enter through water and be released into the air when you shower, cook or do laundry. The risk from breathing radon released from water is much greater than from drinking it. If you have a well, ask your state radon or drinking water program about testing your water.

Buying or selling a home with radon

Radon testing is often part of home inspections. If you're buying, ask whether the home has been tested and whether there's a mitigation system. If levels are high, you can negotiate for the seller to install one. If you're selling, testing ahead of time avoids surprises. For new homes, ask about radon-resistant new construction features, which are cheap to add during building.

Radon and smokers

If you smoke and live with high radon, your lung cancer risk is dramatically higher. Testing for radon and quitting smoking are two of the best things you can do for your lungs. Free help to quit is available at 1-800-QUIT-NOW.

Lung cancer screening

If you're 50 to 80 years old and have a significant smoking history (20 pack-years, and you currently smoke or quit within the past 15 years), the US Preventive Services Task Force recommends yearly low-dose CT lung cancer screening. Ask your doctor whether it applies to you.

Common radon myths

• "Radon only affects certain regions." High levels have been found in every state.
• "Newer homes don't have radon." New and old homes can both have high radon, unless radon-resistant features were built in.
• "Homes without basements are safe." Homes on slabs and crawl spaces can have high radon too.
• "My neighbor tested low, so I'm fine." Levels can vary dramatically between houses on the same street.
• "Radon testing is complicated and expensive." Most kits are inexpensive and take a few days.
• "Fixing radon is too expensive." Most homes can be fixed for about the cost of other common home repairs.
• "Once I've tested, I'm done forever." Retest after renovations, after a few years and after mitigation.

Frequently asked questions about radon

When is the best time to test for radon?

Any time, but winter is often recommended because homes are closed up and levels tend to be higher. January is National Radon Action Month in the US.

How long does a radon test take?

Most short-term kits take 2 to 4 days of testing, plus a week or two for lab results. Long-term tests run for at least 90 days.

Is radon worse in winter?

Often, yes. Closed windows and the "stack effect" from heating can draw more soil gas into homes in colder months.

Do air purifiers remove radon?

No. Standard air purifiers don't reduce radon gas. Mitigation systems do.

Should apartments be tested for radon?

Lower-floor apartments especially should be tested. Ask your landlord, and check your state's rules.

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