Is it safe to buy a house that tested high for radon?

The inspection report comes in, and next to "radon" is a number above 4 pCi/L, often in red. If you hoped to close before Thanksgiving, that line can feel like the deal is over. Usually it isn't. Buying a house that tested high for radon can be a sound decision if the problem gets confirmed, fixed and retested. Radon is one of the most fixable problems an inspection can turn up. The real risk comes from living with a high level for years and doing nothing about it.

01Short answer: yes, if you fix it

A high radon result is a reason to negotiate and to plan a fix. It isn't automatically a reason to walk away. According to the U.S. Environmental Protection Agency, some radon reduction systems can cut levels by up to 99%, and most homes can be brought to 2 pCi/L or below.

The danger is real, though. EPA estimates radon causes about 21,000 lung cancer deaths a year in the U.S. That makes it second only to smoking, and about 2,900 of those deaths are in people who never smoked. The harm comes from long-term exposure, which is why a high reading in a house you haven't moved into yet can still be dealt with.

No radon level is officially called "safe." EPA says even levels below 4 pCi/L carry some risk. The goal is to get the number as low as is practical, not just under one line.

02What the number means

Radon is measured in picocuries per liter of air (pCi/L). These are the benchmarks to know:

• 4 pCi/L and above: the action level. The U.S. Surgeon General and EPA advise fixing a home at 4 or higher.
• 2 to 4 pCi/L: EPA suggests considering a fix in this range.
• 1.3 pCi/L: the average indoor level in U.S. homes. Outdoor air averages about 0.4.

EPA estimates that nearly 1 in 15 U.S. homes has an elevated level, so a high result is common.

EPA's risk figures show why the number matters, and why smoking makes it much worse. Here is the estimated number of people out of every 1,000 who would die of lung cancer from lifetime radon exposure at each level:

• At 1.3 pCi/L (average): about 20 smokers vs. about 2 never-smokers
• At 2 pCi/L: about 32 vs. about 4
• At 4 pCi/L: about 62 vs. about 7
• At 8 pCi/L: about 120 vs. about 15
• At 10 pCi/L: about 150 vs. about 18

These figures assume a lifetime of exposure, not the days or weeks of a test. Radon levels also rise and fall with the weather, the season and how the house is used. One short-term test during an inspection is a screening result. It tells you whether to look closer, but it isn't a final verdict on the house.

03Confirm the result before you react

EPA lays out a simple order of steps:

1. Start with a short-term test. These run anywhere from 2 to 90 days. Real estate tests are usually at the short end.
2. If the result is 4 or higher, follow up. Use either a long-term test or a second short-term test.
3. If the first result is above 8 (more than twice the action level), retest right away with another short-term test.
4. If you used two short-term tests, average them. Consider fixing the home if the average is 4 or higher. If the average sits right at the line, say 4.1, EPA notes there's about a 50% chance the year-round average is somewhat below 4. That's another reason to fix and retest instead of arguing over a tenth of a point.

In a real estate deal, EPA says two short-term tests run side by side can be used to decide on a fix. That helps when a closing date doesn't leave time for a long-term test.

How the test is run matters as much as the result:

• Closed-house conditions. Keep windows and outside doors shut during the test. In fall, with the heat on, that's easier to manage. Make sure the seller knows the rules anyway.
• No severe storms. EPA advises against testing during them.
• An independent tester. Buyers often want a test done by someone with no stake in the sale. Your state radon office can help you find a qualified tester.
• The right floor. Test the lowest level you'll actually live on. If you plan to finish the basement as a family room or bedroom, test the basement.

04Negotiating and who pays

Once the result is confirmed, radon becomes a contract issue like any other repair item. EPA advises that the purchase contract spell out:

• Who does the testing, which kind of test, and when
• How test results and testing costs are shared
• When mitigation happens, if it's needed
• Who pays for it

Common outcomes include the seller installing a system before closing, a price reduction, or a credit at closing so you can hire your own contractor. If the seller installs the system, ask for the contractor's name, the post-install test results and the paperwork. If you get a credit instead, you choose the mitigator and control the quality of the work.

Ask the seller for:

• Any past radon test results, with dates and the levels tested
• Records of any existing system: who installed it, when, and any warranty or operating instructions

EPA also advises sellers to test before listing and to keep records of any fix, so these documents may already exist.

Disclosure rules differ by state. As of mid-2024, ten states had radon awareness and notification laws for home sales: Colorado, Delaware, Florida, Illinois, Iowa, Kansas, Minnesota, Montana, New Hampshire and Rhode Island. Under these laws, buyers must be told about radon risk and sellers must disclose prior tests. In Illinois and Kansas, the disclosure applies only if the earlier level was elevated. These are disclosure laws, not testing requirements. State laws change, so check with your state radon office and your agent about the current rules where you're buying.

05What a fix costs and what to expect

The Minnesota Department of Health says a mitigation system generally costs $1,500 to $3,000. EPA's 2025 cost analysis uses about $1,826 (in 2023 dollars) for a typical sub-slab system. That analysis also assumes about $206 a year to operate it, $476 to replace the fan about every 10 years, and $169 for testing. The final price depends on the home's size, foundation and layout. EPA says most homes can be fixed for about the same cost as other common home repairs.

A typical install: the most common setup is a sub-slab system. A pipe runs from under the basement floor or slab, and a fan pulls radon-laden air from the soil and vents it outside above the house, before it can get indoors. Fan-driven systems work better than passive ones. The tradeoff is a slightly higher electric bill and some loss of heated or cooled air, which is part of that yearly operating cost.

What to ask for:

• A monitor or warning device. Most systems include one to show whether the system is working. Check it now and then.
• Permits. Minnesota notes that most installs need an electrical permit and a licensed electrician for the fan wiring. That isn't a do-it-yourself job.
• Paperwork. Get written operating instructions and copies of any warranties.

Testing afterward:

• Retest within 30 days of the install, but no sooner than 24 hours after the fan starts.
• EPA recommends an independent follow-up test, not just the contractor's own reading.
• Retest every two years, and again after major renovations such as finishing a basement.

Hiring a mitigator: get quotes from qualified contractors. Many states require radon professionals to be licensed, certified or registered, and Colorado has passed a law requiring radon professionals to be licensed. Your state radon office can tell you what applies where you live.

06When to call a pro, and when to walk away

Radon mitigation is a job for a qualified or licensed radon contractor, with a licensed electrician handling the wiring. Get at least two estimates and compare the system design, fan, warranty and post-install testing, not just the price. Ask your state radon office how mitigators are licensed or certified in your state.

Consider walking away or renegotiating hard in these cases:

• The seller refuses to test, share records or address a confirmed high result.
• The home has a complicated foundation, such as a mix of slab, crawlspace and basement, and contractors can't give you a clear plan or price.
• The closing timeline leaves no room to confirm the result or get the fix and retest in writing.

Otherwise, a high radon number usually means a few thousand dollars, a fan, and a retest within 30 days.

Sources (9)

• EPA: Health Risk of Radon
• EPA: A Citizen's Guide to Radon (2016)
• EPA: Consumer's Guide to Radon Reduction (2016)
• EPA: Analysis of Benefits and Costs of Radon (2025)
• EPA: Home Buyer's and Seller's Guide to Radon
• Minnesota Department of Health: Radon Mitigation Systems
• AARST: Homebuyer Awareness Notification Law Toolkit (June 2024)
• Colorado General Assembly: SB23-206
• EPA: Local Radon Zones and State Contact Information

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