A high radon number on an inspection report feels like a reason to walk away. Usually it is not. Radon is common, it is one of the more predictable home problems to fix, and a purchase is the easiest time to get it fixed, because the cost can be negotiated before you own the house.
What the number means
- 4 pCi/L or higher: EPA recommends fixing the home.
- 2 to 4 pCi/L: EPA suggests considering a fix. There is no known safe level of radon, and lower is better.
- Why it matters: EPA estimates radon causes about 21,000 lung cancer deaths a year in the US, making it the second leading cause after smoking. The risk comes from years of exposure, not from a few weeks of touring a house.
See how common high readings are where you are buying on our radon pages by state and county.
Check that the test was valid
Real estate radon tests are short, so conditions matter. Ask the inspector:
- Did the test run at least 48 hours, in the lowest livable level of the house?
- Were windows and outside doors kept closed for 12 hours before and during the test? Open windows can make a result read low; a closed house is the standard.
- Was it a continuous monitor, or two test kits side by side? Either is acceptable for a sale; a continuous monitor also shows the hour-by-hour pattern.
If the test looks sound and the result is over 4, assume it is real. Retesting rarely makes a high number go away.
What to ask the seller for
- Seller installs a system before closing. The cleanest outcome, but the seller picks the installer, so ask for the details below.
- A credit or price reduction so you hire your own installer after closing. You control the quality; get a quote first so you know the number to ask for. Installed cost is typically $800 to $2,500; harder houses cost more.
- An escrow holdback to cover the work if timing is tight. Your agent and lender will know whether this is common in your area.
If the seller installs the system, ask for
- The installer's certification. Many states require a licensed or certified mitigator, and the national certification programs are NRPP and NRSB.
- A post-mitigation test. EPA's guidance is to test no sooner than 24 hours after the system starts and within 30 days.
- The warranty, and whether it transfers to you.
- A visible pressure gauge (usually a U-shaped manometer on the pipe) showing the fan is pulling suction.
After you move in
Test again within the first year, ideally in the heating season, and every two years after that. A continuous radon monitor makes this easy and catches a failed fan early. If levels stay high after mitigation, see radon system troubleshooting.