Radon guide
Radon when you buy or sell a home
EPA and the Surgeon General recommend testing every home below the third floor, and a sale is the moment most people finally do it. A deal also puts two parties around one result, so how the test is run matters as much as the number.
If you are selling
Test before the house goes on the market, in the lowest level that a buyer could use as living space, finished or not. A result at or above 4 pCi/L is EPA's signal to fix the house before it sells. Keep the test report and any mitigation records; a buyer will ask for them.
Expect a request for a fresh test if your result is more than about two years old, if the house was renovated since, if the original test skipped EPA's testing conditions, or if the buyer plans to use a lower floor than the one you tested. Some states and cities also require sellers to disclose radon information.
If you are buying
If the seller already has a result, check when and where it was taken. A recent test from the lowest usable level, with the testing checklist followed, can stand. Otherwise, write the test into the purchase agreement. EPA suggests settling these points in writing:
- Who runs the test and what type of device.
- When it happens, so it fits inside your inspection window.
- How results and costs are shared between buyer and seller.
- Who pays for mitigation if the level comes back at 4 pCi/L or higher, and when it will be done.
EPA leaves who pays for the test and the fix to the agreement between buyer and seller, so it is settled like any other repair found during inspection.
The three testing options for a sale
| Option | How it works | Fix the home if |
|---|---|---|
| Two tests side by side | Two passive short-term devices in the same spot for at least 48 hours | The average is 4 pCi/L or more |
| Two tests in a row | One passive test for at least 48 hours, then an identical one right after in the same place | The average is 4 pCi/L or more |
| Continuous monitor | An active device that records for at least 48 hours | The average is 4 pCi/L or more |
Side-by-side tests give a more precise reading; tests in a row better reflect the season. Your state radon office can help choose.
Keeping the test honest
A sale gives someone a reason to open windows or move the device. EPA lists precautions a qualified tester can use: a device that records radon often enough to show unusual swings, a motion detector that reveals whether the device was moved, a temperature log that hints at opened doors or windows, a barometric pressure log that captures the weather, tamper-proof seals on windows and a signed non-interference agreement from whoever lives in the home.
Should you buy a house that failed a radon test?
A high result describes a fixable problem. Even very high readings come down with a proper system, which usually leaves a house at 2 pCi/L or lower, and EPA likens the price to a routine home repair. The practical step is to get a mitigation quote during the inspection period and settle in the contract who pays and when the follow-up test will be done. See mitigation costs and how the systems work.
Buying a new home
Ask the builder whether radon-resistant construction was used and whether the house has been tested. These passive features are inexpensive to install during construction and make it easier to lower radon later: when a post-move-in test reaches 4 pCi/L, adding a fan to the pipe already in the walls is usually all it takes. Test soon after you move in either way.
Check the radon zone for the county you are buying in on our radon map by state.
Sources: EPA, Home Buyer's and Seller's Guide to Radon (2024); EPA, A Citizen's Guide to Radon (2016). Updated October 2026.