Radon Test for Home Inspection
Should you get a radon test during a home inspection? Learn what to request, who conducts the test, what the results mean, and what happens if levels are high.
Yes, you should know the radon level of a home before you buy it. Radon is the second leading cause of lung cancer in the United States, and the only way to know whether a specific home has elevated levels is to measure it. Each test runs for as little as 48 hours, and high results can be addressed before you close.
This guide follows U.S. EPA guidance and its action level of 4 pCi/L (148 Bq/m³). Rules for real-estate radon testing also vary by state, loan program and contract, so check what applies where you are buying.
Why radon testing matters in a real-estate transaction
Radon levels vary significantly from house to house, even in the same neighborhood. A home’s foundation type, soil conditions, and ventilation all affect how much radon enters. A standard home inspection covers structural and mechanical systems; it does not measure radon unless you arrange a radon test. Skipping the test means taking on an unknown health risk — and a potential negotiating cost — after the keys are already yours.
The EPA recommends that buyers know the radon level of any home they consider buying, and that sellers test before putting a home on the market.
How to request a radon test
Radon testing is often ordered together with the home inspection, but booking the test and protecting your rights are two different things. What protects you is your purchase contract. The EPA suggests the contract spell out:
- where the test will be placed, who will conduct it, what type of test to use, and when;
- how the buyer and seller will share the results and any test costs;
- when any radon mitigation will be done, and who will pay for it.
Your right to negotiate or withdraw after a high result depends on your contract and local rules — ask your agent how to word it.
When you arrange the test:
- Use a qualified radon tester. This is very often a home inspector who offers radon testing. Ask about credentials — many states require radon professionals to be licensed, certified or registered — and confirm that the device suits the situation.
- Test in the lowest level that could be used regularly, whether finished or unfinished. An unfinished basement counts, even if no one has decided how to use it yet.
- Keep closed-house conditions. Doors and windows stay shut except for normal entry and exit; for tests shorter than four days, close them at least 12 hours before the test starts.
- Ask how interference will be prevented or detected — for example, a device that records readings frequently, motion sensors, tamper-proof seals on windows, or a non-interference agreement signed by the seller or occupant.
To find a qualified tester in your area, contact your state radon office or search the National Radon Proficiency Program (NRPP) directory.
Choosing a short-term testing option
For a home sale, the EPA describes three short-term options. Each test runs for at least 48 hours, and some devices need longer:
| Option | How it works | When to fix the home |
|---|---|---|
| Passive, simultaneous | Two short-term tests at the same time, in the same location | Average of the two is 4 pCi/L (148 Bq/m³) or higher |
| Passive, back-to-back | One short-term test, then an identical second test in the same location right after | Average of the two is 4 pCi/L (148 Bq/m³) or higher |
| Active | A continuous monitor | Average level is 4 pCi/L (148 Bq/m³) or higher |
Two tests at the same time give a more precise result; two tests in a row better reflect the seasonal average. Your state radon office can help you choose.
Passive devices must be mailed to a lab, so shipping and analysis add to the timeline. Agree on when the report will be delivered before you schedule the test.
What the results mean
Results are reported in picocuries per liter (pCi/L). The EPA action level is 4 pCi/L (148 Bq/m³).
| Result | What it means for the transaction |
|---|---|
| Below 2 pCi/L (74 Bq/m³) | Lower risk, but not zero — the EPA notes that no level of radon is completely safe |
| 2 pCi/L (74 Bq/m³) – 4 pCi/L (148 Bq/m³) | Below the action level; the EPA suggests considering a fix in this range |
| 4 pCi/L (148 Bq/m³) or higher | Fix the home — discuss mitigation before closing or a credit |
Negotiating when levels are high
If the test comes back at 4 pCi/L (148 Bq/m³) or higher, the buyer and seller should discuss the timing and cost of fixing it. Common options:
- Request mitigation before closing. Ask the seller to have a qualified contractor install a radon reduction system — most often sub-slab depressurization. Most homes can be reduced to 2 pCi/L (74 Bq/m³) or below.
- Negotiate a credit. If the seller prefers not to install the system before closing, negotiate a reduction in the purchase price or a closing credit to cover the cost. The EPA says most homes can be fixed for about the same cost as other common home repairs; get estimates from one or more qualified mitigators.
- Withdraw if your contract allows it. Whether you can do this depends on the terms you agreed to.
A radon test result at or above 4 pCi/L (148 Bq/m³) is not a reason to automatically walk away from a home you want. Mitigation is a well-established fix. After the system is installed, an independent, qualified tester should confirm that the level has come down.
What if you’re selling?
The EPA recommends testing before you put the home on the market. Knowing your radon level in advance lets you fix it on your own schedule, rather than scrambling to negotiate after a buyer’s test comes back high. Keep the results and records of any work done.
A buyer may still ask for a new test — for example, if your last test is more than about two years old, you have renovated since, or the buyer plans to use a lower level than the one you tested. If you already have a mitigation system, provide its documentation and make sure the vent fan is running during any test.
A DIY test or continuous monitor is useful for ongoing monitoring after you move in, but a real-estate test should follow the EPA’s real-estate testing options above. Radon testing does not replace a professional home inspection or other due-diligence steps.
Frequently asked questions
Is radon testing required during a home inspection?
Who should conduct the radon test for a real-estate transaction?
What happens if the radon test comes back high?
How long does a radon test take for a home sale?
Sources
- A Citizen's Guide to Radon — U.S. EPA
- Home Buyer's and Seller's Guide to Radon — U.S. EPA
- Find a Radon Test Kit or Measurement and Mitigation Professional — U.S. EPA