Retesting guide · source-linked
When to Retest for Radon
Learn when to retest for radon after a procedure problem, mitigation, renovation, a move to a lower level, or before a home sale.
Direct answer
Retest when the first procedure cannot be verified, after major renovation or mitigation, when someone begins using a lower level, or when an older result no longer describes the home. Correct the original problem before starting the new test.
Reviewed September 5, 2026. United States federal guidance. Device instructions and applicable state requirements take precedence.
Evidence standard
Built from the official primary guidance linked on this page.
Source check
Reviewed September 5, 2026 · maintained by RadonVerdict.
Retest when the first procedure cannot be supported
A completed short-term record below the device minimum, a long-term record that did not exceed 90 days, incorrect placement, or a disturbed device can all require review. For a transaction test, unconfirmed closed-house conditions are another material gap.
Check the laboratory or device instructions before repeating the exact same setup. The purpose of the new test is to correct the identified problem, not merely produce another number.
Retest after the home or occupancy changes
CDC recommends testing before and after major renovation, especially work intended to reduce radon. It also recommends testing before someone begins spending more time in a basement or lower level.
EPA similarly says to retest when living patterns shift to a lower level. A previous first-floor result does not automatically document a newly occupied basement.
A buyer may reasonably ask for a newer record
EPA says a buyer may ask for a new test if the checklist was not met, the last test is not recent—for example, within two years—the home was altered, or the buyer plans to use a lower level than the one tested.
This is guidance, not a universal disclosure law. State, lender, contract, and professional requirements can differ.
Keep testing in the maintenance record
After mitigation, testing verifies measured performance rather than merely checking whether a fan sounds normal. CDC advises retesting after work, and EPA says it is a good idea to retest a mitigated home at least every two years.
Keep the new result with the system label, prior reports, repairs, and the date of any fan or foundation work.
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Check only what you can confirm. The summary keeps unresolved items visible instead of converting uncertainty into a pass.
Open the full test plannerCommon questions
Quick answers
How often should I retest after mitigation?
EPA says it is a good idea to retest a mitigated home at least every two years, in addition to checking the system warning device regularly.
Should I retest after renovating?
Yes. CDC recommends testing before and after major structural renovation because changes to the home can change radon levels.
Is a two-year-old test still usable for a home sale?
EPA says a buyer may request a new test when the last result is not recent, using within two years as an example. Contract and state requirements may be more specific.
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