RadonPilot

Testing

Post-Mitigation Radon Testing

A radon system is designed to reduce indoor levels. Whether it did — and by how much — is established by measuring afterwards. Without that measurement, an installed system is an assumption with a fan attached.

Why follow-up testing matters

Testing, mitigation and post-mitigation testing workflow1. Test the home2. Interpret result3. Professional evaluation4. Mitigation5. Post-mitigation testRetest periodically
The decision path most homeowners follow: test, interpret the result against published guidance, evaluate mitigation with a certified professional where appropriate, then test again after the system is installed.

A gauge on the pipe shows the fan is producing suction. It does not show what the radon concentration in the living space is. Only a radon measurement does that.

The follow-up test is also the document that matters later: in a future sale, for the contractor's warranty, and as the baseline every subsequent test is compared against.

Timing

Published guidance and standards describe when a verification test should be conducted relative to system start-up, and contractors typically build that timing into their scope. Ask before installation who performs the test, when, and whether it is included in the price.

Timing expectations come from the guidance and standards applicable to your building type and jurisdiction. Confirm the specific timing with your certified professional and current official sources rather than assuming a fixed interval.
Source: US EPA — Consumer's Guide to Radon Reduction · United States · cost-reference · Last verified: verification date not recorded
Source: ANSI/AARST Radon Standards of Practice · United States · regulation · Last verified: verification date not recorded

Test conditions

  • The system must be running normally throughout the test.
  • Closed-building conditions as described in the device instructions and guidance.
  • The device placed on the lowest lived-in level, per published placement guidance.
  • No renovation or foundation work in progress during the measurement.
  • Nothing altering building pressure — window fans, whole-house fans, blower-door work.
  • The device left undisturbed for the full exposure period.

General testing guidance applies here too — the same things that spoil an initial test spoil a verification test.

If the level is still elevated

An elevated verification result is information, not a verdict on the whole approach. Common directions an evaluation takes:

  • Suction may not be reaching the whole foundation area — an additional point may help.
  • Sub-slab material may be less permeable than expected.
  • An untreated foundation zone, such as an addition or a crawl area, may be contributing.
  • Large openings — an unsealed sump, a floor drain, a utility chase — may be short-circuiting the system.
  • Fan selection may not match the measured conditions.

What to do when a system is not performing

Ongoing retesting

Buildings change: renovations, new drainage, a replaced fan, settling and cracking. Periodic retesting is how a mitigated home stays verified rather than assumed. Retest after any work that affects the foundation, the system or the building envelope.

Maintenance checklist

Source: US EPA — A Citizen's Guide to Radon · United States · guidance · Last verified: verification date not recorded

Where to go next

System not workingSymptoms and what they usually indicate.MaintenanceA checklist for an existing system.Fan replacementWhen the fan itself is the question.TransactionsDocumentation buyers and sellers rely on.

Request a post-mitigation test or system evaluation

Share your test result, foundation type and project details. We pass your request to independent radon professionals — we do not perform the work ourselves.

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