Post-mitigation retest

A system indicator can show whether a fan is operating, but a radon test is needed to measure the result. Agree on both the early check and long-term follow-up test before installation.

Health Canada recommends a short-term check by a certified professional after activation to confirm early system performance. The result does not replace a long-term test during the first heating season after installation.

Step two: the long-term test in the next heating season. Health Canada's measurement guide is clear that the real confirmation is a long-term measurement of at least 91 days, run during the heating season after the system goes in, with the detector in the same spot as the original where possible (Guide for radon measurements in residential dwellings). That is the number that goes in the file, goes to a future buyer, and tells you whether you are under 200 Bq/m3 as an annual average rather than on one mild week in April.

Health Canada recommends retesting a home with an active mitigation system every five years. Retest sooner when changes to the home or system could affect radon levels; consult the measurement guide for specific situations.

Health Canada recommends that the post-mitigation test be performed by someone other than the installing company to avoid a conflict of interest. Ask a C-NRPP certified measurement professional about the short check and long-term confirmation.

How long it takes. A short check may indicate early system function. A long-term retest requires at least 91 days during the heating season; lab processing and provider scheduling vary. Ask when results should be available.

Costs vary with the property, testing method, system design and provider. Ask for a current itemized quote and confirm what testing and follow-up are included.

A representative long-term retest below 200 Bq/m³ is below the Canadian guideline for the tested location. Radon risk is not zero below that level. If the result remains above the guideline, ask a certified mitigator to assess the system and propose corrective work.

Arrange a long-term follow-up test during the first heating season after installation. Ask who provides it and who will review the result. Also ask how the exhaust will be kept clear during winter.

What to ask before you sign off the install. Is a post-installation test included. Who supplies the long-term retest kit and when. If the 91-day retest comes back above 200 Bq/m3, what happens and at whose cost. Will you give me a written report with the dates, the location and the lab name on it. How long is the warranty, and does it cover a retest failure rather than only a broken fan.

Keep the original test result, installation details and post-mitigation results together. They can help future owners or service providers understand the system and its measured performance.

A retest estimates the radon level at the measured location over the test period. If the use of lower rooms changes, or the system indicator suggests a fault, seek advice about further testing and system service.