Reviewed and updated September 13, 2026. This article provides general public-health and referral guidance, not testing, medical, legal or engineering advice.
Start with the post-mitigation test, not the sound of the fan
A common homeowner complaint is simple: the system is installed, the fan is humming, but the radon result is still higher than expected. In Elmira, Horseheads and Corning, the first question should be whether a proper post-mitigation measurement was completed under the right conditions. New York State guidance says a post-mitigation test should be done within 30 days of installation, but no sooner than 24 hours after an active system has been running.
Keep the full test report, not just the number. Record where the device was placed, the test dates, whether closed-house conditions were maintained and whether the system ran continuously. A result that cannot be tied to a valid test window is harder to use for diagnosis.
The manometer tells you about pressure—not radon concentration
Most active systems have a warning device such as a liquid gauge or another indicator that shows whether the fan is creating a pressure difference. That is valuable, but it is not a radon detector. A gauge can look normal while the indoor radon level remains too high because the suction field does not reach every part of the foundation or because another entry zone is not controlled.
If the gauge suddenly changes from its normal operating position, the fan becomes quiet, an alarm activates or piping is damaged, request service. If the warning device looks normal but the radon test is still elevated, the problem may be system design, foundation communication or an untreated zone rather than a simple fan failure.
Mixed foundations and additions can make one suction point insufficient
A house can have a basement under one section, a slab under an addition, a crawlspace elsewhere or foundation walls that do not communicate well below the floor. EPA guidance recognizes that homes with more than one foundation design may need a combination of radon-reduction techniques. The correct number and location of suction points depend on how air moves beneath the structure.
That is why a system that reduces a reading from very high to lower—but still elevated—should not automatically be called a total failure. It may be controlling one area effectively while another area remains a source. A qualified mitigator can use inspection and diagnostic testing to determine whether the existing design needs an additional suction point, crawlspace treatment or another change.
Do not make random changes to chase the monitor
Changing to a larger fan without diagnostics can increase noise and energy use without solving a disconnected foundation area. Permanently sealing a sump or drain without preserving drainage and service access can create water problems. Opening windows can temporarily change indoor concentration but does not show whether the mitigation system is performing as designed.
If the system is new, contact the installer and ask what post-test target, warranty and correction process were included. If the installer is unavailable or the system is older, the radon system repair page explains what information to gather before requesting an evaluation.
A successful correction ends with another measurement
Any meaningful system change should be followed by radon testing. The final proof is not the new fan model, the number of pipes or how strong the suction feels at an opening. It is a properly collected indoor radon result after the system is operating normally.
Keep the original test, system diagram, warranty, repair notes and each follow-up measurement with the house records. For homeowners in Elmira, Horseheads and Corning, that documentation can also make future maintenance and a later home sale much easier to explain.
Sources
Primary guidance used for this article
We use government and public-health sources, distinguish historical datasets from current household measurements, and do not invent local results. Read our editorial policy.