Short-Term vs. Long-Term Radon Testing: Which Is Right for You?

Both short-term and long-term radon tests give you useful data, but they're suited to different situations. Here's how to decide which makes sense for your home.

Illinois lists several approved measurement categories. Short-term options include passive devices such as charcoal or electret detectors and active continuous radon monitors. Long-term options include alpha-track detectors and some electret devices. The right method depends on the reason for testing, and a continuous monitor is read differently from passive devices that require separate analysis.

Real Estate Considerations

Illinois has a specific protocol for time-limited real-estate measurements. Under Appendix B of 32 Ill. Adm. Code Part 422, the minimum test length is 48 hours. The two listed methods are two short-term devices placed side by side and run at the same time, or a continuous monitor that records in hourly increments. Testing is performed in each lowest structural area suitable for occupancy, which can mean more than one location when a home has a basement, crawlspace, or slab section.

IEMA-OHS strongly recommends that every homebuyer have a radon test done before purchase or occupancy. Illinois also sets a specific real-estate testing protocol, which is why many buyers use a licensed measurement professional for a transaction. If you hire someone to measure radon, verify an active Illinois measurement license; measurement and mitigation are separate licenses. The Illinois Radon Awareness Act also requires most sellers to give buyers the state-approved pamphlet and disclosure form and to provide known elevated test results in their possession. The law does not require a seller to perform a new test or mitigation simply because the home is being sold.

After a Short-Term Test Shows Elevation

First identify which testing path applies. For an initial homeowner test outside a sale, Illinois Appendix A calls for a follow-up short-term or long-term measurement when the initial short-term result is elevated, with the exact next step depending on the result. For a valid real-estate measurement, Appendix B says to fix the home when the result is 4.0 pCi/L or higher. A licensed measurement professional can help if the device, placement, weather, or closed-building conditions raise questions about validity.

EPA recommends fixing a home at 4.0 pCi/L or higher and considering a fix between 2.0 and 4.0 pCi/L. Once the applicable testing process supports mitigation, a licensed mitigation professional evaluates the result together with the home’s foundation and layout before designing the system.