What to Expect During a Radon Test

If you've never had your home tested for radon before, the process is simpler than most people expect. Here's a clear walkthrough of what a short-term radon test involves.

What You Need to Do

Your measurement professional or test instructions should control the details. For a test lasting less than 96 hours, Illinois closed-building conditions begin at least 12 hours before placement and continue through the test:

• Keep all windows and exterior doors closed except for normal entry and exit
• Operate permanently installed heating and cooling equipment normally; recirculating air conditioning may run
• Do not use a whole-house fan, and follow the written instructions for dryers, range hoods, and bathroom fans because they can affect results
• Do not operate ceiling fans, portable filters, humidifiers, or dehumidifiers within 20 feet of the device
• Continue normal entry and exit, but do not create extra ventilation
• Do not move the test device

Short tests under 96 hours are not conducted during severe storms or sustained high winds under the Illinois professional protocol. Renovation or HVAC work that changes normal airflow can also invalidate a measurement. A licensed tester may reschedule rather than produce a questionable result.

The Two Types of Tests

There are two broad approaches to residential radon testing: short-term and long-term. Under Illinois rules, a short-term test runs from 2 to 90 days, and most run from 2 to 7 days. A long-term test runs 91 days or more and gives a better estimate of the home's year-round average.

Illinois starts both ordinary homeowner and real-estate testing strategies with a short-term measurement. Real-estate testing has its own rules: a minimum 48-hour test, performed either with two devices side by side at the same time or with a continuous monitor that records hourly readings.

How the Devices Work

Illinois recognizes multiple device categories. Passive devices include activated charcoal, charcoal liquid scintillation, and short-term electret detectors. Active continuous radon monitors use power and record readings at least hourly. Some passive devices are sent to a licensed laboratory for analysis; a continuous monitor produces its own time-series data and average.

Placement is based on the home's structure, not simply the room that is easiest to reach. Illinois calls for a measurement in each lowest structural area suitable for occupancy. A home with a basement, a room over a crawlspace, and a slab-on-grade section may therefore need a measurement for each foundation area.

After the Test

The report shows the measured radon concentration in picocuries per liter (pCi/L). EPA recommends fixing a home at 4.0 pCi/L or higher and considering a fix between 2.0 and 4.0 pCi/L. That action level is a decision point, not a boundary between “safe” and “unsafe.”

The next step also depends on context. Illinois uses a follow-up strategy after an elevated initial homeowner test outside a sale, while a valid real-estate measurement at or above 4.0 pCi/L leads to a recommendation to fix the home. Ask an Illinois-licensed measurement professional about test validity; ask an Illinois-licensed mitigation professional about system design.