How to Detect Radon in Your Home? | Simple Home Test Rules

Testing a home is the only way to know if radon is present, since the gas is invisible and odorless.

Radon is a radioactive gas that forms when uranium in soil and rock breaks down, and it can seep into homes through foundation cracks. There is no smell, taste, or color to warn you, so the only reliable way to detect it is to run an air-sampling test. This guide covers device placement, running a short-term test correctly, and what results mean.

Where to Place a Radon Test in Your Home

The EPA says to test in the lowest level suitable for occupancy, ideally a room people use regularly. For a single-family home, that usually means the finished basement, or the first floor if the basement is unfinished and rarely entered. In a multi-unit building, the CDC advises testing the lowest level within your own unit rather than a shared basement.

Placement matters just as much as location. Set the device at least 20 inches above the floor, and keep it away from exterior walls, windows, doors, vents, drafts, high heat, and high humidity. Skip kitchens, bathrooms, laundry rooms, and hallways entirely; the humidity and airflow in those spaces skew the sample. Once the test is running, leave it undisturbed.

You can buy a test kit online or by phone from the National Radon Program Services at Kansas State University (1-800-767-7236), or through state radon programs, home improvement stores, and radon measurement professionals. The EPA and CDC both say homeowners can use a DIY kit or hire a professional tester, so the choice comes down to budget and control. The EPA’s own page lets you find a radon test kit and connect with qualified mitigators.

How Do You Run a Short-Term Test the Right Way?

Running a short-term test correctly comes down to following the kit’s instructions exactly and keeping the house closed up beforehand. For any test lasting less than four days, the EPA says to close all windows and exterior doors for at least 12 hours before the test begins. Keep them closed except for normal entry and exit during sampling; open windows let outdoor air dilute radon and produce a false low reading.

Short-term tests run 2 to 90 days depending on the kit, so the exact timing is controlled by the package directions. Each kit is calibrated for a specific exposure window, so the instructions on the package always win. The device must sit undisturbed for the full period. When the time is up, seal it and ship it to the lab listed on the kit, then wait for the analysis.

Common mistakes that ruin results include testing in a bathroom or kitchen, placing the device too close to the floor or too near a draft, forgetting to keep windows closed, and ending the test early. All are avoidable with careful setup and patience.

What a Test Result of 4 pCi/L Means

If your first short-term result comes back at 4 pCi/L or higher, the EPA recommends fixing your home. Before scheduling any work, the EPA recommends a follow-up test to confirm that first reading. If the first short-term result was 8 pCi/L or higher — more than twice the action level — do a second short-term test immediately, then act on the confirmation.

Real-estate transactions commonly use short-term testing because it fits the closing timeline, but the EPA notes that long-term testing, which runs more than 90 days, gives a better estimate of the true annual average. The CDC agrees that exact test length depends on the specific kit.

If a confirmed result stays at 4 pCi/L or above, the usual fix is a mitigation system: a vent fan and pipe that pull radon from beneath the foundation and release it above the roofline. The EPA describes radon testing as easy and inexpensive, though total cost varies by kit type and whether you hire a professional.

Before you buy, our tested picks for the best at-home radon detectors compare the models that gave the most reliable readings in real homes.