How to Test for Radon Yourself: Setup, Placement, Results

A radon test goes wrong more often from sloppy setup than from a bad kit. Put the detector in a drafty spot or crack a window halfway through, and the number you get back is a guess. Radon is a radioactive gas that seeps up from soil into homes, and the EPA identifies it as the leading cause of lung cancer among people who have never smoked. You can't see or smell it, so testing is the only way to know.

What do you need before you start a radon test?

You need a radon test kit, a pen, something to hold the detector off the floor, and about a week of ordinary household routines.

• A radon test kit from a hardware store, home center, or your state radon program. Expect roughly $15 to $70. Confirm the lab analysis fee and prepaid mailer are included, since some kits charge separately.
• A pen for the start and stop times on the form.
• A string, hook, or small table to keep the detector 20 inches or more off the floor.
• A sticky note reading 'Radon test in progress, please don't move.'

Many state radon offices sell discounted kits, and the EPA's indoor air quality pages point to radon resources. Choose a kit that names the lab and its state or national radon proficiency approval. A box with no lab information isn't worth the savings.

Should you buy a short-term or long-term radon test?

Buy a short-term test first, because it gives you an answer in about a week and tells you whether you need to do anything else.

Radon levels shift with weather, soil moisture, and how your house breathes, so a three-day reading is a snapshot and a 90-day reading is closer to what you actually breathe. We'd pick this path for most people: run a short-term test now, and follow with a long-term test only if the result lands close to 4 pCi/L and you aren't in a hurry. A digital monitor suits anyone who wants to watch changes over time, but it's a poor first purchase.

How do you set up closed-house conditions for a radon test?

Closed-house conditions mean keeping windows and exterior doors shut for 12 hours before the test starts and throughout any test shorter than four days.

Normal comings and goings are fine. Walking out for the mail doesn't spoil anything. Propping a door for ventilation, running a window fan, or leaving the garage entry open during a project does.

1. Check the forecast. Avoid starting a short-term test right before a major storm or a stretch of strong wind, which can skew the number.
2. Close all windows, including basement windows, starting 12 hours before you open the kit.
3. Turn off whole-house fans, attic fans, and window fans that move outside air. Your furnace, heat pump, or central air can keep running, and so can window air conditioners that only recirculate indoor air.
4. Use the fireplace or wood stove only if it's your normal heat source, since both draw air out of the house.
5. Tell everyone in the house what's going on, including teenagers and houseguests.

Cold months make a good testing window. Windows are closing anyway, and radon levels in many homes tend to run higher in winter. A summer test with windows shut and the AC on can read lower than what you'd see in January.

Where should you place a radon test kit?

Place the kit in the lowest level of your home that you use regularly, such as a finished basement, family room, or ground-floor bedroom.

If the basement is unfinished and you never spend time there, test the lowest living level instead. If you plan to finish the basement, test there now. Within the room, the details count:

• Set it 20 inches to 6 feet off the floor, roughly breathing height.
• Keep it at least 3 feet from exterior doors and windows, and 12 inches from exterior walls.
• Leave at least 4 inches of open space around it so air can reach it.
• Stay out of kitchens, bathrooms, laundry rooms, closets, and crawl spaces. Humidity and steam throw off charcoal kits.
• Keep it away from supply vents, fans, and direct sun or heat sources.
• Stay clear of the sump pit, floor drains, and any other opening to the soil. Readings right beside them aren't representative of the room.

Once it's placed, don't move it. Dusting around it is fine; relocating it to vacuum is not.

What do you do during the test, and what if someone opens a door?

Leave the detector alone, log anything unusual, and restart with a fresh kit if a door or window stood open for hours.

Open the kit, write the start date and time on the form, hang it in position, and put your note nearby. Keep a quick log of storms, high wind, furnace trouble, or a door left open. Most people run the test three to seven days, and 48 hours is the usual minimum for a short-term kit. Then write down the end date and time and close the kit as the instructions say.

If a guest props a door for a couple of minutes while carrying in groceries, carry on and note it. If a window sat open overnight, a whole-house fan ran for hours, or the heat went out for a day, the result isn't reliable. Don't stretch the test and hope. Buy a fresh kit and restart with a new 12-hour closed-house period. A second kit costs less than acting on a wrong number.

How do you seal, ship, and read your results?

Seal the kit as soon as the test ends, mail it right away, and expect lab results in roughly a week or two.

Follow the kit's instructions for sealing the package, and fill out the form completely: address, location in the house, and start and stop times. Missing times can delay or void a result. The report gives a number in picocuries per liter (pCi/L). Some labs use becquerels per cubic meter instead, and 4 pCi/L is about 148 Bq/m3.

Treat 4 as a decision point, not a line between safe and dangerous. The EPA says no level of radon is risk-free; 4 is where it recommends taking action.

When should you retest or call a radon mitigation contractor?

Retest if your first result is 4 pCi/L or higher, and call a radon mitigation contractor when a second test confirms an average at or above 4.

For the retest, use another short-term test under the same closed-house rules, in the same spot, and average the two numbers. A first result of 8 or higher is reason to start getting quotes while the second test runs.

The standard fix is active soil depressurization. A pipe runs from beneath the slab, or from a membrane over a crawl space, up through the house or an outside wall and out above the roofline, with an inline fan pulling the gas out before it enters the living space. Typical U.S. costs often run about $1,000 to $2,500, with crawl spaces, complex foundations, and long pipe runs pushing the price higher.

Two things people try that don't solve it: caulking foundation cracks alone (the EPA says sealing by itself isn't a reliable fix) and buying an air purifier. Purifiers and whole-house air cleaners handle airborne particles, not radon gas. For general ventilation and air-sealing background, the Department of Energy's Energy Saver pages are a useful starting point.

After mitigation, test again to confirm the system works, and plan to retest every couple of years or after remodeling. Your next step is simple: order a short-term kit today, and set a reminder for the 12 hours before you open it.