How to test your home for radon

Testing is the only way to know your radon level. It is also one of the cheapest home safety checks you can do.

Get a test kit

EPA points to several sources:

• Your state radon program. Some states offer free or discounted kits. Find yours on our state pages.
• National Radon Program Services at Kansas State University, which EPA notes sells discounted kits online.
• Hardware and home stores and online retailers. Choose a kit that includes lab analysis, and follow the directions for mailing it back.
• A credentialed radon measurement professional, who can use continuous monitors. EPA says state programs keep lists of professionals credentialed through a state license or a national proficiency program (NRPP or NRSB).

Short-term or long-term?

• Short-term tests stay in place for 2 to 90 days, often 2 to 4 days for common charcoal kits. They are quick and cheap.
• Long-term tests stay in place more than 90 days and better reflect your year-round average.

EPA’s usual path is a short-term test first, then a follow-up if the result is 4 pCi/L or higher. See short-term vs long-term tests and the follow-up planner.

Where to place the test

EPA’s Citizen’s Guide recommends testing in the lowest level of the home that is used, or could be used, as living space, such as a basement you use or plan to finish, or the first floor if there is no basement. Within that level:

• Put the kit in a room used regularly, but not the kitchen, bathroom, or laundry room (humidity and fans can affect results).
• Place it at least 20 inches above the floor, away from drafts, heat sources, and exterior walls, where it will not be disturbed.
• Keep it away from windows and outside doors.

Closed-house conditions for short tests

For tests shorter than four days, EPA’s guidance is to keep windows and outside doors closed (except for normal coming and going) for at least 12 hours before and during the test. Normal heating and air conditioning can run, but avoid fans that bring in outside air. Do not test during severe storms or unusually high winds, which can change indoor pressure.

Common mistakes

• Opening windows during the test.
• Placing the kit in a humid kitchen or bathroom.
• Forgetting to record start and stop dates and times.
• Letting a mailed kit sit too long before it reaches the lab. Mail it promptly after the test ends.
• Moving the device partway through.

Reading the result

The lab reports your average level in pCi/L. Enter it in our radon level calculator to see how it compares with EPA’s action level of 4 pCi/L and the “consider fixing” range of 2 to 4 pCi/L.

When to retest

EPA suggests retesting after a mitigation system is installed, after major renovations or changes to heating and cooling, if you start using a lower level as living space, and every so often even when earlier results were low.

A step-by-step testing checklist

Before the test

• Choose a test: short-term (2 to 90 days) for screening, long-term (90+ days) for a year-round average.
• Check that the kit includes lab analysis, and note any time limit for mailing it back.
• Pick the lowest level of the home that's used regularly, or could be. A finished basement counts, and an unfinished one you rarely enter usually doesn't.
• For short-term tests, start closed-house conditions at least 12 hours before: keep windows and exterior doors closed except for normal entry and exit.

During the test

• Place the device about 20 inches or more above the floor, in a room you use, away from drafts, heat sources, high humidity, and exterior walls.
• Don't place it in kitchens, bathrooms, laundry rooms, or closets.
• Keep heating and cooling running normally. Don't run whole-house fans or window fans that bring in outside air.
• Note the start date and time on the kit or form.
• Avoid testing during severe storms or periods of unusually high winds, if the kit instructions advise it.

After the test

• Record the end date and time.
• Seal the device and mail it to the lab the same day if possible.
• Keep the paperwork, and read the lab report when it arrives.

Understanding your result

• Below 2 pCi/L: low. EPA still suggests testing again sometime in the future, and after changes such as renovations or starting to use a lower level.
• 2 to 4 pCi/L: EPA suggests considering a fix. A long-term test can clarify your year-round average.
• 4 pCi/L or higher: confirm with a follow-up test. If the long-term result, or the average of two short-term tests, is 4 pCi/L or higher, EPA recommends fixing the home.

For context, EPA reports the U.S. average indoor level is about 1.3 pCi/L and the average outdoor level about 0.4 pCi/L.

Digital monitors

Consumer digital radon monitors provide continuous readings and are useful for watching trends, such as higher levels in winter or at night, and for checking that a mitigation system keeps working. For decisions about fixing a home or for real estate, use a lab-analyzed test or a professional measurement. EPA has reviewed testing device performance and says the data support its position that radon testing devices provide accurate and reliable results when used properly.

Hiring a professional tester

You might hire a certified measurement professional when:

• you're buying or selling, and need a documented test on a deadline;
• you want continuous monitoring with hourly data;
• you need testing in a multifamily building or a large home;
• you want an independent check on a mitigation system.

Your state radon office can tell you whether testers must be licensed in your state, and national certification bodies list credentialed professionals.

Common testing mistakes

• Opening windows during a short-term test.
• Placing the kit on the floor, in a closet, or next to a sump pit.
• Mailing the kit days late, which can make results unreliable.
• Testing a level nobody uses while skipping the basement bedroom.
• Testing only once and assuming the number never changes.