How to Test for Radon

Testing is the only way to find out whether your home has a radon problem. Radon is colorless and odorless, so no amount of inspection will reveal it — only measurement will. The good news is that testing is inexpensive and easy to do yourself.

This guide follows U.S. EPA guidance and its action level of 4 pCi/L (148 Bq/m³). Other countries use different reference levels (Canada’s guideline, for example, is 200 Bq/m³), so check your national or local guidance if you live outside the United States.

Choose your test type

There are three main options, and the right one depends on how quickly you need a result and how much detail you want.

For a first test, a short-term kit is a practical starting point. If the result comes back at or above 4 pCi/L (148 Bq/m³), follow up before deciding on mitigation — see Reading your result.

Where to place the test

Put the test in the lowest level of your home that you use regularly — the basement if it is frequently used, otherwise the ground floor. Radon enters from the soil, so levels tend to be higher on lower floors.

Placement guidance from the EPA:

• In a room that is used regularly, such as a living room, playroom, den or bedroom — not a kitchen or bathroom.
• At least 20 inches (50 cm) above the floor, where it won’t be disturbed.
• Away from drafts, high heat, high humidity, and exterior walls.

Your test kit’s instructions may add more specific distances or conditions; follow them.

If you start spending time in a lower level — for example, you finish the basement or turn it into a bedroom — test again on that level. Testing for a home sale follows somewhat different rules; see Radon Test for Home Inspection.

How to run a short-term charcoal test

1. Buy a test kit from a hardware store, home center, or online. Look for kits that carry a state certification or national radon proficiency program listing.
2. Open the kit in the room you have chosen and note the start time. Follow the manufacturer’s instructions — most ask you to hang or place the charcoal canister at the right height.
3. Keep the house closed. For a test lasting only 2 or 3 days, close windows and outside doors at least 12 hours before you start, and keep them closed as much as possible (normal entry and exit is fine) until the test ends.
4. Seal and mail the kit when the exposure time is up, and send it to the lab right away. The EPA says to expect results within a few weeks.

Reading your result

Results are reported in picocuries per liter (pCi/L) in the United States, or becquerels per cubic meter (Bq/m³) in Canada and Europe. To convert: 1 pCi/L = 37 Bq/m³. For more detail, see How to Read Radon Test Results.

The EPA recommends these steps:

1. First short-term test at or above 4 pCi/L (148 Bq/m³): take a follow-up test to be sure. Choose a long-term test for a better picture of your year-round average, or a second short-term test if you need results quickly. If the first result is more than twice the action level — above 8 pCi/L (296 Bq/m³) — take a second short-term test immediately.
2. Decide using the follow-up:
   • Long-term follow-up at or above 4 pCi/L (148 Bq/m³): fix your home.
   • Second short-term test: consider fixing your home if the average of the two tests is 4 pCi/L (148 Bq/m³) or higher. The higher the results, the more certain you can be.

A single short-term test is a snapshot, not a final verdict. Radon levels change with weather, season, and how you use your home.

Using a continuous monitor

A continuous digital monitor measures radon at regular intervals and stores a running history. This is useful if you want to:

• Understand how your levels change with weather and seasons.
• Confirm that a mitigation system keeps working after installation.
• Get an ongoing picture rather than a single snapshot.

What to do if levels are high

If a follow-up test confirms 4 pCi/L (148 Bq/m³) or higher, the EPA recommends hiring a certified mitigation contractor. The most common fix is sub-slab depressurization: a pipe and fan system that draws radon from below the foundation and vents it outside. Most homes can be reduced to 2 pCi/L (74 Bq/m³) or below.

After the system is installed, test again to confirm that the level has come down, and retest from time to time to make sure it stays low. See how often to test for radon.