High Radon Test Result? What the Number Means and What to Do

Radon is measured in picocuries per liter of air (pCi/L).

In metric units the action level of 4 pCi/L is 150 becquerels per cubic meter.

EPA ranks radon as the second leading cause of lung cancer, after smoking.

Radon is a natural radioactive gas that comes from the ground — soil, rock, and groundwater — and can collect inside buildings. EPA estimates about 21,000 radon-related lung cancers a year, and says nearly one in 15 U.S. homes has a level that should be reduced. High levels have been found in every state, so a neighbor’s result says little about yours.

Radon varies from day to day and season to season, so one short test is a starting point.

EPA’s Citizen’s Guide lays out the sequence. Short-term tests stay in the home for two to 90 days; long-term tests stay for more than 90 days and are more likely to reflect the year-round average.

1. If a first short-term test reads 4 pCi/L or higher, take a follow-up test.
2. Follow up with a long-term test for a better picture of the yearly average, or a second short-term test if you need an answer quickly. If the first result was more than twice the action level — above 8 pCi/L — take the second short-term test immediately.
3. Fix the home if a long-term follow-up reads 4 pCi/L or more, or consider fixing it if the average of the two short-term tests is 4 or more.

It is a building system, installed by a trained professional.

EPA recommends hiring a professional trained to mitigate radon, who can study the home and choose the reduction system. EPA describes systems that use special fans and venting to move accumulated radon gas outside the home. EPA says some systems reduce radon levels by up to 99%, and that even very high levels can be brought down to acceptable levels.

Before signing, ask what level the system is designed to reach, how the result will be verified afterward, and where the fan and vent pipe will be placed.

A low result today is not permanent.

EPA advises retesting if you begin to use a lower level of the home, such as a finished basement, and suggests testing again at some point even after a result below 4 pCi/L. If you plan to sell, EPA’s advice is to test now and fix a high level before the house goes on the market.