How to Test Your Home for Radon and Understand the Result
Radon cannot be seen or smelled, so homes must be measured; EPA recommends follow-up after an elevated short-term result and action at 4 pCi/L or higher, while noting that lower levels still carry some risk.
Timeline
- Initial check: Place an approved test in the lowest level that is or could be regularly occupied and follow device conditions exactly.
- After an elevated short-term result: Confirm with a long-term test or a second short-term test under EPA guidance.
- After mitigation: Retest to verify that the installed system reduced the radon level.
Radon is a radioactive gas that enters buildings from soil and cannot be detected by sight or smell. A neighboring house's result does not establish the level in another home, and EPA says its regional radon map should not decide whether an individual home needs testing. The direct way to know is to measure the home's indoor air. [1][2]
A short-term test remains in place from a few days up to 90 days, depending on the device, and provides a quicker screening result. A long-term test remains for more than 90 days and is more likely to represent the year-round average because indoor radon varies with weather, season, ventilation and how the building is used. [1][3]
Placement and conditions affect the result. EPA materials direct users to follow the kit instructions, use the lowest level that is or could be regularly occupied, keep the device away from drafts, heat and high humidity, and maintain specified closed-building conditions for a short test. Opening windows or moving the device can make the measurement less representative. [1][3]
EPA's action level is 4 picocuries per liter of air, also expressed as about 150 becquerels per cubic meter. After an initial short-term result at or above that level, EPA recommends follow-up testing. A long-term test can better estimate the annual average; when results are high or a decision is urgent, a second short-term test can provide faster confirmation. [1][4]
The action level is not a line between harmless and dangerous air. EPA states that some risk remains below 4 pCi/L and advises considering reduction between 2 and 4 pCi/L. Decisions can also reflect smoking, time spent on lower floors and local requirements. Health risk should be discussed with a qualified clinician, while building work belongs with a qualified radon professional. [2][4]
Mitigation commonly uses a system that draws radon-containing soil gas from beneath the building and vents it safely outdoors. The exact design depends on foundation type and local standards. A contractor should explain the system, electrical needs, warning indicator and maintenance. Testing after installation is essential because the goal is a measured reduction, not merely the presence of equipment. [1][3]
Retesting is useful after major renovations, foundation or ventilation changes, a move into a lower level, or the passage of time. In a property sale, buyers may request a recent test performed under documented conditions. The durable process is test, confirm an elevated result, mitigate when indicated and test again, using state radon programs and EPA resources to find current requirements. [3][5]
Sources
- U.S. EPA — A Citizen's Guide to Radon
- U.S. EPA — Map of Radon Zones and Supplemental Information
- U.S. EPA — Home Buyer's and Seller's Guide to Radon
- U.S. EPA — Understanding pCi/L and Radon Action Levels
- U.S. EPA — How Often to Test or Retest for Radon