Short-term vs long-term radon tests
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How short-term and long-term radon tests differ, which devices are used, and how to combine them before deciding on a fix.
Radon tests fall into two groups based on how long the device stays in place. Each has a job.
Short-term tests (2 to 90 days)
Short-term tests are the usual first step. Common devices include activated charcoal canisters, alpha-track or electret detectors used for short periods, and electronic continuous radon monitors. Charcoal kits typically run 2 to 7 days and are mailed to a lab.
Strengths: fast and inexpensive; good for screening and for real estate deadlines. Limits: radon changes from day to day and season to season, so a short test is a snapshot. It may read higher or lower than your annual average.
Long-term tests (more than 90 days)
Long-term tests typically use alpha-track or electret detectors left in place for 3 months to a year.
Strengths: they average over changing weather and seasons, giving a result closer to your year-round exposure. EPA describes a long-term test as giving a better picture of your average level. Limits: you wait months for an answer.
Continuous radon monitors
Electronic monitors record radon hour by hour. Professional-grade monitors are used by credentialed testers, especially for real estate. Consumer digital monitors can be useful for tracking trends over time; check whether a model is listed or certified for accuracy before relying on it for a decision.
How EPA combines them
EPA’s Citizen’s Guide recommends:
- Take a short-term test.
- If the result is 4 pCi/L or higher, take a follow-up test: long-term for a better average, or a second short-term if you need results quickly.
- Fix the home if the long-term result is 4 pCi/L or higher, or if the average of your first and second short-term tests is 4 pCi/L or higher.
If your first short-term result is below 4 pCi/L, EPA suggests considering a test again in the future, especially if your living patterns change. Our follow-up planner applies these steps.
Seasonal effects to keep in mind
Winter tests with the house closed up often read higher than summer tests. That is one reason a long-term test is valuable when a short-term result is near the decision point, such as 3 to 5 pCi/L.
Quality matters more than type
Whatever you choose, follow the placement and closed-house instructions. EPA notes that test devices meeting recognized standards are reliable when used correctly. Most bad results come from bad placement or open windows, not bad devices. See how to test your home.