Testing · 7 min read
Short-Term vs Long-Term Testing
Short-term radon tests give fast answers; long-term tests give accurate annual averages. Here is when to use each and how to interpret conflicting results.
Radon concentrations fluctuate hour to hour and season to season, sometimes by a factor of several. A test measures a slice of time, and how large that slice is determines what the number represents.
Short-term tests answer whether a problem may exist. Long-term tests answer what a household is actually breathing across a year.
How short-term testing works
A short-term test runs from 2 to 7 days under closed-house conditions. It is fast, inexpensive, and fits any deadline.
The trade-off is representativeness. A test run during a stormy week with saturated soil will read higher than one run during a dry, breezy stretch, and neither reflects the annual average precisely.
How long-term testing works
A long-term test runs 90 days at minimum and ideally a full year, integrating exposure across weather patterns and seasonal behavior.
The result is the number that best predicts health risk, because health risk depends on cumulative exposure rather than on any particular week.
Which to use when
The decision usually resolves itself once the purpose is clear.
- Real estate deadline: short-term, using a continuous monitor.
- General homeowner curiosity with no deadline: long-term, for the most useful answer.
- Elevated short-term result: mitigate, or confirm with a second test first.
- Result between 2.0 and 4.0 pCi/L: long-term follow-up clarifies whether the annual average is a concern.
- Post-mitigation verification: short-term continuous monitor, with an optional long-term confirmation.
When results disagree
It is common for a short-term and long-term test in the same home to differ, sometimes substantially. That is not a sign that one was wrong; they measured different periods.
When they conflict, the long-term result is the better basis for a health decision, and the short-term result is the better basis for understanding worst-case conditions. If either is above the action level, mitigation is reasonable.
Seasonal considerations in San Diego
Locally, winter tends to produce higher readings than summer, because homes are closed more and wet soil pushes gas toward foundations. A summer test near the action level therefore deserves a winter or long-term follow-up.
The mild climate also means many households ventilate heavily during shoulder seasons, which can produce a reassuringly low short-term number that does not reflect closed conditions.
Key takeaways
- Short-term tests are fast; long-term tests are representative.
- Deadlines call for short-term continuous monitor testing.
- Long-term results better predict health risk.
- Disagreement between tests is normal and interpretable.