The best way to determine your annual average radon level is (surprise!) to conduct a year-long test. You can also get a good estimate of this number with a shorter test. The EPA suggests 90 days or more, while some authorities (ourselves included) recommend 120.
Just any old 90 or 120 day period won't do, though. Radon levels tend to increase as the outdoor temperature drops, so you need a test period that has a balance of cold and warm weather. For any specified test duration, there are only two such periods, one in the Spring and the other in the Fall. If you have not yet begun your test, we recommend using these start and end dates:
You can also use this calculator to find the best end date for a test that is already under way.
These calculations are based on weather data for for Ann Arbor, Michigan,
but also work surprisingly well in other climates. For example, they are accurate to within one day for Houston, Texas.
20 years assisting clients with radon, lead paint, mold,
and other environmental air quality issues in their homes
Proudly serving the following Southeast Michigan (SE Mich, MI) counties and communities:
Washtenaw County, Livingston County, Lenawee County, Jackson County, Wayne County, Oakland County, Macomb County, Monroe County, Hillsdale County, Ingham County, Lapeer County, Saint Clair County
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