Test Mitigation Planner
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:
to (90 days)
to (120 days)
These are the optimum dates. If you begin the test at any other time, you will have to extend it to get the right balance of cold and warm weather, and will have to wait even longer to get your test results.
Try it for yourself with this next calculator. No matter what start date you pick, if you want an unbiased test, the only way to get an earlier end date is to shorten the test period.
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.
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Super quick and efficient service of installing a radon mitigation system in the house we were selling. The installers were very knowledgeable and explained the system and the information to pass on to the buyer's. Definitely would recommend.
(a) at least ten feet off the ground,
(b) above the eave (not necessarily the edge) of the roof, and
(c) either ten feet away from, or two feet above, windows.