Question: Are short-term radon tests reliable?

Answer: There is substantial documentation to show that short-term tests, those less than 90 days, generate a large percentage of false positives.

As an example, levels tend to higher in the winter than in the summer. Somewhat high levels may not matter if the test is taken in a basement which is hardly used. etc. Turning on a bathroom or kitchen exhaust fan can change indoor air pressure and thus radon levels.

For information, see the EPA's "Technical Support Document for the 1992 Citizen's Guide to Radon," Exhibit 3-5 as well as "Element of Risk: The Politics of Radon" by Leonard Cole (ISBN #0-19-509367-4).