Radon is a naturally occurring gas that exists in the dirt and air. It is colorless, odorless, and radioactive, and can cause cancer. According to the EPA, homes should be tested for unsafe levels of radon. If you test, keep the windows closed.
Radon tests can be done by homeowners. Radon tests are also performed by professional radon inspectors and mitigators when a home is bought or sold. Since large amounts of radon can enter a home through a crack as small as 1/2 inch, it is important to have all windows closed during the test.
All windows in the home need to be closed for 12 hours prior to the test and left closed during the entire test. A window opened briefly during the test can raise radon levels. If a window is left open for a long period of time, it could dilute radon levels.
In order to have a valid radon test, be sure everyone involved understands the requirement for closed windows. This includes all family members, real estate agents and inspectors. If the homeowner opens the windows during a test, then the test cannot be considered valid. It should be thrown out and another test completed.