For the occupants of a home, actual radon exposure depends on how they use the home, where in the home the occupants spend their time, and how much fresh air is brought into the living area. Since these factors may vary over time, the only reliable way of measuring the actual radon exposure is to conduct a long-term test for at least three months, under normal living conditions.
In the past, prospective homeowners have often been reluctant to purchase a home before performing a long-term test, for fear of not being able to correct a radon problem afterward. However, improved technology and the proven durability of radon mitigation systems have served to reduce much of that concern.
This does not mean that a short-term test is less valuable as part of a home inspection process; but rather, if the results of that test show a potential radon concern, a long-term test can more accurately show actual average radon levels. By conducting a long-term test after moving into a home, the homeowner can control test conditions and, if needed, make decisions on how a mitigation system will be installed.
The placement of the test device within the home must be in accordance with the manufacturer's instructions.